EPICS pvDataCPP

Introduction

pvData is one of a set of related projects. It describes and implements the data that the other projects support. Thus it is not useful by itself but understanding pvData is required in order to understand the other projects. The reader should also become familar with projects pvAccess and pvIOC, which are located via the same sourceforge site as this project.

The Java and C++ implementation of pvData implement the same data model but differ in implementation because of the differences between Java and C++.

It is a good idea to read all of pvDataJava.html but read at least the first two chapters:

Introduction

A brief descripton of pvData.

PVData Meta Language

A language used to describe data.

The material in these two chapters is NOT repeated in this documentation.

Doxygen documentation is available at doxygenDoc

Namespace and Memory Management

Namespace

All code in project pvDataCPP appears in namespace:

namespace epics { namespace pvData {
     // ...
}}

Memory Managemment

pvDataCPP introspection and data objects are designed to be shared. They are made availiable via std::tr1::shared_ptr. In addition arrays are implemented via std::vector. The following naming conventions are used in typedefs:

Ptr

When Ptr appears it stands for std::tr1::shared_ptr.

Array

When Array appears it stands for std::vector.

As an example pvType.h includes the following definitions:

typedef std::vector<double> DoubleArray;
typedef std::tr1::shared_ptr<DoubleArray> DoubleArrayPtr;
inline double * get(DoubleArray &value)
{
    return &value[0];
}
inline const double * get(const DoubleArray &value)
{
    return static_cast<const double *>(&value[0]);
}
typedef std::vector<double>::iterator DoubleArray_iterator;
typedef std::vector<double>::const_iterator DoubleArray_const_iterator;

where

DoubleArray

This defines a vector for an array of the primitive type "double".

DoubleArrayPtr

This devices a shared pointer to a vector for an array of the primitive type "double".

get

This gets the raw array of doubles that the DoubleArray holds.

DoubleArray_iterator

This gets a iterator for the DoubleArray.

DoubleArray_const_iterator

This gets a constant iterator for the DoubleArray.

pvDataApp/pv

Overview

Directory pvDataApp/pv has header files that completely describe pvData. The implementation is provided in directory pvDataApp/factory. Test programs appears in testApp/pv.

NOTES:

interface

The documention uses the word interface. This is an analogy for what the Java implementation implements, i. e. package pv provides Java interfaces. C++ does not have interfaces but directory pv defines classes with public members that are similar to the Java interfaces. Most of the implementation is in factory.

Naming Convertions

The naming convertions for variables, methods, and classes follow the Java convertions, i. e. class name begin with an upper case letter, variables and methods begin with a lower case letter.

A PVStructure is a field that contains an array of subfields. Each field has code for accessing the field. The interface for each field is an interface that extends PVField. Each field also has an introspection interface, which an extension of Field. This section describes the complete set of C++ introspection and data interfaces for pvData.

Class FieldCreate creates introspection objects. Class PVDataCreate creates data objects. Class Convert provides a rich set of methods for converting and copying data between fields.

Directory pvDataApp/pv has the following header files:

pvType.h

C++ definitions for primitive types.

pvIntrospect.h

A complete description of the introspection interfaces.

pvData.h

A complete description of the data interfaces.

convert.h

A facility that converts between data fields.

standardField.h

Provides access to introspection interfaces for standard structures like timeStamp, alarm, etc.

standardPVField.h

Cteates data interfaces for standard data structures like timeStamp, alarm, etc.

pvType.h

This provides C/C++ definitions for the pvData primitive types: boolean, byte, short, int, long, ubyte,ushort, uint,u long,float, double, and string. Because pvData is network data, the C++ implementation must implement the proper semantics for the primitive types.

pvType.h provides the proper semantics.

It has the definitions:

typedef uint8_t  boolean;
typedef int8_t   int8;
typedef int16_t  int16;
typedef int32_t  int32;
typedef int64_t  int64;
typedef uint8_t   uint8;
typedef uint16_t  uint16;
typedef uint32_t uint32;
typedef uint64_t uint64;
// float and double are types
typedef std::string String;

/**
 * A boolean array.
 */
typedef std::vector<uint8> BooleanArray;
typedef std::tr1::shared_ptr<BooleanArray> BooleanArrayPtr;
/* get is same is ubyte*/
typedef std::vector<uint8>::iterator BooleanArray_iterator;
typedef std::vector<uint8>::const_iterator BooleanArray_const_iterator;

/**
 * A byte array.
 */
typedef std::vector<int8> ByteArray;
typedef std::tr1::shared_ptr<ByteArray> ByteArrayPtr;
inline int8 * get(ByteArray &value);
inline int8 const * get(ByteArray const &value);
inline int8 * get(ByteArrayPtr &value);
inline int8 const * get(ByteArrayPtr const &value);
inline ByteArray & getVector(ByteArrayPtr &value);
inline ByteArray const & getVector(ByteArrayPtr const &value);
typedef std::vector<int8>::iterator ByteArray_iterator;
typedef std::vector<int8>::const_iterator ByteArray_const_iterator;

/* similar definitions are present for ALL the primitive types */

where

boolean

A c++ bool has the semantics required for boolean. Only the name is different. C++ code can use either bool or boolean.

int8,...,uint64

Integers present a problem because short, int, and long are C++ reserved words but do not have a well defined number of bits. Thus for C++ the definitions above are used in C++ code. The above definitions have worked on all C++ implementations tested at present. If they break in a future implementation they should be changes via "#ifdef" preprocessor statements.

String

pvData requires that a string be an immutable string that is transfered over the network as a UTF8 encoded string. Since std::string implements copy on write semantics, it can be used for support for immutable strings. It can also be serialized/deserialized as a UTF8 encoded string. Because it is not a C++ primitive the first letter is capitalized. This is the same convention the Java implementation uses.

StringBuilder

This is defined here because to is used by the toString methods defined for both introsection and data objects. The definition above acts like the Java StringBuilder class.

Array definitions

typedefs are provided for an array of each of the primitive types. Note that string is treated like a primitive type/

pvIntrospect.h

This subsection describes pvIntrospect.h This file is quite big so rather than showing the entire file, it will be described in parts.

A primary reason for pvData is to support network access to structured data. pvAccess transports top level pvStructures. In addition a pvAccess server holds a set of pvnames, where each pvname if a unique name in the local network.

Given a pvname PV), it is possible to introspect the field without requiring access to data. The reflection and data interfaces are separate because the data may not be available. For example when a pvAccess client connects to a PV, the client library can obtain the reflection information without obtaining any data. Only when a client issues an I/O request will data be available. This separation is especially important for arrays and structures so that a client can discover the type without requiring that a large data array or structure be transported over the network.

Type Description

Types are defined as:

enum Type {
    scalar,
    scalarArray,
    structure,
    structureArray;
};

class TypeFunc {
public:
    const char* name(Type);
    static void toString(StringBuilder buf,const Type type);
};

enum ScalarType {
    pvBoolean,
    pvByte, pvShort, pvInt, pvLong,
    pvUByte, pvUShort, pvUInt, pvULong,
    pvFloat,pvDouble,
    pvString;
};

namespace ScalarTypeFunc {
public:
    bool isInteger(ScalarType type);
    bool isUInteger(ScalarType type);
    bool isNumeric(ScalarType type);
    bool isPrimitive(ScalarType type);
    ScalarType getScalarType(String const &value);
    const char* name(ScalarType);
    void toString(StringBuilder buf,ScalarType scalarType);
};

Type is one of the following:

scalar

A scalar of one of the scalar types.

scalarArray

An array where every element has the same scalar type.

structure

A structure where each field has a name and a type. Within a structure each field name must be unique but the types can be different.

structureArray

An array where each element is a structure. Each element has the same structure introspection interface.

ScalarType is one of the following:

pvBoolean

Has the value false or true.

pvByte

A signed 8 bit integer.

pvShort

A signed 16 bit integer.

pvInt

A signed 32 bit integer.

pvLong

A signed 64 bit integer.

pvUByte

An unsigned 8 bit integer.

pvUShort

An unsigned 16 bit integer.

pvUInt

An unsigned 32 bit integer.

pvULong

An unsigned 64 bit integer.

pvFloat

A IEEE float.

pvDouble

A IEEE double,

pvString

An immutable string.

TypeFunction is a set of convenience methods for Type

name

Returns the name of the type.

toString

Convert the type to a string.

ScalarTypeFunction is a set of convenience methods for ScalarType

isInteger

Is the scalarType an integer type, i.e. one of pvByte,...pvULong.

isUInteger

Is the scalarType an unsigned integer type, i.e. one of pvUByte,...pvULong

isNumeric

Is the scalarType numeric, i.e. pvByte,...,pvDouble.

isPrimitive

Is the scalarType primitive, i.e. not pvString

name

Returns the name of the scalarType.

getScalarType

Given a string of the form String("boolean"),...,String("string") return the scalarType.

toString

Convert the scalar type to a string.

Introspection Description

This section describes the reflection interfaces which provide the following:

Field

A field:

• Has a Type.
• Can be converted to a string.
• Can be shared. A reference count is kept. When it becomes 0 the instance is automatically deleted.

Scalar

A scalar has a scalarType

ScalarArray

The element type is a scalarType

StructureArray

The field holds an array of structures. Each element has the same Structure interspection interface. A pvAccess client can only get/put entire PVStructure elements NOT subfields of array elements.

Structure

Has fields that can be any of the supported types.

FieldCreate

This is an interface that provides methods to create introspection interfaces. A factory is provides to create FieldCreate.

getFieldCreate

Gets a pointer to the single instance of FieldCreate.

class Field;
class Scalar;
class ScalarArray;
class Structure;
class StructureArray;

typedef std::tr1::shared_ptr<const Field> FieldConstPtr;
typedef std::vector<FieldConstPtr> FieldConstPtrArray;
typedef std::tr1::shared_ptr<const Scalar> ScalarConstPtr;
typedef std::tr1::shared_ptr<const ScalarArray> ScalarArrayConstPtr;
typedef std::tr1::shared_ptr<const Structure> StructureConstPtr;
typedef std::tr1::shared_ptr<const StructureArray> StructureArrayConstPtr;


class Field :
    virtual public Serializable,
    public std::tr1::enable_shared_from_this<Field>
{
public:
    POINTER_DEFINITIONS(Field);
    virtual ~Field();
    Type getType() const{return m_type;}
    virtual String getID() const = 0;
    virtual void toString(StringBuilder buf) const{toString(buf,0);}
    virtual void toString(StringBuilder buf,int indentLevel) const;
 ...
};

class Scalar : public Field{
public:
    POINTER_DEFINITIONS(Scalar);
    virtual ~Scalar();
    typedef Scalar& reference;
    typedef const Scalar& const_reference;

    ScalarType getScalarType() const {return scalarType;}
    virtual void toString(StringBuilder buf) const{toString(buf,0);}
    virtual void toString(StringBuilder buf,int indentLevel) const;
    virtual String getID() const;
    virtual void serialize(ByteBuffer *buffer, SerializableControl *control) const;
    virtual void deserialize(ByteBuffer *buffer, DeserializableContol *control);
 ...
};

class ScalarArray : public Field{
public:
    POINTER_DEFINITIONS(ScalarArray);
    typedef ScalarArray& reference;
    typedef const ScalarArray& const_reference;

    ScalarArray(ScalarType scalarType);
    ScalarType  getElementType() const {return elementType;}
    virtual void toString(StringBuilder buf) const{toString(buf,0);}
    virtual void toString(StringBuilder buf,int indentLevel) const;
    virtual String getID() const;
    virtual void serialize(ByteBuffer *buffer, SerializableControl *control) const;
    virtual void deserialize(ByteBuffer *buffer, DeserializableControl *control);
 ...
};

class StructureArray : public Field{
public:
    POINTER_DEFINITIONS(StructureArray);
    typedef StructureArray& reference;
    typedef const StructureArray& const_reference;

    StructureConstPtr  getStructure() const {return pstructure;}
    virtual void toString(StringBuilder buf,int indentLevel=0) const;
    virtual String getID() const;
    virtual void serialize(ByteBuffer *buffer, SerializableControl *control) const;
    virtual void deserialize(ByteBuffer *buffer, DeserializableControl *control);
 ...
};

class Structure : public Field {
public:
    POINTER_DEFINITIONS(Structure);
    typedef Structure& reference;
    typedef const Structure& const_reference;

   std::size_t getNumberFields() const {return numberFields;}
   FieldConstPtr getField(String const & fieldName) const;
   FieldConstPtr getField(std::size_t index) const;
   std::size_t getFieldIndex(String const &fieldName) const;
   FieldConstPtrArray const & getFields() const {return fields;}
   StringArray const & getFieldNames() const;
   void renameField(std::size_t fieldIndex,String const &newName);
   String getFieldName(std::size_t fieldIndex);
   virtual void toString(StringBuilder buf,int indentLevel) const;
   virtual String getID() const;
   virtual void serialize(ByteBuffer *buffer, SerializableControl *control) const;
   virtual void deserialize(ByteBuffer *buffer, DeserializableControl *control);
 ...
};

class FieldCreate  {
public:
    static FieldCreatePtr getFieldCreate();
    ScalarConstPtr  createScalar(ScalarType scalarType) const
    ScalarArrayConstPtr createScalarArray(ScalarType elementType) const;
    StructureArrayConstPtr createStructureArray(StructureConstPtr const & structure) const;
    StructureConstPtr createStructure (
        StringArray const & fieldNames,
        FieldConstPtrArray const & fields) const;
    StructureConstPtr createStructure (
        String const &id,
        StringArray const & fieldNames,
        FieldConstPtrArray const & fields) const;
    StructureConstPtr appendField(
        StructureConstPtr const & structure,
        String const &fieldName, FieldConstPtr const & field) const;
    StructureConstPtr appendFields(
        StructureConstPtr const & structure,
        StringArray const & fieldNames,
        FieldConstPtrArray const & fields) const;
    FieldConstPtr deserialize(ByteBuffer* buffer, DeserializableControl* control) const;
 ...
};

extern FieldCreatePtr getFieldCreate(); 

Constructor

Note that all constructors are protected or private. The only way to create instances is via FieldCreate. The implementation manages all storage via shared pointers.

toString

Many classes provide this (actually two methods). This method is called to get a string that uses the metadata syntax described in a previous section.

Field

getType

Get the field type.

getID

Get an ID for this introspection interface

Scalar

getScalarType

Get that scalar type.

getID

For each scalarType there is one instance of Scalar. The ID for each is the metadata name for the type, i. e. one of "boolean" , ... , "string".

ScalarArray

getElementType

Get the element type.

getID

For each elemnetType there is one instance of ScalarArray. The ID for each is the metadata name for the type, i. e. one of "boolean[]" , ... , "string[]".

StructureArray

getStructure

Get the introspection interface that each element shares,

getID

This returns the ID[] where ID is the value returned by structure->getID().

Structure

getNumberFields

Get the number of immediate subfields.

getField

Given a name or an index get the introspection interface for the field.

getFieldIndex

Given a name get the index, within the array returned by the next method, of the field.

getFields

Get the array of introspection interfaces for the field,

getFieldNames

Get the array of field names for the subfields.

renameField

Rename the field.

getFieldName

Get the field name for the specified index.

FieldCreate

getFieldCreate

Get the single instance of FieldCreate.

createScalar

Create a scalar introspection instance.

createScalarArray

Create a scalar array introspection instance.

createStructure

Create a structure introspection instance. Two methods are provided where the only difference is that one provides an ID and the other does not. The one without will result in ID "structure".

createStructureArray

Create a structure array introspection instance.

appendField

Append a field to a structure.

appendFields

Append fields to a structure.

deserialize

Deserialize from given byte buffer.

standardField.h

The file standardField.h has a class description for creating or sharing Field objects for standard fields. For each type of field a method is provided. Each creates a structure that has a field named "value" and a set of properyt fields, The property field is a comma separated string of property names of the following: alarm, timeStamp, display, control, and valueAlarm. An example is "alarm,timeStamp,valueAlarm". The method with properties creates a structure with fields named value and each of the property names. Each property field is a structure defining the property. The details about each property is given in the section named "Property". For example the call:

    StructureConstPtr example = standardField->scalar(
        pvDouble,
        "value,alarm,timeStamp");

Will result in a Field definition that has the form:

structure example
    double value
    alarm_t alarm
        int severity
        int status
        string message
    timeStamp_t timeStamp
        long secondsPastEpoch
        int  nanoSeconds
        int userTag

In addition there are methods that create each of the property structures, i.e. the methods named: alarm, .... enumeratedAlarm."

standardField.h contains:

class StandardField;
typedef std::tr1::shared_ptr<StandardField> StandardFieldPtr;

class StandardField {
public:
    static StandardFieldPtr getStandardField();
    ~StandardField();
    StructureConstPtr scalar(ScalarType type,String const &properties);
    StructureConstPtr scalarArray(
        ScalarType elementType, String const &properties);
    StructureConstPtr structureArray(
        StructureConstPtr const & structure,String const &properties);
    StructureConstPtr enumerated();
    StructureConstPtr enumerated(String const &properties);
    StructureConstPtr alarm();
    StructureConstPtr timeStamp();
    StructureConstPtr display();
    StructureConstPtr control();
    StructureConstPtr booleanAlarm();
    StructureConstPtr byteAlarm();
    StructureConstPtr ubyteAlarm();
    StructureConstPtr shortAlarm();
    StructureConstPtr ushortAlarm();
    StructureConstPtr intAlarm();
    StructureConstPtr uintAlarm();
    StructureConstPtr longAlarm();
    StructureConstPtr ulongAlarm();
    StructureConstPtr floatAlarm();
    StructureConstPtr doubleAlarm();
    StructureConstPtr enumeratedAlarm();
 ...
};

scalar

Create a scalar with the specified scalar type and name. A structure will be created with the first element being a scalar with the specified scalar type and name value. The other fields in the structure will be the corresponding property structures.

scalarArray

Create a scalarArray with each element having the specified scalar type and name. A structure will be created with the first element being a scalarArray with name value. The other fields in the structure will be the corresponding property structures.

structureArray

Create a structureArray with the specified structure interface and name. A structure will be created with the first element being a structureArray with the specified structure interface and name value. The other fields in the structure will be the corresponding property structures.

structure

Create a structure with the specified name and fields specified by numFields and fields. A structure will be created with the first element being a structure with the name value and fields specified by numFields and fields. The other fields in the structure will be the corresponding property structures.

enumerated

Create a structure with the specified name and fields for an enumerated structure. If properties are specified then a structure will be created with the first element being a structure with the name value and fields for an enumerated structure. The other fields in the structure will be the corresponding property structures.

alarm

timeStamp

display

control

booleanAlarm

byteAlarm

shortAlarm

intAlarm

longAlarm

floatAlarm

doubleAlarm

enumeratedAlarm

The above provide introspection interfaces for standard properties. See the section on Properties for a description of how these are defined.

pvData.h

This subsection describes pvData.h This file is quite big so rather than showing the entire file, it will be described in parts.

typedefs

These are typedefs for Array and Ptr for the various pvData class definitions, i.e. typdefs for "std::vector" and "std::tr1::shared_ptr".

class PVAuxInfo;
class PostHandler;

class PVField;
class PVScalar;

class PVScalarArray;

class PVStructure;
class PVStructureArray;

typedef std::tr1::shared_ptr<PVAuxInfo> PVAuxInfoPtr;

typedef std::tr1::shared_ptr<PostHandler> PostHandlerPtr;

typedef std::tr1::shared_ptr<PVField> PVFieldPtr;
typedef std::vector<PVFieldPtr> PVFieldPtrArray;
typedef std::vector<PVFieldPtr>::iterator PVFieldPtrArray_iterator;
typedef std::vector<PVFieldPtr>::const_iterator PVFieldPtrArray_const__iterator;

typedef std::tr1::shared_ptr<PVScalar> PVScalarPtr;
typedef std::tr1::shared_ptr<PVScalarArray> PVScalarArrayPtr;

typedef std::tr1::shared_ptr<PVStructure> PVStructurePtr;
typedef std::vector<PVStructurePtr> PVStructurePtrArray;
typedef std::vector<PVStructurePtr>::iterator PVStructurePtrArray_iterator;
typedef std::vector<PVStructurePtr>::const_iterator PVStructurePtrArray_const__iterator;

typedef std::tr1::shared_ptr<PostHandler> PostHandlerPtr

PostHandler is a class that must be implemented by any code that calls setPostHandler. It's single virtual method. postPut is called whenever PVField::postPut is called.

class PostHandler 
{
public:
    POINTER_DEFINITIONS(PostHandler);
    virtual ~PostHandler(){}
    virtual void postPut() = 0;
};

PVField

PVField is the base interface for accessing data. A data structure consists of a top level PVStructure. Every field of every structure of every top level structure has a PVField associated with it.

class PVField
: virtual public Serializable,
  public std::tr1::enable_shared_from_this<PVField>
{
public:
   POINTER_DEFINITIONS(PVField);
   virtual ~PVField();
   virtual void message(String message,MessageType messageType);
   String getFieldName() const ;
   virtual void setRequester(RequesterPtr const &prequester);
   std::size_t getFieldOffset() const;
   std::size_t getNextFieldOffset() const;
   std::size_t getNumberFields() const;
   PVAuxInfoPtr & getPVAuxInfo()
   bool isImmutable() const;
   virtual void setImmutable();
   const FieldConstPtr & getField() const ;
   PVStructure * getParent() const 
   void replacePVField(const PVFieldPtr&  newPVField);
   void renameField(String const &newName);
   void postPut() ;
   void setPostHandler(PostHandlerPtr const &postHandler);
   virtual bool equals(PVField &pv);
   virtual void toString(StringBuilder buf) ;
   virtual void toString(StringBuilder buf,int indentLevel);
   std::ostream& dumpValue(std::ostream& o) const;
 ...
}

The public methods for PVField are:

~PVField

Destructor. Since shared pointers are used it should never be called by user code.

message

Code attached to this field can call this method to report problems.

getFieldName

Get the field name. If the field is a top level structure the field name will be an empty string.

setRequester

Sets a requester to be called when message or getRequesterName are called. This is only legal for the top level PVField.

getFieldOffset

Get offset of the PVField field within top level structure. Every field within the PVStructure has a unique offset. The top level structure has an offset of 0. The first field within the structure has offset equal to 1. The other offsets are determined by recursively traversing each structure of the tree.

getNextFieldOffset

Get the next offset. If the field is a scalar or array field then this is just offset + 1. If the field is a structure it is the offset of the next field after this structure. Thus (nextOffset - offset) is always equal to the total number of fields within the field.

getNumberFields

Get the total number of fields in this field. This is nextFieldOffset - fieldOffset.

getPVAuxInfo

Get the PVAuxInfo for this field. PVAuxInfo is described below.

isImmutable

Is the field immutable?

setImmutable

Make the field immutable. Once a field is immutable it can never be changed since there is no method to again make it mutable. This is an important design decision since it allows immutable array fields to share the internal primitive data array.

getField

Get the reflection interface for the data.

getParent

Get the interface for the parent or null if this is the top level PVStructure.

replacePVField

Replace the data implementation for the field.

renameField

Rename the field name.

postPut

If a postHandler is registered it is called otherwise no action is taken.

setPostHandler

Set the postHandler for the record. Only a single handler can be registered.

equals

Compare this field with another field. The result will be true only if the fields have exactly the same field types and if the data values are equal.

toString

Converts the field data to a string. This is mostly for debugging purposes.

dumpValue

Method for streams I/O.

PVAuxInfo

AuxInfo (Auxillary Information) is information about a field that is application specific. It will not be available outside the application that implements the database. In particular it will not be made available to Channel Access. It is used by the database itself to override the default implementation of fields. The JavaIOC uses it for attaching support code. Database Configuration and other tools can use it for configuration information. Each Field and each PVField can have have an arbitrary number of auxInfos. An auxInfo is a (key,PVScalar) pair where key is a string.

class PVAuxInfo : private NoDefaultMethods {
public:
    typedef std::map<String,PVScalarPtr> PVInfoMap;
    typedef std::map<String,PVScalarPtr>::iterator PVInfoIter;
    typedef std::pair<String,PVScalarPtr> PVInfoPair;

    PVAuxInfo(PVField *pvField);
    ~PVAuxInfo();
    PVField * getPVField();
    PVScalarPtr createInfo(String const &key,ScalarType scalarType);
    PVScalarPtr getInfo(String const &key);
    PVInfoMap & getInfoMap();
    void toString(StringBuilder buf);
    void toString(StringBuilder buf,int indentLevel);
 ...
};

where

getPVField

Get the PVField to which this PVAuxInfo is attached.

createInfo

Create a new PVScalar of type scalarType.

getInfo

Get the PVScalar with the specified key.

getInfoMap

Get the map of all the PVScalars that hold the info.

toString

Print all the auxInfos

PVScalar

This is the base class for all scalar data.

class PVScalar : public PVField {
public:
    POINTER_DEFINITIONS(PVScalar);
    virtual ~PVScalar();
    typedef PVScalar &reference;
    typedef const PVScalar& const_reference;
    const ScalarConstPtr getScalar() const ;
 ...
}

where

getScalar

Get the introspection interface for the PVScalar.

PVScalarValue

The interfaces for primitive data types are:

template<typename T>
class PVScalarValue : public PVScalar {
public:
    POINTER_DEFINITIONS(PVScalarValue);
    typedef T value_type;
    typedef T* pointer;
    typedef const T* const_pointer;
    virtual ~PVScalarValue() {}
    virtual T get() const = 0;
    virtual void put(T value) = 0;
 ...
}

// PVString is special case, since it implements SerializableArray
class PVString : public PVScalarValue<String>, SerializableArray {
public:
    virtual ~PVString() {}
 ...
};

where

get

Get the value stored in the object.

put

Change the value stored in the object.

PVArray

PVArray is the base interface for all the other PV Array interfaces. It extends PVField and provides the additional methods:

class PVArray : public PVField, public SerializableArray {
public:
    POINTER_DEFINITIONS(PVArray);
    virtual ~PVArray();
    virtual void setImmutable();
    std::size_t getLength() const;
    virtual void setLength(std::size_t length);
    std::size_t getCapacity() const;
    bool isCapacityMutable() const;
    void setCapacityMutable(bool isMutable);
    virtual void setCapacity(std::size_t capacity) = 0;
 ...
};

setImmutable

Set the data immutable. Note that this is permanent since there is no methods to make it mutable.

getLength

Get the current length. This is less than or equal to the capacity.

setLength

Set the length. If the PVField is not mutable then an exception is thrown. If this is greater than the capacity setCapacity is called.

getCapacity

Get the capacity, i.e. this is the size of the underlying data array.

setCapacity

Set the capacity. The semantics are implementation dependent but typical semantics are as follows: If the capacity is not mutable an exception is thrown. A new data array is created and data is copied from the old array to the new array.

isCapacityMutable

Is the capacity mutable

setCapacityMutable

Specify if the capacity can be changed.

setCapacity

Set the capaciity.

PVArrayData

This is the argument to one of the get methods of PVValueArray.

template<typename T>
class PVArrayData {
private:
    std::vector<T> init;
public:
    POINTER_DEFINITIONS(PVArrayData);
    typedef T  value_type;
    typedef T* pointer;
    typedef const T* const_pointer;
    std::vector<T> & data;
    std::size_t offset;
    PVArrayData()
    : data(init)
    {}
};

PVScalarArray

PVScalarArray is the base class for scalar array data. PVValueArray is a templete for the various scalar array data classes. There is a class for each possible scalar type, i. e. PVBooleanArray, ..., PVStringArray.

class PVScalarArray : public PVArray {
public:
    POINTER_DEFINITIONS(PVScalarArray);
    virtual ~PVScalarArray();
    typedef PVScalarArray &reference;
    typedef const PVScalarArray& const_reference;
    const ScalarArrayConstPtr getScalarArray() const ;
    virtual std::ostream& dumpValue(std::ostream& o, size_t index) const = 0;
 ...
}

where

getScalarArray

Get the introspection interface.

dumpValue

Method for streams I/O.

PVValueArray

This is a template class plus instances for PVBooleanArray, ..., PVStringArray.

template<typename T>
class PVValueArray : public PVScalarArray {
public:
    POINTER_DEFINITIONS(PVValueArray);
    typedef T  value_type;
    typedef T* pointer;
    typedef const T* const_pointer;
    typedef PVArrayData<T> ArrayDataType;
    typedef std::vector<T> vector;
    typedef const std::vector<T> const_vector;
    typedef std::tr1::shared_ptr<vector> shared_vector;
    typedef PVValueArray & reference;
    typedef const PVValueArray & const_reference;

    virtual ~PVValueArray() {}
    virtual std::size_t get(
         std::size_t offset, std::size_t length, ArrayDataType &data) = 0;
    virtual std::size_t put(std::size_t offset,
        std::size_t length, const_pointer from, std::size_t fromOffset) = 0;
    virtual std::size_t put(std::size_t offset,
        std::size_t length, const_vector &from, std::size_t fromOffset);
    virtual void shareData(
         shared_vector const & value,
         std::size_t capacity,
         std::size_t length) = 0;
    virtual pointer get() = 0;
    virtual pointer get() const = 0;
    virtual vector const & getVector() = 0;
    virtual shared_vector const & getSharedVector() = 0;
    std::ostream& dumpValue(std::ostream& o) const;
    std::ostream& dumpValue(std::ostream& o, size_t index) const;
protected:
    PVValueArray(ScalarArrayConstPtr const & scalar)
    : PVScalarArray(scalar) {}
    friend class PVDataCreate;
};

template<typename T>
std::size_t PVValueArray<T>::put(
    std::size_t offset,
    std::size_t length,
    const_vector &from,
    std::size_t fromOffset)
{ return put(offset,length, &from[0], fromOffset); }

/**
 * Definitions for the various scalarArray types.
 */
typedef PVArrayData<uint8> BooleanArrayData;
typedef PVValueArray<uint8> PVBooleanArray;
typedef std::tr1::shared_ptr<PVBooleanArray> PVBooleanArrayPtr;

typedef PVArrayData<int8> ByteArrayData;
typedef PVValueArray<int8> PVByteArray;
typedef std::tr1::shared_ptr<PVByteArray> PVByteArrayPtr;

typedef PVArrayData<int16> ShortArrayData;
typedef PVValueArray<int16> PVShortArray;
typedef std::tr1::shared_ptr<PVShortArray> PVShortArrayPtr;

typedef PVArrayData<int32> IntArrayData;
typedef PVValueArray<int32> PVIntArray;
typedef std::tr1::shared_ptr<PVIntArray> PVIntArrayPtr;

typedef PVArrayData<int64> LongArrayData;
typedef PVValueArray<int64> PVLongArray;
typedef std::tr1::shared_ptr<PVLongArray> PVLongArrayPtr;

typedef PVArrayData<uint8> UByteArrayData;
typedef PVValueArray<uint8> PVUByteArray;
typedef std::tr1::shared_ptr<PVUByteArray> PVUByteArrayPtr;

typedef PVArrayData<uint16> UShortArrayData;
typedef PVValueArray<uint16> PVUShortArray;
typedef std::tr1::shared_ptr<PVUShortArray> PVUShortArrayPtr;

typedef PVArrayData<uint32> UIntArrayData;
typedef PVValueArray<uint32> PVUIntArray;
typedef std::tr1::shared_ptr<PVUIntArray> PVUIntArrayPtr;

typedef PVArrayData<uint64> ULongArrayData;
typedef PVValueArray<uint64> PVULongArray;
typedef std::tr1::shared_ptr<PVULongArray> PVULongArrayPtr;

typedef PVArrayData<float> FloatArrayData;
typedef PVValueArray<float> PVFloatArray;
typedef std::tr1::shared_ptr<PVFloatArray> PVFloatArrayPtr;

typedef PVArrayData<double> DoubleArrayData;
typedef PVValueArray<double> PVDoubleArray;
typedef std::tr1::shared_ptr<PVDoubleArray> PVDoubleArrayPtr;

typedef PVArrayData<String> StringArrayData;
typedef PVValueArray<String> PVStringArray;
typedef std::tr1::shared_ptr<PVStringArray> PVStringArrayPtr;

where

get( std::size_t offset, std::size_t length, ArrayDataType &data)

This method "exposes" it's internal array by setting data.data and data.offset. The caller is responsible for copying the array elements. This violates the principle that objects should not expose their internal data but is done for efficency. For example it makes it possible to copy between arrays with identical element types without requiring an intermediate array.

put(std::size_t offset, std::size_t length, const_pointer from, std::size_t fromOffset)

Put data into the array. from is a raw array.

put(std::size_t offset, std::size_t length, const_vector &from, std::size_t fromOffset)

Put data into the array from a vector holding the raw array.

shareData( shared_vector const & value, std::size_t capacity, std::size_t length)

Make the instance share the raw data from value.
One use is for immutable arrays. In this case the caller must set the PVArray to be immutable. In the PVArray is not immutable then it is the applications responsibility to coordinate access to the array. Again this violates the principle that objects should not expose their internal data but is important for immutable arrays. For example pvData and the javaIOC define many enumerated structures where an enumerated structure has two fields: index and choices. Choices is a PVStringArray that holds the enumerated choices. Index is a PVInt that is the index of the currently selected choice. For many enumerated structures choices is immutable. Allowing the choices internal String[] to be shared between all the instances of an enumerated structure saves on storage.
Another use for shared data is an application which processes an array via multiple modules. Each accesses the internal data array of a PVArray. In this case it is the applications responsibility to coordinate access to the array.

get()

Get the raw array.

getVector()

Get the vector holding the raw array.

getSharedVector()

Get the shared vector holding the data.

dumpValue

Method for streams I/O.

Both get and put return the number of elements actually transfered. The arguments are:

offset

The offset in the PV array.

len

The maximum number of elements to transfer. The number actually transfered will be less than or equal to this value.

data

Get sets data.data to it's internal array and data.offset to the offset into the array. The caller is responsible for the actual data transfer.

from

The array from which the data is taken. This array is supplied by the caller

fromOffset

The offset in from

The caller must be prepared to make multiple calls to retrieve or put an entire array. A caller should accept or put partial arrays. For example the following reads an entire array:

void getArray(PVDoubleArrayPtr & pv,DoubleArray const & to)
{
    size_t len = pv->getLength();
    if(to.size()<len) to.resize(len);
    DoubleArrayData data;
    size_t offset = 0;
    while(offset<len) {
        size_t num = pv->get(offset,(len-offset),data);
        DoubleArray &from = data.data;
        size_t fromOffset = data.offset;
        for(size_t i=0; i<num; i++) to[i+offset] = from[i + fromOffset];
        offset += num;
    }
} 

PVStructure

The interface for a structure is:

class PVStructure : public PVField,public BitSetSerializable {
public:
    POINTER_DEFINITIONS(PVStructure);
    virtual ~PVStructure();
    typedef PVStructure & reference;
    typedef const PVStructure & const_reference;
    virtual void setImmutable();
    StructureConstPtr getStructure() const;
    const PVFieldPtrArray & getPVFields() const;
    PVFieldPtr getSubField(String const &fieldName) const;
    PVFieldPtr getSubField(std::size_t fieldOffset) const;
    void appendPVField(
        String const &fieldName,
        PVFieldPtr const & pvField);
    void appendPVFields(
        StringArray const & fieldNames,
        PVFieldPtrArray const & pvFields);
    void removePVField(String const &fieldName);
    PVBooleanPtr getBooleanField(String const &fieldName) ;
    PVBytePtr getByteField(String const &fieldName) ;
    PVShortPtr getShortField(String const &fieldName) ;
    PVIntPtr getIntField(String const &fieldName) ;
    PVLongPtr getLongField(String const &fieldName) ;
    PVUBytePtr getUByteField(String const &fieldName) ;
    PVUShortPtr getUShortField(String const &fieldName) ;
    PVUIntPtr getUIntField(String const &fieldName) ;
    PVULongPtr getULongField(String const &fieldName) ;
    PVFloatPtr getFloatField(String const &fieldName) ;
    PVDoublePtr getDoubleField(String const &fieldName) ;
    PVStringPtr getStringField(String const &fieldName) ;
    PVStructurePtr getStructureField(String const &fieldName) ;
    PVScalarArrayPtr getScalarArrayField(
        String const &fieldName,ScalarType elementType) ;
    PVStructureArrayPtr getStructureArrayField(String const &fieldName) ;
    String getExtendsStructureName() const;
    bool putExtendsStructureName(
        String const &extendsStructureName);
    virtual void serialize(
        ByteBuffer *pbuffer,SerializableControl *pflusher) const ;
    virtual void deserialize(
        ByteBuffer *pbuffer,DeserializableControl *pflusher);
    virtual void serialize(ByteBuffer *pbuffer,
        SerializableControl *pflusher,BitSet *pbitSet) const;
    virtual void deserialize(ByteBuffer *pbuffer,
        DeserializableControl*pflusher,BitSet *pbitSet);
    PVStructure(StructureConstPtr const & structure);
    PVStructure(StructureConstPtr const & structure,PVFieldPtrArray const & pvFields);
};

where

getStructure

Get the introspection interface for the structure.

getPVFields

Returns the array of subfields. The set of subfields must all have different field names.

getSubField(String fieldName)

Get a subField of a field. For a PVStructure a non-null result is returned if fieldName is a field of the PVStructure. The fieldName can be of the form name.name... If the field does not exist the a Ptr to a NULL value is returned without any error message being generated.

getSubField(int fieldOffset)

Get the field located a fieldOffset, where fieldOffset is relative to the top level structure. This returns null if the specified field is not located within this PVStructure.

appendPVField

Append pvField to the end of this PVStructure. This should NOT be called if any code is attached to any of the fields in the top level structure.

appendPVFields

Append an array of pvFields to the end of this structure. Note that if the original number of fields is 0 than pvFields replaces the original. Thus the caller must NOT reuse pvFields after calling this method. This should NOT be called if any code is attached to any of the fields in the top level structure

removePVField

Remove the specified field from this structure. This should NOT be called if any code is attached to any of the fields in the top level structure.

getBooleanField

Look for fieldName. If found and it has the correct type return the interface. This and the following methods are convenience methods that allow a user to get the interface to a subfield without requiring introspection. fieldName can be of the form name.name... If the field does not exist or has the wrong type then message will be called and a Ptr to NULL is returned.

getByteField

Look for fieldName. If found and it has the correct type return the interface.

getShortField

Look for fieldName. If found and it has the correct type return the interface.

getIntField

Look for fieldName. If found and it has the correct type return the interface.

getLongField

Look for fieldName. If found and it has the correct type return the interface.

getUByteField

Look for fieldName. If found and it has the correct type return the interface.

getUShortField

Look for fieldName. If found and it has the correct type return the interface.

getUIntField

Look for fieldName. If found and it has the correct type return the interface.

getULongField

Look for fieldName. If found and it has the correct type return the interface.

getFloatField

Look for fieldName. If found and it has the correct type return the interface.

getDoubleField

Look for fieldName. If found and it has the correct type return the interface.

getStringField

Look for fieldName. If found and it has the correct type return the interface.

getStructureField

Look for fieldName. If found and it has the correct type return the interface.

getScalarArrayField

Look for fieldName. If found and it has the correct type return the interface.

getStructureArrayField

Look for fieldName. If found and it has the correct type return the interface.

getExtendsStructureName

Get the name of structure that this structure extends.

putExtendsStructureName

Specify the structure that this structure extends.

PVStructureArray

The interface for an array of structures is:

typedef PVArrayData<PVStructurePtr> StructureArrayData;

class PVStructureArray : public PVArray
{
public:
    POINTER_DEFINITIONS(PVStructureArray);
    typedef PVStructurePtr  value_type;
    typedef PVStructurePtr* pointer;
    typedef const PVStructurePtr* const_pointer;
    typedef PVArrayData<PVStructurePtr> ArrayDataType;
    typedef std::vector<PVStructurePtr> vector;
    typedef const std::vector<PVStructurePtr> const_vector;
    typedef std::tr1::shared_ptr<vector> shared_vector;
    typedef PVStructureArray &reference;
    typedef const PVStructureArray& const_reference;

    virtual ~PVStructureArray() {}
    virtual void setCapacity(size_t capacity);
    virtual void setLength(std::size_t length);
    virtual StructureArrayConstPtr getStructureArray() const ;
    virtual std::size_t append(std::size_t number);
    virtual bool remove(std::size_t offset,std::size_t number);
    virtual void compress();
    virtual std::size_t get(std::size_t offset, std::size_t length,
        StructureArrayData &data);
    virtual std::size_t put(std::size_t offset,std::size_t length,
        const_vector const & from, std::size_t fromOffset);
    virtual void shareData(
         shared_vector const & value,
         std::size_t capacity,
         std::size_t length);
    virtual void serialize(ByteBuffer *pbuffer,
        SerializableControl *pflusher) const;
    virtual void deserialize(ByteBuffer *buffer,
        DeserializableControl *pflusher);
    virtual void serialize(ByteBuffer *pbuffer,
        SerializableControl *pflusher, std::size_t offset, std::size_t count) const ;
    virtual pointer get() { return &((*value.get())[0]); }
    virtual pointer get() const { return &((*value.get())[0]); }
    virtual vector const & getVector() {return *value;}
    virtual shared_vector const & getSharedVector() {return value;}
 ...
}

where

getStructureArray

Get the introspection interface shared by each element.

append

Create new elements and append them to the end of the array. It returns the index of the first new element.

remove

Remove the specfied set of elements. It returns (false,true) if the elements (were not, were) removed. It will not removed any elements unless all requested elements exist or are null. Note that this deletes the element and sets the array element to null. It does not change the array capacity.

compress

This moves all null elements and then changes the array capacity. When done there are no null elements.

The other methods are similar to the methods for other array types.

PVDataCreate

PVDataCreate is an interface that provides methods that create PVField interfaces. A factory is provided that creates PVDataCreate.

class PVDataCreate {
public:
    static PVDataCreatePtr getPVDataCreate();
    PVFieldPtr createPVField(FieldConstPtr const & field);
    PVFieldPtr createPVField(PVFieldPtr const & fieldToClone);
    PVScalarPtr createPVScalar(ScalarConstPtr const & scalar);
    PVScalarPtr createPVScalar(ScalarType scalarType);
    PVScalarPtr createPVScalar(PVScalarPtr const & scalarToClone);
    PVScalarArrayPtr createPVScalarArray(ScalarArrayConstPtr const & scalarArray);
    PVScalarArrayPtr createPVScalarArray(ScalarType elementType);
    PVScalarArrayPtr createPVScalarArray(PVScalarArrayPtr const  & scalarArrayToClone);
    PVStructureArrayPtr createPVStructureArray(StructureArrayConstPtr const & structureArray);
    PVStructurePtr createPVStructure(StructureConstPtr const & structure);
    PVStructurePtr createPVStructure(
        StringArray const & fieldNames,PVFieldPtrArray const & pvFields);
   PVStructurePtr createPVStructure(PVStructurePtr const & structToClone);
 ...
};

extern PVDataCreatePtr getPVDataCreate();

where

createPVField

The PVField is created reusing the Field interface. Two methods are provided. Each calls the corresponding createPVScalar, createPVArray, or createPVStructure depending in the type of the last argument.

createPVScalar

Creates an instance of a PVScalar. Three versions are supplied. The first is passed an introspection interface. The second provides the field name and the scalarType. The last provides a field name and a PVScalar to clone. The newly created PVScalar will have the same auxInfos as the original.

createPVScalarArray

Create an instance of a PVArray. Three versions are supplied. The first is passed an introspection interface. The second provides the field name and the elementType. The last provides a field name and a PVArray to clone. The newly created PVArray will have the same auxInfos as the original.

createPVStructureArray

Create a PVStructureArray. It must be passed a structureToClone. This will become the Structure interface for ALL elements of the PVStructureArray. It MUST be used to create any new array elements.

createPVStructure

Create an instance of a PVStructure. Three methods are provided. The first method uses a previously created structure introspection interface. The second uses a PVField array to initialize the sub-fields. The third initializes the subfields by cloning the fields contained in structToClone. The newly created sub-fields will have the same values and auxInfos as the original. If structToClone is null then the new structure is initialized to have 0 sub-fields.

standardPVField.h

A class StandardPVField has methods for creating standard data fields. Like class StandardField it has two forms of the methods which create a field, one without properties and one with properties. Again the properties is some combination of alarm, timeStamp, control, display, and valueAlarm. And just like StandardField there are methods to create the standard properties. The methods are:

class StandardPVField;
typedef std::tr1::shared_ptr<StandardPVField> StandardPVFieldPtr;

class StandardPVField : private NoDefaultMethods {
public:
    static StandardPVFieldPtr getStandardPVField();
    ~StandardPVField();
    PVStructurePtr scalar(ScalarType type,String const &properties);
    PVStructurePtr scalarArray(ScalarType elementType, String const &properties);
    PVStructurePtr structureArray(StructureConstPtr const &structure,String const &properties);
    PVStructurePtr enumerated(StringArray const &choices);
    PVStructurePtr enumerated(StringArray const &choices, String const &properties);
 ...
}


extern StandardPVFieldPtr getStandardPVField();

convert.h

NOTE about copying immutable array fields. If an entire immutable array field is copied to another array that has the same elementType, both offsets are 0, and the length is the length of the source array, then the shareData method of the target array is called and the target array is set immutable. Thus the source and target share the same primitive array.

This section describes the supported conversions between data types.

• All supported types can be converted to a string. If you ask for a 100 megabyte array to be converted to a string expect a lot of output.
• Conversion from a string to a scalar type.
• Conversion from an array of strings to an array of scalar types.
• Copy between the following types of scalar PVs
  • Numeric type to another numeric type
  • Both have the same type.
  • Either is a string
• Copy between PVArrays that satisfy one of the following.
  • Numeric to numeric
  • Both have the same type.
  • Either is a string.
• Conversions between numeric scalar types.
• Conversions between arrays of numeric type.
• Conversion between compatible structures.
• A utility method the returns the full field name of a field

bool operator==(PVField&, PVField&);

static inline bool operator!=(PVField& a, PVField& b)
{return !(a==b);}


bool operator==(const Field&, const Field&);
bool operator==(const Scalar&, const Scalar&);
bool operator==(const ScalarArray&, const ScalarArray&);
bool operator==(const Structure&, const Structure&);
bool operator==(const StructureArray&, const StructureArray&);

static inline bool operator!=(const Field& a, const Field& b)
{return !(a==b);}
static inline bool operator!=(const Scalar& a, const Scalar& b)
{return !(a==b);}
static inline bool operator!=(const ScalarArray& a, const ScalarArray& b)
{return !(a==b);}
static inline bool operator!=(const Structure& a, const Structure& b)
{return !(a==b);}
static inline bool operator!=(const StructureArray& a, const StructureArray& b)
{return !(a==b);}
class Convert;
typedef std::tr1::shared_ptr<Convert> ConvertPtr;

class Convert {
public:
    static ConvertPtr getConvert();
    ~Convert();
    void getFullName(StringBuilder buf,PVFieldPtr const & pvField);
    bool equals(PVFieldPtr const &a,PVFieldPtr const &b);
    bool equals(PVField &a,PVField &b);
    void getString(StringBuilder buf,PVFieldPtr const & pvField,int indentLevel);
    void getString(StringBuilder buf,PVFieldPtr const & pvField);
    void getString(StringBuilder buf,PVField const * pvField,int indentLevel);
    void getString(StringBuilder buf,PVField const * pvField);
    std::size_t fromString(
        PVStructurePtr const &pv,
        StringArray const & from,
        std::size_t fromStartIndex = 0);
    void fromString(PVScalarPtr const & pv, String const & from);
    std::size_t fromString(PVScalarArrayPtr const & pv, String const &from);
    std::size_t fromStringArray(
        PVScalarArrayPtr const & pv,
        std::size_t offset, std::size_t length,
        StringArray const & from,
        std::size_t fromOffset);
    std::size_t toStringArray(PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        StringArray & to,
        std::size_t toOffset);
    bool isCopyCompatible(FieldConstPtr const & from, FieldConstPtr const & to);
    void copy(PVFieldPtr const & from, PVFieldPtr const & to);
    bool isCopyScalarCompatible(
        ScalarConstPtr const & from,
        ScalarConstPtr const & to);
    void copyScalar(PVScalarPtr const & from, PVScalarPtr const & to);
    bool isCopyScalarArrayCompatible(
        ScalarArrayConstPtr const & from,
        ScalarArrayConstPtr const & to);
    std::size_t copyScalarArray(
        PVScalarArrayPtr const & from,
        std::size_t offset,
        PVScalarArrayPtr const & to,
        std::size_t toOffset,
        std::size_t length);
    bool isCopyStructureCompatible(
        StructureConstPtr const & from, StructureConstPtr const & to);
    void copyStructure(PVStructurePtr const & from, PVStructurePtr const & to);
    bool isCopyStructureArrayCompatible(
        StructureArrayConstPtr const & from, StructureArrayConstPtr const & to);
    void copyStructureArray(
        PVStructureArrayPtr const & from, PVStructureArrayPtr const & to);
    int8 toByte(PVScalarPtr const & pv);
    int16 toShort(PVScalarPtr const & pv);
    int32 toInt(PVScalarPtr const & pv);
    int64 toLong(PVScalarPtr const & pv);
    uint8 toUByte(PVScalarPtr const & pv);
    uint16 toUShort(PVScalarPtr const & pv);
    uint32 toUInt(PVScalarPtr const & pv);
    uint64 toULong(PVScalarPtr const & pv);
    float toFloat(PVScalarPtr const & pv);
    double toDouble(PVScalarPtr const & pv);
    String toString(PVScalarPtr const & pv);
    void fromByte(PVScalarPtr const & pv,int8 from);
    void fromShort(PVScalarPtr const & pv,int16 from);
    void fromInt(PVScalarPtr const & pv, int32 from);
    void fromLong(PVScalarPtr const & pv, int64 from);
    void fromUByte(PVScalarPtr const & pv,uint8 from);
    void fromUShort(PVScalarPtr const & pv,uint16 from);
    void fromUInt(PVScalarPtr const & pv, uint32 from);
    void fromULong(PVScalarPtr const & pv, uint64 from);
    void fromFloat(PVScalarPtr const & pv, float from);
    void fromDouble(PVScalarPtr const & pv, double from);
    std::size_t toByteArray(PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        int8* to,
        std::size_t toOffset);
    std::size_t toShortArray(PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        int16* to,
        std::size_t toOffset);
    std::size_t toIntArray(PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        int32* to,
        std::size_t toOffset);
    std::size_t toLongArray(PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        int64* to,
        std::size_t toOffset);
    std::size_t toUByteArray(PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        uint8* to,
        std::size_t toOffset);
    std::size_t toUShortArray(PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        uint16* to,
        std::size_t toOffset);
    std::size_t toUIntArray(
        PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        uint32* to,
        std::size_t toOffset);
    std::size_t toULongArray(
        PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        uint64* to,
        std::size_t toOffset);
    std::size_t toFloatArray(
        PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        float* to,
        std::size_t toOffset);
    std::size_t toDoubleArray(
        PVScalarArrayPtr const & pv,
        std::size_t offset,
        std::size_t length,
        double* to, std::size_t
        toOffset);
    std::size_t fromByteArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const int8* from, std::size_t fromOffset);
    std::size_t fromByteArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const ByteArray & from, std::size_t fromOffset);
    std::size_t fromShortArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const int16* from, std::size_t fromOffset);
    std::size_t fromShortArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const ShortArray & from, std::size_t fromOffset);
    std::size_t fromIntArray(
       PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
       const int32* from, std::size_t fromOffset);
    std::size_t fromIntArray(
       PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
       const IntArray & from, std::size_t fromOffset);
    std::size_t fromLongArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const int64* from, std::size_t fromOffset);
    std::size_t fromLongArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const LongArray & from, std::size_t fromOffset);
    std::size_t fromUByteArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const uint8* from, std::size_t fromOffset);
    std::size_t fromUByteArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const UByteArray & from, std::size_t fromOffset);
    std::size_t fromUShortArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const uint16* from, std::size_t fromOffset);
    std::size_t fromUShortArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const UShortArray & from, std::size_t fromOffset);
    std::size_t fromUIntArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const uint32* from, std::size_t fromOffset);
    std::size_t fromUIntArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const UIntArray & from, std::size_t fromOffset);
    std::size_t fromULongArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const uint64* from, std::size_t fromOffset);
    std::size_t fromULongArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const ULongArray & from, std::size_t fromOffset);
    std::size_t fromFloatArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const float* from, std::size_t fromOffset);
    std::size_t fromFloatArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const FloatArray & from, std::size_t fromOffset);
    std::size_t fromDoubleArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const double* from, std::size_t fromOffset);
    std::size_t fromDoubleArray(
        PVScalarArrayPtr & pv, std::size_t offset, std::size_t length,
        const DoubleArray & from, std::size_t fromOffset);
    void newLine(StringBuilder buf, int indentLevel);
 ...
}

extern ConvertPtr getConvert();

The array methods all return the number of elements copied or converted. This can be less than len if the PVField array contains less than len elements.

newLine is a convenience method for code that implements toString It generates a newline and inserts blanks at the beginning of the newline.

pvDataApp/property

Definition of Property

Only fields named "value" have properties. A record can have multiple value fields, which can appear in the top level structure of a record or in a substructure. All other fields in the structure containing a value field are considered properties of the value field. The fieldname is also the property name. The value field can have any type, i.e. scalar, scalarArray, or structure. Typical property fields are timeStamp, alarm, display, control, and history. The timeStamp is a special case. If it appears anywhere in the structure hieraracy above a value field it is a property of the value field.

For example the following top level structure has a single value field. The value field has properties alarm, timeStamp, and display.

structure counterOutput
    double value
    alarm_t
        int severity 0
        int status 0
        string message
    timeStamp_t
        long secondsPastEpoch
        int nanoSeconds
        int userTag
    display_t
        double limitLow 0.0
        double limitHigh 10.0
        string description "Sample Description"
        string format "%f"
        string units volts

The following example has three value fields each with properties alarm and timeStamp. Voltage, Current, and Power each have a different alarms but all share the timeStamp.

structure powerSupplyValue
    double value
    alarm_t
        int severity 0
        int status 0
        string message

structure powerSupplySimple
    alarm_t
        int severity 0
        int status 0
        string message
    timeStamp_t
        long secondsPastEpoch
        int nanoSeconds
        int userTag
    powerSupplyValue_t voltage
        double value
        alarm_t
            int severity 0
            int status 0
            string message
    powerSupplyValue_t power
        double value
        alarm_t
            int severity 0
            int status 0
            string message
    powerSupplyValue_t current
        double value
        alarm_t
            int severity 0
            int status 0
            string message

Standard Properties

The following field names have special meaning, i.e. support properties for general purpose clients.

value

This is normally defined since most general purpose clients access this field. All other fields in the structure support or describe the value field. The type can any supported type but is usually one of the following:

scalar

Any of the scalar types.

scalarArray

An array with the elementType being a scalar type

enumerated structure

A structure that includes fields named index and choices. index is an int that selects a choice. choices is an array of strings that defines the complete set of choices.

other

Other structure or array types can also be defined if clients and support code agree on the meaning. Some examples are: 1) A structure defining a 2D matrix, 2) A structure defining an image, 3) A structure that simulates a remote method, ...

timeStamp

The timeStamp. The type MUST be a timeStamp structure. Also if the PVData structure does not have a timeStamp then a search up the parent tree is made to find a timeStamp.

alarm

The alarm. The type MUST be an alarm structure.

display

A display structure as described below. It provides display characteristics for the value field.

control

A control structure as described below. It provides control characteristics for the value field.

history

Provides a history buffer for the value field. Note that currently PVData does not define history suppoprt.

other

Other standard properties can be defined.

In addition a structure can have additional fields that support the value field but are not recognized by most general purpose client tools. Typical examples are:

input

A field with support that changes the value field. This can be anything. It can be a channel access link. It can obtain a value from hardware. Etc.

valueAlarm

A field with support that looks for alarm conditions based on the value.

output

A field with support that reads the current value and sends it somewhere else. This can be anything. It can be a channel access link. It can write a value to hardware. Etc.

The model allows for device records. A device record has structure fields that that support the PVData data model. For example a powerSupport record can have fields power, voltage, current that each support the PVData data model.

Overview of Property Support

Except for enumerated, each property has two files: a property.h and a pvProperty.h . For example: timeStamp.h and pvTimeStamp.h In each case the property.h file defined methods for manipulating the property data and the pvProperty.h provides methods to transfer the property data to/from a pvData structure.

All methods copy data via copy by value semantics, i.e. not by pointer or by reference. No property class calls new or delete and all allow the compiler to generate default methods. All allow a class instance to be generated on the stack. For example the following is permitted:

void example(PVFieldPtr const &pvField) {
    Alarm alarm;
    PVAlarm pvAlarm;
    bool result;
    result = pvAlarm.attach(pvField);
    assert(result);
    Alarm al;
    al.setMessage(String("testMessage"));
    al.setSeverity(majorAlarm);
    result = pvAlarm.set(al);
    assert(result);
    alarm = pvAlarm.get();
     ...
}

timeStamp

A timeStamp is represented by the following structure

structure timeStamp
    long secondsPartEpoch
    int nanoSeconds
    int userTag

The Epoch is the posix epoch, i.e. Jan 1, 1970 00:00:00 UTC. Both the seconds and nanoSeconds are signed integers and thus can be negative. Since the seconds is kept as a 64 bit integer, it allows for a time much greater than the present age of the universe. Since the nanoSeconds portion is kept as a 32 bit integer it is subject to overflow if a value that corresponds to a value that is greater than a little more than 2 seconds of less that about -2 seconds. The support code always adjust seconds so that the nanoSecconds part is normlized, i. e. it has is 0<=nanoSeconds<nanoSecPerSec..

Two header files are provided for manipulating time stamps:

timeStamp.h

Defines a time stamp independent of pvData, i.e. it is a generally useful class for manipulating timeStamps.

pvTimeStamp.h

A class that can be attached to a time stamp pvData structure. It provides get and set methods to get/set a TimeStamp as defined by timeStamp.h

timeStamp.h

This provides

extern int32 milliSecPerSec;
extern int32 microSecPerSec;
extern int32 nanoSecPerSec;
extern int64 posixEpochAtEpicsEpoch;

class TimeStamp {
public:
    TimeStamp()
    :secondsPastEpoch(0), nanoSeconds(0), userTag(0) {}
    TimeStamp(int64 secondsPastEpoch,int32 nanoSeconds = 0,int32 userTag = 0);
    //default constructors and destructor are OK
    //This class should not be extended
    void normalize();
    void fromTime_t(const time_t &);
    void toTime_t(time_t &) const;
    int64 getSecondsPastEpoch() const {return secondsPastEpoch;}
    int64 getEpicsSecondsPastEpoch() const {
        return secondsPastEpoch - posixEpochAtEpicsEpoch;
    }
    int32 getNanoSeconds() const  {return nanoSeconds;}
    int32 getUserTag() const {return userTag;}
    void setUserTag(int userTag) {this->userTag = userTag;}
    void put(int64 secondsPastEpoch,int32 nanoSeconds = 0) {
        this->secondsPastEpoch = secondsPastEpoch;
        this->nanoSeconds = nanoSeconds;
        normalize();
    }
    void put(int64 milliseconds);
    void getCurrent();
    double toSeconds() const ;
    bool operator==(TimeStamp const &) const;
    bool operator!=(TimeStamp const &) const;
    bool operator<=(TimeStamp const &) const;
    bool operator< (TimeStamp const &) const;
    bool operator>=(TimeStamp const &) const;
    bool operator> (TimeStamp const &) const;
    static double diff(TimeStamp const & a,TimeStamp const & b);
    TimeStamp & operator+=(int64 seconds);
    TimeStamp & operator-=(int64 seconds);
    TimeStamp & operator+=(double seconds);
    TimeStamp & operator-=(double seconds);
    int64 getMilliseconds(); // milliseconds since epoch
 ...
}

where

TimeStamp()

The defauly constuctor. Both seconds and nanoSeconds are set to 0.

TimeStamp(int64 secondsPastEpoch,int32 nanoSeconds = 0)

A constructor that gives initial values to seconds and nanoseconds.

normalize

Adjust seconds and nanoSeconds so that 0<=nanoSeconds<nanoSecPerSec.

fromTime_t

Set time from standard C time.

toTime_t

Convert timeStamp to standard C time.

getSecondsPastEpoch

Get the number of seconds since the epoch.

getEpicsSecondsPastEpoch

Get the number of EPICS seconds since the epoch. EPICS uses Jan 1, 1990 00:00:00 UTC as the epoch.

getNanoSeconds

Get the number of nanoSeconds. This is always normalized.

getUserTag

Get the userTag.

setUserTag

Set the userTag.

put(int64 secondsPastEpoch,int32 nanoSeconds = 0)

Set the timeStamp value. If necessary it will be normalized.

put(int64 milliseconds)

Set the timeStamp with a value the is the number of milliSeconds since the epoch.

getCurrent()

Set the timeStamp to the current time.

toSeconds()

Convert the timeStamp to a value that is the number of seconds since the epocj

operator =

operator!=

operator<=

operator<

operator>=

operator>

Standard C++ operators.

diff

diff = a - b

getMilliseconds

Get the number of milliseconds since the epoch.

The TimeStamp class provides arithmetic operations on time stamps. The result is always kept in normalized form, which means that the nano second portion is 0≤=nano<nanoSecPerSec. Note that it is OK to have timeStamps for times previous to the epoch.

TimeStamp acts like a primitive. It can be allocated on the stack and the compiler is free to generate default methods, i.e. copy constructor, assignment constructor, and destructor.

One use for TimeStamp is to time how long a section of code takes to execute. This is done as follows:

    TimeStamp startTime;
    TimeStamp endTime;
    ...
    startTime.getCurrent();
    // code to be measured for elapsed time
    endTime.getCurrent();
    double time = TimeStamp::diff(endTime,startTime);

pvTimeStamp.h

class PVTimeStamp {
public:
    PVTimeStamp();
    //default constructors and destructor are OK
    //This class should not be extended
    //returns (false,true) if pvField(isNot, is valid timeStamp structure
    bool attach(PVFieldPtr const &pvField);
    void detach();
    bool isAttached();
    // following throw logic_error if not attached to PVField
    // a set returns false if field is immutable
    void get(TimeStamp &) const;
    bool set(TimeStamp const & timeStamp);
};

where

PVTimeStamp

The default constructor. Attach must be called before get or set can be called.

attach

Attempts to attach to pvField It returns (false,true) if a timeStamp structure is found. It looks first at pvField itself and if is not an appropriate pvData structure but the field name is value it looks up the parent structure tree.

detach

Detach from the pvData structure.

isAttached

Is there an attachment to a timeStamp structure?

get

Copies data from the pvData structure to a TimeStamp. An exception is thrown if not attached to a pvData structure.

set

Copies data from TimeStamp to the pvData structure. An exception is thrown if not attached to a pvData structure.

alarm

An alarm structure is defined as follows:

structure alarm
    int severity
    int status
    string message

Note that neither severity or status is defined as an enumerated structure. The reason is performance, i. e. prevent passing the array of choice strings everywhere. The file alarm.h provides the choice strings. Thus all code that needs to know about alarms share the exact same choice strings.

Two header files are provided for manipulating alarms:

alarm.h

Defines an alarm independent of pvData, i.e. it is a generally useful class for manipulating alarms.

pvAlarm.h

A class that can be attached to an alarm pvData structure. It provides get and set methods to get/set alarm data as defined by alarm.h

alarm.h

enum AlarmSeverity {
 noAlarm,minorAlarm,majorAlarm,invalidAlarm,undefinedAlarm
};

enum AlarmStatus {
    noStatus,deviceStatus,driverStatus,recordStatus,
    dbStatus,confStatus,undefinedStatus,clientStatus
};


class AlarmSeverityFunc {
public:
    static AlarmSeverity getSeverity(int value);
    static StringArrayPtr getSeverityNames();
};

class AlarmStatusFunc {
public:
    static AlarmStatus getStatus(int value);
    static StringArrayPtr getStatusNames();
};

class Alarm {
public:
    Alarm();
    //default constructors and destructor are OK
    String getMessage();
    void setMessage(String const &value);
    AlarmSeverity getSeverity() const;
    void setSeverity(AlarmSeverity value);
    AlarmStatus getStatus() const;
    void setStatus(AlarmStatus value);
};

Alarm Severity defines the possible alarm severities:

getSeverity

Get the alarm severity corresponding to the integer value.

getSeverityNames

Get the array of severity choices.

Alarm Status defines the possible choices for alarm status:

getStatus

Get the alarm status corresponding to the integer value.

getStatusNames

Get the array of status choices.

Alarm has the methods:

Alarm

The constructor. It sets the severity to no alarm and the message to "".

getMessage

Get the message.

setMessage

Set the message.

getSeverity

Get the severity.

setSeverity

Set the severity.

getStatus

Get the status.

setStatus

Set the status.

pvAlarm.h

class PVAlarm {
public:
    PVAlarm() : pvSeverity(0),pvMessage(0) {}
    //default constructors and destructor are OK
    //returns (false,true) if pvField(isNot, is valid enumerated structure
    //An automatic detach is issued if already attached.
    bool attach(PVFieldPtr const &pvField);
    void detach();
    bool isAttached();
    // each of the following throws logic_error is not attached to PVField
    // set returns false if field is immutable
    void get(Alarm & alarm) const;
    bool set(Alarm const & alarm); 
};

where

PVAlarm

The default constructor. Attach must be called before get or set can be called.

attach

Attempts to attach to pvField It returns (false,true) if it found an appropriate pvData structure. It looks first a pvField itself and if is not an appropriate pvData structure but the field name is value it looks to see if the parent structure has an appropriate sub structure.

detach

Just detaches from the pvData structure.

isAttached

Is there an attachment to an alarm structure?

get

Copies data from the pvData structure to an Alarm. An exception is thrown if not attached to a pvData structure.

set

Copies data from Alarm to the pvData structure. An exception is thrown if not attached to a pvData structure.

control

Control information is represented by the following structure

structure control
    double limitLow
    double limitHigh
    double minStep

Two header files are provided for manipulating control:

control.h

Defines control independent of pvData, i.e. it is a generally useful class for manipulating control.

pvControl.h

A class that can be attached to an control pvData structure. It provides get and set methods to get/set control data as defined by control.h

control.h

class Control {
public:
    Control();
    //default constructors and destructor are OK
    double getLow() const;
    double getHigh() const;
    double getMinStep() const;
    void setLow(double value);
    void setHigh(double value);
    void setMinStep(double value);
};

where

Control

The default constructure.

getLow

Get the low limit.

getHigh

Get the high limit.

setLow

Set the low limit.

setHigh

Set the high limit.

setMinStep

Set the minimum step size.

getMinStep

Get he minimum step size.

pvControl.h

class PVControl {
public:
    PVControl();
    //default constructors and destructor are OK
    //returns (false,true) if pvField(isNot, is valid enumerated structure
    //An automatic detach is issued if already attached.
    bool attach(PVFieldPtr const &pvField);
    void detach();
    bool isAttached();
    // each of the following throws logic_error is not attached to PVField
    // set returns false if field is immutable
    void get(Control &) const;
    bool set(Control const & control);
};

where

PVControl

The default constructor. Attach must be called before get or set can be called.

attach

Attempts to attach to pvField It returns (false,true) if it found an appropriate pvData structure. It looks first a pvField itself and if is not an appropriate pvData structure but the field name is value it looks to see if the parent structure has an appropriate sub structure.

detach

Just detaches from the pvData structure.

isAttached

Is there an attachment to a control structure?

get

Copies data from the pvData structure to a Control. An exception is thrown if not attached to a pvData structure.

set

Copies data from Control to the pvData structure. An exception is thrown if not attached to a pvData structure.

display

Display information is represented by the following structure

structure display
    double limitLow
    double limitHigh
    string description
    string format
    string units

Two header files are provided for manipulating display:

display.h

Defines display independent of pvData, i.e. it is a generally useful class for manipulating display.

pvDisplay.h

A class that can be attached to an display pvData structure. It provides get and set methods to get/set display data as defined by display.h

display.h

class Display {
public:
    Display();
    //default constructors and destructor are OK
    double getLow() const;
    double getHigh() const;
    void setLow(double value);
    void setHigh(double value);
    String getDescription() const;
    void setDescription(String const &value);
    String getFormat() const;
    void setFormat(String const &value);
    String getUnits() const;
    void setUnits(String const &value);
};

where

Control

The default constructure.

getLow

Get the low limit.

getHigh

Get the high limit.

setLow

Set the low limit.

setHigh

Set the high limit.

getDescription

Get the description.

setDescription

Set the description.

getFormat

Get the format.

setFormat

Set the format.

getUnits

Get the units.

setUnits

Set the units.

pvDisplay.h

class PVDisplay {
public:
    PVDisplay()
    : pvDescription(0),pvFormat(),pvUnits(),pvLow(),pvHigh() {}
    //default constructors and destructor are OK
    //An automatic detach is issued if already attached.
    bool attach(PVFieldPtr const&pvField); 
    void detach();
    bool isAttached();
    // each of the following throws logic_error is not attached to PVField
    // a set returns false if field is immutable
    void get(Display &) const;
    bool set(Display const & display);
};

where

PVDisplay

The default constructor. Attach must be called before get or set can be called.

attach

Attempts to attach to pvField It returns (false,true) if it found an appropriate pvData structure. It looks first a pvField itself and if is not an appropriate pvData structure but the field name is value it looks to see if the parent structure has an appropriate sub structure.

detach

Just detaches from the pvData structure.

isAttached

Is there an attachment to a display structure?

get

Copies data from the pvData structure to a Display. An exception is thrown if not attached to a pvData structure.

set

Copies data from Display to the pvData structure. An exception is thrown if not attached to a pvData structure.

pvEnumerated.h

An enumerated structure is a structure that has fields:

structure
    int index
    string[] choices

For enumerated structures a single header file pvEnumerted.h is available

class PVEnumerated {
public:
    PVEnumerated();
    //default constructors and destructor are OK
    //This class should not be extended
    //returns (false,true) if pvField(isNot, is valid enumerated structure
    //An automatic detach is issued if already attached.
    bool attach(PVFieldPtr const &pvField);
    void detach();
    bool isAttached();
    // each of the following throws logic_error is not attached to PVField
    // a set returns false if field is immutable
    bool setIndex(int32 index);
    int32 getIndex();
    String getChoice();
    bool choicesMutable();
    StringArrayPtr const & getChoices();
    int32 getNumberChoices();
    bool setChoices(StringArray &choices,int32 numberChoices);
};

where

PVEnumerated

The default constructor. Attach must be called before any get or set method can be called.

attach

Attempts to attach to pvField It returns (false,true) if pvField (is not, is) an enumerated structure.

detach

Just detaches from the pvData structure.

isAttached

Is there an attachment to an enemerated structure?

setIndex

Set the index field in the pvData structure. An exception is thrown if not attached to a pvData structure.

getIndex

Get the index field in the pvData structure.

getChoice

Get the String value corresponding to the current index field in the pvData structure. An exception is thrown if not attached to a pvData structure.

choicesMutable

Can the choices be changed? Note that this is often true. An exception is thrown if not attached to a pvData structure.

getChoices

Get the array of choices. An exception is thrown if not attached to a pvData structure.

getNumberChoices

Get the number of choices. An exception is thrown if not attached to a pvData structure.

setChoices

Change the choices. An exception is thrown if not attached to a pvData structure.

Examples

Accessing PVData

Assume that code wants to print two fields from a PVStructure:

value

Must be a PVDouble.

timeStamp

Just look for field with this name.

The following code uses introspection to get the desired information.

void getValueAndTimeStamp(PVStructurePtr pvStructure,StringBuilder buf) {
   PVFieldPtr valuePV = pvStructure->getSubField(String("value"));
   if(valuePV.get()==NULL) {
       buf += "value field not found";
       return;
   }
   buf += "value ";
   valuePV->toString(&buf);
   PVFieldPtr timeStampPV = pvStructure->getSubField(String("timeStamp"));
   if(timeStampPV.get()==NULL) {
       buf += "timeStamp field not found";
       return;
   }
   buf += " timeStamp ";
   timeStampPV->toString(&buf);
}

Creating PVData

Example of creating a scalar field.

    PVDataCreatePtr pvDataCreate = getPVDataCreate();
    PVDoublePtr pvValue = static_pointer_cast<PVDouble>(
        pvDataCreate->createPVScalar(pvDouble));

Create a structure with a value and an alarm the hard way

    FieldCreatePtr fieldCreate = getFieldCreate();
    PVDataCreatePtr pvDataCreate = getPVDataCreate();
    FieldConstPtrArray fields;
    StringArray names;
    fields.resize(3);
    names.resize(3);
    fields[0] = fieldCreate->createScalar(pvInt);
    fields[1] = fieldCreate->createScalar(pvInt);
    fields[2] = fieldCreate->createScalar(pvString);
    names[0] = "severity";
    names[0] = "status";
    names[0] = "message";
    StructureConstPtr alarmField =  
        fieldCreate->createStructure(names,fields);
    fields.resize(2);
    names.resize(2);
    fields[0] = fieldCreate->createScalar(pvDouble);
    fields[1] = alarmField;
    names[0] = "value";
    names[0] = "alarm";
    StructureConstPtr structure =
        fieldCreate->createStructure(names,fields);
    PVStructurePtr pv = pvDataCreate->createPVStructure(structure);

Create an alarm structure the easy way.

    StandardPVFieldPtr standardPVField = getStandardPVField();
    PVStructurePtr pv = standardPVField->scalar(pvDouble,"alarm");

Create a PVStructure with field name example that has a double value field , timeStamp, alarm, and display. Do it the easy way.

    StandardPVFieldPtr standardPVField = getStandardPVField();
    PVStructurePtr pvStructure = standardPVField->scalar(
        pvDouble,"timeStamp,alarm.display");

pvDataApp/factory

Directory factory has code that implements everything described by the files in directory pv

TypeFunc.cpp implements the functions for the enums defined in pvIntrospecct.h

FieldCreateFactory.cpp automatically creates a single instance of FieldCreate and implements getFieldCreate.

PVDataCreateFactory.cpp automatically creates a single instance of PVDataCreate and implements getPVDataCreate.

PVAuxInfoImpl.cpp implements auxInfo.

Convert.cpp automatically creates a single instance of Convert and implements getConvert.

Other files implement PVData base classes

pvDataAPP/misc

Overview

This package provides utility code:

bitSet.h

An implementation of BitSet that can be serialized.

byteBuffer.h

Used to serialize objects.

destroyable.h

Provides method destroy.

epicsException.h

Exception with stack trace.

event.h

Signal and wait for an event.

executor.h

Provides a thread for executing commands.

lock.h

Support for locking and unlocking.

messageQueue.h

Support for queuing messages to give to requesters.

noDefaultMethods.h

When privately extended prevents compiler from implementing default methods.

queue.h

A queue implementation that allows the latest queue element to continue to be used when no free element is available.

requester.h

Allows messages to be sent to a requester.

serialize.h

Support for serializing objects.

serializeHelper.h

More support for serializing objects.

sharedPtr.h

Defines POINTER_DEFINITIONS.

status.h

A way to pass status information to a client.

thread.h

Provides thread support.

timeFunction.h

Time how long a function call requires.

timer.h

An implementation of Timer that does not require an object to be created for each timer request.

Note that directory testApp/misc has test code for all the classes in misc. The test code also can be used as examples.

bitSet.h

This is adapted from the java.util.BitSet. bitSet.h is:

class BitSet : public Serializable {
public:
    static BitSet::shared_pointer create(uint32 nbits);
    BitSet();
    BitSet(uint32 nbits);
    virtual ~BitSet();
    void flip(uint32 bitIndex);
    void set(uint32 bitIndex);
    void clear(uint32 bitIndex);
    void set(uint32 bitIndex, bool value);
    bool get(uint32 bitIndex) const;
    void clear();
    int32 nextSetBit(uint32 fromIndex) const;
    int32 nextClearBit(uint32 fromIndex) const;
    bool isEmpty() const;
    uint32 cardinality() const;
    uint32 size() const;
    BitSet& operator&=(const BitSet& set);
    BitSet& operator|=(const BitSet& set);
    BitSet& operator^=(const BitSet& set);
    BitSet& operator-=(const BitSet& set);
    BitSet& operator=(const BitSet &set);
    void or_and(const BitSet& set1, const BitSet& set2);
    bool operator==(const BitSet &set) const;
    bool operator!=(const BitSet &set) const;
    void toString(StringBuilder buffer);
    void toString(StringBuilder buffer, int indentLevel) const;
private:
};

where

BitSet()

Creates a bitSet of initial size 64 bits. All bits initially false.

BitSet(uint32 nbits)

Creates a bitSet with the initial of the specified number of bits. All bits initially false.

~BitSet()

Destructor.

flip(uint32 bitIndex)

Flip the specified bit.

set(uint32 bitIndex)

Set the specified bit true.

clear(uint32 bitIndex)

Set the specified bit false.

set(uint32 bitIndex, bool value)

Set the specified bit to value.

get(uint32 bitIndex)

Return the state of the specified bit.

clear()

Set all bits to false.

nextSetBit(uint32 fromIndex)

Get the index of the next true bit beginning with the specified bit.

nextClearBit(uint32 fromIndex)

Get the index of the next false bit beginning with the specified bit.

isEmpty()

Return (false,true) if (at least one bit true, all bits are false)

cardinality()

Return the number of true bits.

size()

Returns the number of bits of space actually in use.

operator&=(const BitSet& set)

Performs a logical and of this target bit set with the argument bit set. This bit set is modified so that each bit in it has the value true if and only if it both initially had the value true and the corresponding bit in the bit set argument also had the value.

operator|=(const BitSet& set)

Performs a logical or of this target bit set with the argument bit set.

operator^=(const BitSet& set)

Performs a logical exclusive or of this target bit set with the argument bit set.

operator-=(const BitSet& set)

Clears all of the bits in this bitSet whose corresponding bit is set in the specified bitSet.

operator=(const BitSet &set)

Assignment operator.

or_and(const BitSet& set1, const BitSet& set2)

Perform AND operation on set1 and set2, and then OR this bitSet with the result.

operator==(const BitSet &set)

Does this bitSet have the same values as the argument.

operator!=(const BitSet &set)

Is this bitSet different than the argument.

toString(StringBuilder buffer)

Show the current values of the bitSet.

toString(StringBuilder buffer, int indentLevel)

Show the current values of the bitSet.

virtual void serialize(ByteBuffer *buffer,SerializableControl *flusher) const;

Serialize the bitSet

virtual void deserialize(ByteBuffer *buffer,DeserializableControl *flusher);

Deserialize the bitSet.

byteBuffer.h

A ByteBuffer is used to serialize and deserialize primitive data. File byteBuffer.h is:

class ByteBuffer {
public:
    ByteBuffer(std::size_t size, int byteOrder = EPICS_BYTE_ORDER)
    ~ByteBuffer();
    void setEndianess(int byteOrder);
    const char* getBuffer();
    void clear();
    void flip();
    void rewind();
    std::size_t getPosition();
    void setPosition(std::size_t pos);
    std::size_t getLimit();
    void setLimit(std::size_t limit);
    std::size_t getRemaining();
    std::size_t getSize();
    template<typename T>
    void put(T value)
    template<typename T>
    void put(std::size_t index, T value);
    template<typename T>
    T get()
    template<typename T>
    T get(std::size_t index)
    void put(const char* src, std::size_t src_offset, std::size_t count);
    void get(char* dest, std::size_t dest_offset, std::size_t count);
    template<typename T>
    inline void putArray(T* values, std::size_t count)
    template<typename T>
    inline void getArray(T* values, std::size_t count)
    template<typename T>
    inline bool reverse();
    inline void align(std::size_t size)
    void putBoolean(  bool value);
    void putByte   (  int8 value);
    void putShort  ( int16 value);
    void putInt    ( int32 value);
    void putLong   ( int64 value);
    void putFloat  ( float value);
    void putDouble (double value);
    void putBoolean(std::size_t  index,  bool value);
    void putByte   (std::size_t  index,  int8 value);
    void putShort  (std::size_t  index, int16 value);
    void putInt    (std::size_t  index, int32 value);
    void putFloat  (std::size_t  index, float value);
    void putDouble (std::size_t  index, double value);
    bool getBoolean();
    int8 getByte   ();
    int16 getShort  ();
    int32 getInt    ();
    int64 getLong   ();
    float getFloat  ();
    double getDouble ();
    bool getBoolean(std::size_t  index);
    int8 getByte   (std::size_t  index);
    int16 getShort  (std::size_t  index);
    int32 getInt    (std::size_t  index);
    int64 getLong   (std::size_t  index);
    float getFloat  (std::size_t  index);
    double getDouble (std::size_t  index);
    const char* getArray();
 ...
};

destroyable.h

class Destroyable  {
public:
    POINTER_DEFINITIONS(Destroyable);
    virtual void destroy() = 0;
    virtual ~Destroyable() {};
};

epicsException.h

/*
 * Throwing exceptions w/ file+line# and, when possibly, a stack trace
 *
 * THROW_EXCEPTION1( std::bad_alloc );
 *
 * THROW_EXCEPTION2( std::logic_error, "my message" );
 *
 * THROW_EXCEPTION( mySpecialException("my message", 42, "hello", ...) );
 *
 * Catching exceptions
 *
 * catch(std::logic_error& e) {
 *   fprintf(stderr, "%s happened\n", e.what());
 *   PRINT_EXCEPTION2(e, stderr);
 *   cout<<SHOW_EXCEPTION(e);
 * }
 *
 * If the exception was not thrown with the above THROW_EXCEPTION*
 * the nothing will be printed.
 */

event.h

This class provides coordinates activity between threads. One thread can wait for the event and the other signals the event.

class Event;
typedef std::tr1::shared_ptr<Event> EventPtr;
 
class Event {
public:
    POINTER_DEFINITIONS(Event);
    explicit Event(bool = false);
    ~Event();
    void signal();
    bool wait (); /* blocks until full */
    bool wait ( double timeOut ); /* false if empty at time out */
    bool tryWait (); /* false if empty */
private:
    epicsEventId id;
}; 

where

Event

The constructor. The initial value can be full or empty. The normal first state is empty.

signal

The event becomes full. The current or next wait will complete.

wait

Wait until event is full or until timeout. The return value is (false,true) if the wait completed because event (was not, was) full. A false value normally means that that a timeout occured. It is also returned if an error occurs or because the event is being deleted.

tryWait

returns (false,true) if the event is (empty,full)

executor.h

An Executor is a thread that can execute commands. The user can request that a single command be executed.

class Command;
class Executor;
typedef std::tr1::shared_ptr<Command> CommandPtr;
typedef std::tr1::shared_ptr<Executor> ExecutorPtr;
    
class Command {
public:
    POINTER_DEFINITIONS(Command);
    virtual ~Command(){}
    virtual void command() = 0;
private: 
    CommandPtr next;
    friend class Executor;
}; 
 
class Executor :  public Runnable{
public: 
    POINTER_DEFINITIONS(Executor);
    Executor(String threadName,ThreadPriority priority);
    ~Executor();
    void execute(CommandPtr const &node);
    virtual void run();
 ...
};

Command is a class that must be implemented by the code that calls execute. It contains the single virtual method command, which is the command to execute.

Executor has the methods:

Executor

The constructor. A thread name and priority must be specified.

~Executor

The destructor. If any commands remain in the execute list they are not called. All ExecutorNodes that have been created are deleted.

execute

Request that command be executed. If it is already on the run list nothing is done.

lock.h

typedef epicsMutex Mutex;

class Lock : private NoDefaultMethods {
public:
    explicit Lock(Mutex &pm);
    ~Lock();
    void lock();
    void unlock();
    bool tryLock();
    bool ownsLock() ;
 ...
};

Lock is as easy to use as Java synchronize. To protect some object just create a Mutex for the object and then in any method to be synchronized just have code like:

class SomeClass {
private
    Mutex mutex;
 ...
public
    SomeClass() : mutex(Mutex()) {}
 ...
    void method()
    {
        Lock xx(mutex);
        ...
    }

The method will take the lock when xx is created and release the lock when the current code block completes.

Another example of Lock is initialization code that must initialize only once. This can be implemented as follows:

    static void init(void) {
        static Mutex mutex;
        Lock xx(mutex);
        if(alreadyInitialized) return;
        // initialization
    }

messageQueue.h

Definitions

A messageQueue is for use by code that wants to handle messages without blocking higher priority threads.

class MessageNode;
class MessageQueue;
typedef std::tr1::shared_ptr<MessageNode> MessageNodePtr;
typedef std::vector<MessageNodePtr> MessageNodePtrArray;
typedef std::tr1::shared_ptr<MessageQueue> MessageQueuePtr;

class MessageNode {
public:
    String getMessage() const;
    MessageType getMessageType() const;
    void setMessageNull();
};

class MessageQueue : public Queue<MessageNode> {
public:
    POINTER_DEFINITIONS(MessageQueue);
    static MessageQueuePtr create(int size);
    MessageQueue(MessageNodePtrArray &nodeArray);
    virtual ~MessageQueue();
    MessageNodePtr &get();
    // must call release before next get
    void release();
    // return (false,true) if message (was not, was) put into queue
    bool put(String message,MessageType messageType,bool replaceLast);
    bool isEmpty() ;
    bool isFull() ;
    int getClearOverrun();
 ...
};

A messageNode is a class with two public data members:

getMessage

The message.

getMessageType

The message type.

setMessageNull

Set the message to be a null string.

A messageQueue is an interface with public methods:

MessageQueue

The constructor. The queue size must be specified.

~MessageQueue

The destructor.

put

Put a new message into the queue. False is returned if the queue was full and true otherwise. If replaceLast is true then the last message is replaced with this message.

get

Get the oldest queue element. If the queue is empty null is returned. Before the next get can be issued release must be called.

release

Release the queue element returned by the last get.

isEmpty

Is the queue empty?

isFull

Is the queue full?

getClearOverrun

Get the number of times put has been called but no free element is available.

Look at miscTest/testMessageQueue.cpp for an example.

noDefaultMethods.h

If a class privately extends this class then the compiler can not create any of the following: default constructor, default copy constructror, or default assignment contructor.

/* This is based on Item 6 of
 * Effective C++, Third Edition, Scott Meyers
 */
    class NoDefaultMethods {
    protected:
    // allow by derived objects
    NoDefaultMethods(){};
    ~NoDefaultMethods(){}
    private:
    // do not implment
    NoDefaultMethods(const NoDefaultMethods&);
    NoDefaultMethods & operator=(const NoDefaultMethods &);
    };

queue.h

This provides a queue which has an immutable capacity. When the queue is full the user code is expected to keep using the current element until a new free element becomes avalable.

template <typename T>
class Queue
{   
public:
    POINTER_DEFINITIONS(Queue);
    typedef std::tr1::shared_ptr<T> queueElementPtr;
    typedef std::vector<queueElementPtr> queueElementPtrArray;
    Queue(queueElementPtrArray &);
    virtual ~Queue();
    void clear();
    int capacity();
    int getNumberFree();
    int getNumberUsed();
    queueElementPtr & getFree();
    void setUsed(queueElementPtr const &element);
    queueElementPtr & getUsed();
    void releaseUsed(queueElementPtr const &element);
 ...
};

testApp/misc/testQueue.cpp provides an example of how to define a queue.

The queue methods are:

clear

Make the queue empty.

getNumberFree

Get the number of free elements in the queue.

capacity

Get the capacity, i.e. the maximun number of elements the queue can hold.

getNumberFree

Get the number of free elements.

getNumberUsed

Get the number of elements used.

getFree

Get the next free element. Null is returned if no free elements are available. If a non null value is returned then the element belongs to the caller until setUsed is called.

setUsed

Set a queue element used. This must be the element returned by the last call to getFree.

getUsed

Get the next used element of null if no more used elements are available.

releaseUsed

Set a queue element free. This must be the element returned by the last call to getUsed.

A queue is created as follows:

   class MyClass;
   typedef MyQueueElement<MyClass> MyElement;
   typedef MyQueue<MyClass> MyQueue;
   int numElement = 5;
   ...
   MyClass *array[numElements];
   for(int i=0; i<numElements; i++) {
        array[i] = new MyClass();
   }
   MyQueue *queue = new MyQueue(array,numElements);

A producer calls getFree and setUsed via code like the following:

   MyClass *getFree() {
       MyElement *element = queue->getFree();
       if(element==0) return 0;
       return element->getObject();
  }

A consumer calls getUsed and releaseUsed via code like the following:

     while(true) {
         MyElement *element = queue->getUsed();
         if(element==0) break;
         MyClass *myClass = element->getObject();
         // do something with myClass
         queue->releaseUsed(element);
     }

requester.h

A PVField extends Requester. Requester is present so that when database errors are found there is someplace to send a message.

enum MessageType {
   infoMessage,warningMessage,errorMessage,fatalErrorMessage
};

extern String getMessageTypeName(MessageType messageType);
extern const size_t messageTypeCount;
class Requester {
public:
    POINTER_DEFINITIONS(Requester);
    virtual ~Requester(){}
    virtual String getRequesterName() = 0;
    virtual void message(String const & message,MessageType messageType) = 0;
};

where

MessageType

Type of message.

messageTypeName

An array of strings of the message type names, i.e. String("info"),String("warning"),String("error"),String("fatalError").

getRequesterName

Returns the requester name.

message

Gives a message to the requester.

serialize.h

    class SerializableControl;
    class DeserializableControl;
    class Serializable;
    class BitSetSerializable;
    class SerializableArray;
    class BitSet;
    class Field;

    class SerializableControl {
    public:
        virtual ~SerializableControl(){}
        virtual void flushSerializeBuffer() =0;
        virtual void ensureBuffer(std::size_t size) =0;
        virtual void alignBuffer(std::size_t alignment) =0;
        virtual void cachedSerialize(
            std::tr1::shared_ptr<const Field> const & field,
            ByteBuffer* buffer) = 0;
    };

    class DeserializableControl {
    public:
        virtual ~DeserializableControl(){}
        virtual void ensureData(std::size_t size) =0;
        virtual void alignData(std::size_t alignment) =0;
        virtual std::tr1::shared_ptr<const Field> cachedDeserialize(ByteBuffer* buffer) = 0;
    };

    class Serializable {
    public:
        virtual ~Serializable(){}
        virtual void serialize(ByteBuffer *buffer,
            SerializableControl *flusher) const = 0;
        virtual void deserialize(ByteBuffer *buffer,
            DeserializableControl *flusher) = 0;
    };

    class BitSetSerializable {
    public:
        virtual ~BitSetSerializable(){}
        virtual void serialize(ByteBuffer *buffer,
            SerializableControl *flusher,BitSet *bitSet) const = 0;
        virtual void deserialize(ByteBuffer *buffer,
            DeserializableControl *flusher,BitSet *bitSet) = 0;
    };


    class SerializableArray : virtual public Serializable {
    public:
        virtual ~SerializableArray(){}
        virtual void serialize(ByteBuffer *buffer,
            SerializableControl *flusher, std::size_t offset, std::size_t count) const = 0;
    };

serializeHelper.h

This is a helper class for serialization, which is required for sending and receiving pvData over the nerwork.

class SerializeHelper : public NoDefaultMethods {
public:
    static void writeSize(int s, ByteBuffer* buffer,
        SerializableControl* flusher);
    static int readSize(ByteBuffer* buffer,
        DeserializableControl* control);
    static void serializeString(const String& value,
        ByteBuffer* buffer,SerializableControl* flusher);
    static void serializeSubstring(const String& value, int offset,
        int count, ByteBuffer* buffer,
        SerializableControl* flusher);
    static String deserializeString(ByteBuffer* buffer,
        DeserializableControl* control);
 ...
};

where

writeSize

Serialize the size.

readSize

Deserialize the size.

serializeString

Serialize a String.

serializeSubstring

Serialize a substring.

deserializeString

Deserialize a string.

sharedPtr.h

#define POINTER_DEFINITIONS(clazz) \
    typedef std::tr1::shared_ptr<clazz> shared_pointer; \
    typedef std::tr1::shared_ptr<const clazz> const_shared_pointer; \
    typedef std::tr1::weak_ptr<clazz> weak_pointer; \
    typedef std::tr1::weak_ptr<const clazz> const_weak_pointer;

status.h

Status provides a way to pass status back to client code:

class Status : public epics::pvData::Serializable {
    public:
   enum StatusType { 
         /** Operation completed successfully. */
         STATUSTYPE_OK,
         /** Operation completed successfully, but there is a warning message. */
         STATUSTYPE_WARNING,
         /** Operation failed due to an error. */
         STATUSTYPE_ERROR,
         /** Operation failed due to an unexpected error. */
         STATUSTYPE_FATAL
    }; 
    static const char* StatusTypeName[];
    static Status OK;
    Status();
    Status(StatusType type, epics::pvData::String const & message);
    Status(StatusType type, epics::pvData::String const & message, epics::pvData::String stackDump);
    ~Status()
    StatusType getType() const;
    String getMessage() const;
    String getStackDump() const;
    bool isOK() const;
    bool isSuccess() const;
    String toString() const;
    void toString(StringBuilder buffer, int indentLevel = 0) const;
    void serialize(ByteBuffer *buffer, SerializableControl *flusher) const;
    void serialize(ByteBuffer *buffer, SerializableControl *flusher) const;
};

The Status methods are:

StatusType

An enum for the status type.

getType

Get the statusType.

getMessage

Get a message explaining the error.

getStackDump

Get a stack dump.

The StatusCreate methods are:

getStatusOK

Get a singleton that returns StatusType.OK and a null message and stackDump.

createStatus

Create a new Status.

deserializeStatus

Use this method instead of Status.deserialize(), since this allows OK status optimization.

thread.h

ThreadPriority

enum ThreadPriority {
    lowestPriority,
    lowerPriority,
    lowPriority,
    middlePriority,
    highPriority,
    higherPriority,
    highestPriority
};

Thread

class Runnable {
public:
    virtual void run() = 0;
};

class Thread;

class Thread : public epicsThread, private NoDefaultMethods {
public:
    Thread(
        String name,
        ThreadPriority priority,
        Runnable *runnableReady,
        epicsThreadStackSizeClass stkcls=epicsThreadStackSmall);
    ~Thread();
 ...
};

Runnable must be implement by code that wants to be run via a thread. It has one virtual method: run. Run is the code that is run as a thread. When run compeletes it can not be restarted. If code wants to delete a thread then it MUST arrange that the run returns before the thread can be deleted. An exception is thrown if run remains active when delete is called.

Thread has the methods:

Thread

The constructor. A thread name and priority must be specified. The run methods of runnable is executed. When the run methods returns the thread will no longer be active but the client code must still delete the thread.

~Thread

The destructor. This is called as the result of:

    delete pthread;

timeFunction.h

TimeFunction is a facility that measures the average number of seconds a function call requires. When timeCall is called, it calls function in a loop. It starts with a loop of one iteration. If the total elapsed time is less then .1 seconds it increases the number of iterrations by a factor of 10. It keeps repeating until the elapsed time is greater than .1 seconds. It returns the average number of seconds per call.

class TimeFunctionRequester;
class TimeFunction;
typedef std::tr1::shared_ptr<TimeFunctionRequester> TimeFunctionRequesterPtr;
typedef std::tr1::shared_ptr<TimeFunction> TimeFunctionPtr;
        
class TimeFunctionRequester {
public:              
    POINTER_DEFINITIONS(TimeFunctionRequester);
    virtual ~TimeFunctionRequester(){}
    virtual void function() = 0;
};  

    
class TimeFunction {
public:    
    POINTER_DEFINITIONS(TimeFunction);
    TimeFunction(TimeFunctionRequesterPtr const & requester);
    ~TimeFunction(); 
    double timeCall();
 ...
};      

TimeFunctionRequester must be implemented by code that wants to time how long a function takes. It has the single method:

function

This is the function.

TimeFunction has the methods:

TimeFunction

Constructor.

~TimeFunction

Destructor.

timeCall

Time how long it takes to execute the function. It starts by calling the function one time. If it takes < 1 seconds to doubles the number of times to call the function. It repeats this until it takes at least one second to call it ntimes.

timer.h

This provides a general purpose timer. It allows a user callback to be called after a delay or periodically.

class TimerCallback;
class Timer;
typedef std::tr1::shared_ptr<TimerCallback> TimerCallbackPtr;
typedef std::tr1::shared_ptr<Timer> TimerPtr;


class TimerCallback {
public:
    POINTER_DEFINITIONS(TimerCallback);
    TimerCallback();
    virtual ~TimerCallback(){}
    virtual void callback() = 0;
    virtual void timerStopped() = 0;
};

class Timer : private Runnable {
public:
    POINTER_DEFINITIONS(Timer);
    Timer(String threadName, ThreadPriority priority);
    virtual ~Timer();
    virtual void run();
    void scheduleAfterDelay(
        TimerCallbackPtr const &timerCallback,
        double delay);
    void schedulePeriodic(
        TimerCallbackPtr const &timerCallback,
        double delay,
        double period));
    void cancel(TimerCallbackPtr const &timerCallback);
    bool isScheduled(TimerCallbackPtr const &timerCallback);
    void toString(StringBuilder builder);
 ...
};

TimerCallback must be implemented by the user. It has the following methods:

callback

This is called when a timer expires. This is called with no locks held. When called a delay timer is no longer on the queue but a periodioc timer is on a queue. Thus the callback for a delay timer can issue a new schedule request but a periodic timer must not. Note the explaination of TimerNode.cancel below.

timerStopped

Timer.stop was called when a timer request was queued. or if the timer is stopped and a schedule request is made.

In order to schedule a callback client code must allocate a TimerNode It can be used to schedule multiple callbacks. It has the methods:

TimerNode

The constructor. User code must create a TimeNode in order to call a schedule method.

~TimerNode

The destructor. This is called as a result of the client calling:

    delete timerNode;

cancel

This is called to cancel a timer request. If a callback has been dequeued but the callback not called when cancel is called then a callback may still happen. New schedule requests can be made after a cancel request has been made.

isScheduled

Is the timerNode scheduled to be called.

Timer has the methods:

Timer

The consttructor.

~Timer

The destructor. The queue is emptied and TimerCallback.timerStopped is called for each element of the queue.

scheduleAfterDelay

A request to schedule a callback after a delay specified in seconds.

schedulePeriodic

Schedule a periodic callback.

pvDataApp/pvMisc

bitSetUtil.h

The following is also provided:

class BitSetUtil : private NoDefaultMethods {
public:
    static bool compress(BitSet const &bitSet,PVStructure const &pvStructure);
};

This provides functions that operate on a BitSet for a PVStructure. It currently has only one method:

compress

Compress the bits in a BitSet related to a structure.
For each structure:

1. If the bit for the structure is set then the bit for all subfields of the structure are cleared.
2. If the bit for the structure is not set but all immediate subfields have their bit set then the bit for the structure is set and the bits for all subfields are cleared.

Note that this is a recursive algorithm. That is if every immediate subfield has it's offset bit set then the bits for ALL fields that reside in the structure will be cleared.

Channel Access can call this before sending data. It can then pass entire structures if the structure offset bit is set.