V4 Design: dbdClass

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Revision as of 20:07, 24 May 2005 by MartyKraimer (talk | contribs)

== EPICS: dbdClasses - IOC records data == May 24 2005

Overview

This document describes the C++ class definitions for code that implements the semantics for records created from Database Definitions. The definitions are intended for code that:

  • includes header files generated from dbd definitions. Header files are generated from the following dbd definitions:
    • record - Should only be included by record support.
    • struct - Included by code that understands the struct.
    • menu - Included by code that understands the menu.
  • does not include the header files.

The following headers files are described:

  • dbfTypes.h - Type definitions for field definitions in struct or record> DBD definitions.
  • dbdStatements.h - Type definitions for DBD statements.
  • dbdInterfaces.h - Type definitions for interfaces related to DBD definitions.

dbfTypes

File dbfTypes.h describes types and classes that are used in header files generated from dbd struct or record field definitions. The following naming conventions are used:

Dbf
any class starting with Dbf describes a non epicsType struct or record field as it appears in a generated header file. For example DbfString describes a field generated from field(name,string).
Dbd
A class name starting with Dbd describes something directly related to a dbd statement. For example DbdLinkSupport describes a dbd link definition.

dbdTypes.h

enum dbfType {
    dbfUnknownT,
    dbfEpicsT,  // an epicsType except epicsUnknownT
    dbfArrayT,
    dbfStructT,
    dbfMenuT,
    dbfEnumT,
    dbfLinkT,
    dbfDeviceT
};

class DbdStruct; //describes a dbd struct definition
class DbdMenu; //describes a dbd menu definition
class DbdLink;    //describes dbd link statement
class DbdDevice;  //describes dbd device statement

// If array type is a known epicsType then EpicsArray
class DbfArray : public EpicsArray {
public:
    dbfType dbftype;
};

// If every field is a known epicsType then EpicsStruct
class DbfStruct {
public:
    DbdStruct *pDbdStruct;
    void         *pstorage;
};

class DbfMenu{
public:
    epicsInt16    index;
    DbdMenu  *pmenuDef; /* address of global menu */
};

class DbfEnum{
public:
    epicsInt16  index;
    EpicsArray  *pchoiceArray; // addr of field that is array of string
};

enum LinkDir {
    LinkDirNone,
    LinkDirForward,
    LinkDirIn,
    LinkDirOut,
    LinkDirInOut
};

class DbfLink{ 
public:
    LinkDir   dir;
    DbdLink   *plinkDef;
    EpicsStruct dataStruct;
};

class DbfDevice{
public:
    LinkDir   dir;
    DbdDevice *pDbdDevice;
    EpicsStruct dataStruct;
};

Discussion of dbfTypes

The classes defined in dbfTypes together with the definitions from epicsTypes is a complete list of the definitions that appear in header files generated from struct and record dbd definitions.

Epics Types

DBD types bool,...,string all become an epicsType.

DBD type array becomes an EpicsArray if the array type maps to an epicsType or to DbfArray if the type is not an epicsType.

DBD type struct maps to EpicsStruct if all fields in the struct map to an epicsType other than epicsUnknownT or otherwise to DbfStruct.

If a record is defined as: 

    struct(displayLimits) {
        field(low,double)
        field(high,double)
    }
    record(xxx) extends iocRecord {
        ...
        field(fbool,bool)
        field(foctet,octet)
        ...
        field(ffloat64,float64)
        ...
        field(fstring,string)
        field(darray,array(double[])
        field(displayLimits,struct(displayLimits))
    }

Then the generated header file will be 

    class xxxRecord : public iocRecord {
    public:
        epicsBoolean fbool;
        epicsOctet   foctet;
        ...
        epicsFloat64 ffloat64;
        ...
        EpicsString  fstring;
        EpicsArray   darray;
        EpicsStruct  displayLimits;
   };

DbfArray

This is for array fields with a type that is not a standard epicsType, i.e. the epicsType is epicsUnknownT.

If a record definition contains: 

    struct(calcInpLink) {
        field(link,link(in))
        field(value,float64)
    }
    record(calc) extends iocRecord {
        ...
        field(inp,array(struct(calcInpLink)[]))
        ...
    }

Then the generated code contains: 

    DbfArray inp;

DbfStruct

This is for a struct field that itself has fields that are not a standard epicsType, i.e. the epicsType is epicsUnknownT.

If a record definition contains: 

    struct(calcInpLink) {
        field(link,link(in))     // NOT a standard epicsType
        field(value,float64)
    }
    record(calc) extends iocRecord {
        ...
        field(inp,struct(calcInpLink))
        ...
    }

Then the generated code contains: 

    DbfArray inp;

DbfMenu

DbfMenu> is described as: 

    class DbfMenu{
    public:
        epicsInt16    index;
        DbdMenu  *pmenuDef;
    };

If a record definition contains 

    field(fmenu,menu(name))

Then the generated header file contains 

    DbfMenu fmenu;

DbfMenu provides the current menu index and also the menu definition.

DbfEnum

DbfEnum> is described as: 

    class DbfEnum{
    public:
        epicsInt16  index;
        DbfArray  *pchoiceArray; // addr of field that is DbfArray on choices
    };

If a record definition contains 

    field(fenum,enum)

Then the generated header file contains 

    DbfEnum fenum;

pchoiceArray is the address of a field in the same record that is a DbfArray of choices.

DbfLink

DbfLink is described as 

    class DbfLink{ 
    public:
        LinkDir   dir;
        DbdLink   *plinkDef;
        EpicsStruct dataStruct;
    };

If a record definition contains 

    field(flink,link(in))

Then the generated header file contains 

    DbfLink flink;

The fields of DbfLink are initialized by locating a dbd link definition that matches the dir specified in the dbd field definition.

The fields of DbfLink are initialized as follows:

dir
This is taken from either the field definition or from the DbdLink definition and is the most restrictive. For example if one says inout and the other says in then dir will be in.
plinkDef
This is the address of the DbdLink.
dataStruct
The describes the data structure specified in the dbd link definition. It contains data used by the link support.

Note that link support always implements interface DbdLinkSupport

DbfDevice

A DbfDevice is similar to a DbfLink except that the interface implemented by the device support is also specified, i.e. instead of implementing interface DbdLinkSupport, the device support implements an interface that both record support and device support understand.


dbdStatements

The classes in dbdStatements.h allow introspection of ioc records. They describe everything defined in DBD definitions.

dbdStatements.h

// Interface is base class for an interface
class Interface {};
class InterfaceLocator {
public:
    EpicsString name;
    Interface *pinterface;
};

class StructFieldAttribute {
    EpicsString  default;
    epicsBoolean readonly;
    epicsBoolean design;
    epicsBoolean special;
    epicsBoolean dynamic;
    epicsInt16 asl;
};

class StructDbdField {
public:
    EpicsString name;
    epicsType   basic;
    dbfType     type;
    StructFieldAttribute *pattribute;
};

class DbdStruct{
public:
    EpicsString    name;
    Interface    *plifetime; // references a StructLifetime
    epicsInt16     nfields;
    StructDbdField *pfield[]; // ptr to array of ptr to StructDbdField
};

class DbdMenu{
public:
    EpicsString name;
    epicsInt16  nchoices;
    EpicsString *pchoice[];
};

class DbdLink{ //describes dbd link statement
public:
    LinkDir    dir;
    EpicsString  choiceName;
    EpicsString  dataStructName;
    Interface  *pinterface;
};

class DbdDevice { //describes dbd device statement
public:
    LinkDir   dir;
    EpicsString interfaceName;
    EpicsString choiceName;
    EpicsString dataStructName;
    Interface *pinterface;
};

// The following describes a record type
class RecordDbd { // describes a record type
    EpicsString    name;
    Interface    *plifetime; // references a RecordLifetime
    epicsInt16     nfields;
    StructDbdField *pfield[]; // ptr to array of ptr to StructDbdField
};

// The following describes a record instance
class UserDbdField {
public:
    EpicsString  name;
    epicsType    type;
    void         *pfield;
    InterfacePtr *pinterface; // userFieldHandler
};

class RecordInstance { // describes a record instance
    EpicsString  name;
    RecordDbd *pRecordDbd;
    void         *precord;     // address of record instance
    UserDbdField *puserField[];
};


Discussion of dbdStatements

StructXXX

The Struct classes describe the fields in a dbd struct or record definition. The classes are : DbdStruct, StructDbdField,and StructFieldAttribute

The fields of DbdStruct are:

name
The name of the struct.
plifetime
The address of an implementation of interface StructLifetime. The implementation is automatically generated from the dbd struct statement. See below for a description of the StructLifetime methods.
nfields
The number of fields, e.g. fields in the structure.
pfields
pointer to an array of pointers to StructDbdField.

The fields of StructDbdField are:

name
The name of the field
basic
The epicsType of the field. Unless this is epicsUnknownT generic code is usually provided for accessing the field.
type
The dbfType for the field. Note that unless basic is epicsUnknownT this has the value dbfEpicsT.
pattribute
The address of a StructFieldAttribute for the field

StructFieldAttribute has the attribute values for the field.

Menu

A dbd menu is described by class DbdMenu

The fields of DbdMenu are:

name
The menu name.
nchoices
The number of menu choices.
pchoice
The address of an array of pointers to EpicsString. Each EpicsString is a choice.

Link and Device

Each dbd link definition has an associated class DbdLink with fields:

dir
The link direction
choiceName
The name that matches a DbdLink for a DbfLink instance.
dataStructName
The class name of a DbfStruct for the Interface implementation
pinterface
The address of the Interface implementation. The interface class is DbdLinkSupport

Each dbd device definition has an associated class DbdDevice with fields:

dir
The link direction
interfaceName
The name of the interface class implemented by the device support
choiceName
The name that matches a DbdDevice for a DbfDevice instance.
dataStructName
The class name of a DbfStruct for the Interface implementation
pinterface
The address of the Interface implementation.

Record

A record type has an associated class: RecordDbd. The fields of RecordDbd are the same as fields in DbdStruct except that they refer to a record instead of a structure.

name
The name of the record.
plifetime
The address of an implementation of interface RecordLifetime. The implementation is automatically generated from the dbd record statement. See below for a description of the RecordLifetime methods.
nfields
The number of fields, e.g. fields in the record.
pfields
pointer to an array of pointers to StructDbdField. Each StructDbdField contains the name and type of the fields.
puserField
Address of an array of pointers to UserDbdField.


Record Instance

A record instance has two associated classes:UserDbdField and RecordInstance.

UserDbdField contains information for a user defined field:

name
The name of the user defined field
type
The dbfType for the field.
pfield
Address of storage for field.
pinterface
The address of an implementation of interface userFieldHandler;

The fields of RecordInstance are:

name
The name of the record instance
pRecordDbd
The address of the description of the record type
precord
The address of the record itself.
puserField
The address of a array of pointers to UserDbdField

dbdInterfaces

dbdInterfaces describes standard interfaces implemented by code that supports runtime database access.

dbdInterfaces.h

dbdInterfaces.h contains the following: 

// For struct definitions that become EpicsStruct fields
// An EpicsStructLifetime interface is automatically generated.

// For struct definitions that become DbfStruct fields
// An StructLifetime interface is automatically generated.
class StructLifetime {
public:
    virtual void allocate(DbfStruct *pDbfStruct) = 0;
    virtual bool initialize(DbfStruct *pDbfStruct) = 0;
    virtual bool finalize(DbfStruct *pDbfStruct) = 0;
    virtual void destroy(DbfStruct *pDbfStruct) = 0;
    virtual void *expose(DbfStruct *pDbfStruct, epicsInt16 index) = 0;
};

// For record definitions an RecordLifetime is automatically generated.
class RecordLifetime {
public:
    virtual void allocate(void *precord) = 0;
    virtual bool initialize(void *precord) = 0;
    virtual bool finalize(void *precord) = 0;
    virtual void destroy(void *precord) = 0;
    virtual void *expose(void *precord, epicsInt16 index) = 0;
};

// every link support module implements the following interface
class DbdLinkSupport {
public:
    virtual void report(EpicsString *errorMessage,
                     iocRecord *precord, DbfLink *pdbfLink) = 0;
    virtual bool initialize(EpicsString *errorMessage,
                     iocRecord *precord, DbfLink *pdbfLink) = 0;
    virtual bool finalize(EpicsString *errorMessage,
                     iocRecord *precord, DbfLink *pdbfLink) = 0;
    virtual bool connect(EpicsString *errorMessage,
                     iocRecord *precord, DbfLink *pdbfLink) = 0;
    virtual bool disconnect(epicsfString *errorMessage,
                     iocRecord *precord, DbffLink *pdbfLink) = 0;
    virtual bool get(EpicsString *errorMessage,
                     iocRecord *precord, DbffLink *pdbfLink,
                     dbfType type, void *pfield) = 0;
    virtual bool put(EpicsString *errorMessage,
                     iocRecord *precord, DbfLink *pdbfLink,
                     dbfType type, void *pfield) = 0;
};

/* record support implements the following*/
class RecordDbdSupport {
public:
    virtual iocRecord *allocate(EpicsString *errorMessage) = 0;
    virtual bool destroy(EpicsString *errorMessage, iocRecord *precord) = 0;
    virtual bool init(EpicsString *errorMessage,
                     iocRecord *precord, bool firstPass) = 0;
    virtual void special(iocRecord *precord, iocRecord *precord,
            bool  after,
            epicsInt16 nlevels, // number of elements in fieldIndex
            epicsInt16 fieldIndex[] // array of field indices
            ) = 0;
};

class UserFieldHandler {
public:
    virtual bool initialize(EpicsString *errorMessage,
                     iocRecord *precord,UserDbdField *puserField) = 0;
    virtual bool finalize(EpicsString *errorMessage,
                     iocRecord *precord,UserDbdField *puserField) = 0;
    virtual bool process(EpicsString *errorMessage,
                     iocRecord *precord,UserDbdField *puserField) = 0;
};

Discussion of dbdInterfaces

StructLifetime

Every dbd struct and record has an associated StructLifetime interface implementation. A tool is provided that automatically generates the implementation form the dbd definition. StructLifetime has the following fields:

allocate
Creates storage for the struct or record.
initialize
initializes the struct or record
finalize
cleans up but does not free storage
destroy
frees storage
expose
Given an index it returns the address of the storage. Note the the generated header files assign an index to each field.

DbdLinkSupport

This describes the interface implemented by link support.

RecordDbdSupport

This is the interface implemented by record support.

UserFieldHandler

This is the interface implemented by code for user extensible fields.


Class Factories

    class DbfStructFactory {
    public:
        static DbfStructLifetime *find(const char *structName);
        static void register(const char *structName,
                             DbfStructDef, *pdef);
    };
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