Handles(TCL)

NAME
Tcl_HandleAlloc, Tcl_HandleFree, Tcl_HandleTblInit, Tcl_HandleTblRelease, Tcl_HandleTblUseCount, Tcl_HandleWalk, Tcl_HandleXlate - Dynamic, handle addressable tables.

SYNOPSIS

#include <tclExtend.h>
void_pt
Tcl_HandleTblInit (const char *handleBase,
                   int         entrySize,
                   int         initEntries);
int
Tcl_HandleTblUseCount (void_pt  headerPtr,
                       int      amount);
void
Tcl_HandleTblRelease (void_pt headerPtr);
void_pt
Tcl_HandleAlloc (void_pt   headerPtr,
                 char     *handlePtr);
void_pt
Tcl_HandleXlate (Tcl_Interp *interp,
                 void_pt     headerPtr,
                 const char *handle);
void_pt
Tcl_HandleWalk (void_pt   headerPtr,
                int      *walkKeyPtr);
void
Tcl_WalkKeyToHandle (void_pt   headerPtr,
                     int       walkKey,
                     char     *handlePtr);
void
Tcl_HandleFree (void_pt headerPtr,
                void_pt entryPtr);

DESCRIPTION

The Tcl handle facility provides a way to manage table entries that may be referenced by a textual handle from Tcl code. This is provided for applications that need to create data structures in one command, return a reference (i.e. pointer) to that particular data structure and then access that data structure in other commands. An example application is file handles.

A handle consists of a base name, which is some unique, meaningful name, such as `file' and a numeric value appended to the base name (e.g. `file3'). The handle facility is designed to provide a standard mechanism for building Tcl commands that allocate and access table entries based on an entry index. The tables are expanded when needed, consequently pointers to entries should not be kept, as they will become invalid when the table is expanded. If the table entries are large or pointers must be kept to the entries, then the the entries should be allocated separately and pointers kept in the handle table. A use count is kept on the table. This use count is intended to determine when a table shared by multiple commands is to be release.

  Tcl_HandleTblInit
Create and initialize a Tcl dynamic handle table. The use count on the table is set to one.

Parameters:
    o handleBase - The base name of the handle, the handle will be returned in the form "baseNN", where NN is the table entry number.
    o entrySize - The size of an entry, in bytes.
    o initEntries - Initial size of the table, in entries.

Returns:
    A pointer to the table header.

  Tcl_HandleTblUseCount

Alter the handle table use count by the specified amount, which can be positive or negative. Amount may be zero to retrieve the use count.

Parameters:
    o headerPtr - Pointer to the table header.
    o amount - The amount to alter the use count by.

Returns:
    The resulting use count.

  Tcl_HandleTblRelease

Decrement the use count on a Tcl dynamic handle table. If the count goes to zero or negative, then release the table.

Parameters:
    o headerPtr - Pointer to the table header.

  Tcl_HandleAlloc

Allocate an entry and associate a handle with it.

Parameters:
    o headerPtr - A pointer to the table header.
    o handlePtr - Buffer to return handle in. It must be big enough to hold the name.

Returns:
    A pointer to the allocated entry (user part).

  Tcl_HandleXlate

Translate a handle to a entry pointer.

Parameters:
    o interp - A error message may be returned in result.
    o headerPtr - A pointer to the table header.

    o handle - The handle assigned to the entry.

Returns:
    A pointer to the entry, or NULL if an error occurred.

  Tcl_HandleWalk

Walk through and find every allocated entry in a table. Entries may be deallocated during a walk, but should not be allocated.

Parameters:
    o headerPtr - A pointer to the table header.
    o walkKeyPtr - Pointer to a variable to use to keep track of the place in the table. The variable should be initialized to -1 before the first call.
Returns:
    A pointer to the next allocated entry, or NULL if there are not more.

  Tcl_WalkKeyToHandle

Convert a walk key, as returned from a call to Tcl_HandleWalk into a handle. The Tcl_HandleWalk must have succeeded.

Parameters:
    o headerPtr - A pointer to the table header.
    o walkKey - The walk key.
    o handlePtr - Buffer to return handle in. It must be big enough to hold the name.

  Tcl_HandleFree

Frees a handle table entry.

Parameters:
    o headerPtr - A pointer to the table header.
    o entryPtr - Entry to free.