Handles
Handles
NAMESYNOPSIS
DESCRIPTION
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.
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