Tcl8.6.10/Tk8.6.10 Documentation > [incr Tcl] Package C API, version 4.2.0 > Preserve

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Itcl_Alloc, Itcl_Free, Itcl_PreserveData, Itcl_ReleaseData, Itcl_EventuallyFree — Manipulate an Itcl list object.


#include <itcl.h>

void *



Itcl_EventuallyFree(ptr, fproc)



size_t size (in)
Number of bytes to allocate.

void *ptr (in)
Pointer value allocated by Itcl_Alloc.

Tcl_FreeProc *fproc (in)
Address of function to call when the block is to be freed.


These procedures are used to allocate and release memory, especially blocks of memory that will be used by multiple independent modules. They are similar in function to the routines in the public Tcl interface, Tcl_Alloc, Tcl_Free, Tcl_Preserve, Tcl_Release, and Tcl_EventuallyFree. The Tcl routines suffer from issues with performance scaling as the number of blocks managed grows large. The facilities of Itcl encounter these performance scaling issues and require an alternative that does not suffer from them.

Itcl_Alloc returns an untyped pointer to an allocated block of memory of at least size bytes. All size bytes are initialized to zero.

A module calls Itcl_PreserveData on a pointer ptr allocated by Itcl_Alloc to prevent deallocation of that memory while the module remains interested in it.

A module calls Itcl_ReleaseData on a pointer ptr previously preserved by Itcl_PreserveData to indicate the module no longer has an interest in the block of memory, and will not be disturbed by its deallocation.

Itcl_EventuallyFree is called on a pointer ptr allocated by Itcl_Alloc to register a deallocation routine fproc to be called when the number of calls to Itcl_ReleaseData on ptr matches the number of calls to Itcl_PreserveData on ptr. This condition indicates all modules have ended their interest in the block of memory and a call to fproc with argument ptr will deallocate the memory that no module needs anymore.

Itcl_Free is a deallocation routine for a ptr value allocated by Itcl_Alloc. It may be called on any ptr with no history of an Itcl_PreserveData call unmatched by an Itcl_ReleaseData call. It is best used as an fproc argument to Itcl_EventuallyFree or as a routine called from within such an fproc routine. It can also be used to deallocate a ptr value when it can be assured that value has never been passed to Itcl_PreserveData or Itcl_EventuallyFree.


free, memory
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