TIP #128: Ability to Install a Custom Memory Allocator

Title:Ability to Install a Custom Memory Allocator
Version:$Revision: 1.5 $
Authors: Christophe Cap <udragon at users dot sourceforge dot net>
Mike Jackson <hhyJackson1275 at who-got-mail dot com>
Created:Thursday, 13 March 2003


This TIP alters Tcl to allow embedded uses of the Tcl library (and any extensions) to either use the Tcl memory allocators as their main allocator (especially in C++) or to set the memory allocator that Tcl uses for itself through ckalloc().


A while ago I was experiencing troubles when allocating images ([image create photo]) while memory was already exhausted, my app crashed (due to known bug item #698571, which is in the HEAD by now!) This shouldn't happen anyway since my application had it's new handler set.

Tracing down the source of the allocators I noticed that Tcl uses HeapAlloc() (on Win32) to allocate its memory. Why not use malloc()?

New/Malloc Handler

It would be nice to be able to catch memory allocation errors with a custom new handler.

A solution could be to replace HeapAlloc() (on Win32) and other platform specific memory handlers should be replaced by malloc().

This way a new handler can by set through set_new_handler().

Note that the Microsoft VC++ compiler has some ANSI incompatibility in that it uses _set_new_handler() rather than set_new_handler(). We would naturally conceal this platform difference.

For example:

#include <new> 

// New handler for Microsoft Visual C++ compiler

#ifdef _MSC_VER
#include <new.h>

int __cdecl _newHandler(size_t size )
   // Do whatever

   return 0;


// Ansi C/C++ new handler

void __cdecl _newHandler( void )
   // Do whatever

void sethandlers(void)
// Microsoft compiler 
#ifdef _MSC_VER  

   _set_new_handler (_newHandler); // Setup new handler
   _set_new_mode( 1 ); // Re-route malloc failures to new handler !

// Ansi compiler 


   set_new_handler (_newHandler); // ANSI new handler


Tcl Implementation

The above suggested solution could work for some compilers, but may not for all (some compilers might not support setting a malloc failure callback.) Therefore a Tcl custom new handler functionality could be implemented that handles Tcl specific memory allocation failures.

Something like: Tcl_SetMemHandler()?


This document has been placed in the public domain.

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