TIP #128: Ability to Install a Custom Memory Allocator

[Christophe Cap]

TIP #128: ABILITY TO INSTALL A CUSTOM MEMORY ALLOCATOR
========================================================
Version: $Revision: 1.1 $
Author: Christophe Cap <udragon_at_users.sourceforge.net>
State: Draft
Type: Project
Tcl-Version: 8.5
Vote: Pending
Created: Thursday, 13 March 2003
URL: http://purl.org/tcl/tip/128.html
WebEdit: http://purl.org/tcl/tip/edit/128
Post-History:

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ABSTRACT
==========

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()_.

BACKGROUND
============

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;
}

#else

//
// Ansi C/C++ new handler
//

void __cdecl _newHandler( void )
{
// Do whatever
}
#endif

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

#else

set_new_handler (_newHandler); // ANSI new handler

#endif
}

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()_?

COPYRIGHT
===========

This document has been placed in the public domain.

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