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Re: [Help-glpk] xmalloc, thread-safety

From: François Galea
Subject: Re: [Help-glpk] xmalloc, thread-safety
Date: Fri, 31 Aug 2007 16:34:26 +0200
User-agent: IceDove (X11/20070329)

Andrew Makhorin a écrit :
I am trying to run GLPK in multi-thread way, but I discovered, that
there is a problem with memory allocation/deallocation.

 I modified the library code:

void    *xmalloc(int size) {
        return calloc(1, size);

I am personally using self-made parallel branch-and-bound code, and had to make equivalent modifications when using POSIX threads.

To make glpk thread-safe you need to provide two platform-specific
routines lib_set_ptr and lib_get_ptr (see src/glplib03.c). By default
these routines store a pointer in the static memory, and currently
only a version for the windows dll is implemented.

I already did such using POSIX threads, using the pthread_key_create and pthread_setspecific calls. One problem remains though: a thread can not call glp_delete_prob on a LP that has been allocated by another thread. Using malloc/free, this is perfectly possible.

Thus, it is quite difficult to maintain a pool of B&B nodes which can be handled in the same way by all the threads.

François Galea
Equipe OPALE - Laboratoire PRiSM
Université de Versailles-Saint Quentin en Yvelines
45 av Etats-Unis F-78035 Versailles CEDEX
Tél. : +33 1 39 25 40 50

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