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

[François Galea]

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
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