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Date: Tue, 06 Jul 2010 20:41:38 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai-help] Mixing skin calls (cancellation points)
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To: Steve Deiters <SteveDeiters@domain.hid>
Cc: xenomai@xenomai.org

Steve Deiters wrote:
> Is it in general valid to mix calls from different skins?  In
> particular, can I expect the native skin calls to work as POSIX
> cancellation points?  For example, if I have a POSIX thread with a
> pthread_t identifier which I know calls rt_cond_wait somewhere, will it
> work as a cancellation point when I call pthread_cancel?
> 
> The example program attached will not cancel if I have CANCEL_DEFERRED
> defined as 1 at the top, which sets the cancel type to deferred.  This
> is on a PowerPC with Xenomai 2.5.3.  I think this worked with Xenomai
> 2.4.10.
> 
> 
> --------
> 
> 
> #include <stdio.h>
> #include <errno.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <pthread.h>
> #include <native/task.h>
> #include <native/cond.h>
> 
> #define CANCEL_DEFERRED 1
> 
> RT_MUTEX mutex;
> RT_COND cond;
> pthread_t thread;
> 
> void *entry(void *cookie)
> {
>    fprintf(stderr, "Starting thread\n");
> 
> #if CANCEL_DEFERRED
>    pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, NULL);
> #else
>    pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
> #endif
> 
>    rt_mutex_acquire(&mutex, TM_INFINITE);
>    rt_cond_wait(&cond, &mutex, TM_INFINITE);
>    rt_mutex_release(&mutex);
> 
>    return NULL;
> }

This program would also deadlock with plain POSIX: you are missing a
cleanup handler which releases the mutex.

-- 
					    Gilles.