On Thu, Aug 16, 2012 at 11:48:35AM +0200, Richard Braun wrote:
> On Wed, Aug 15, 2012 at 05:47:47PM -0700, Thomas DiModica wrote:
> > My understanding is that pthread_cond_wait is a cancellation point.
> > It achieves this by entering asynchronous cancellation mode before blocking.
> >
> > I don't see, however, any code that checks for a pending cancellation when
> > we enter the function. As far as I can tell, the implementation is that
> > pthread_cond_wait is a cancellation point if and only if the thread is
> > canceled while it is blocked.
>
> It seems so, yes.
This tiny test shows the bug :
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int predicate;
int cancelled;
static void *
run(void *arg)
{
printf("spin until cancellation is sent\n");
while (!cancelled)
sched_yield();
printf("waiting for predicate\n");
pthread_mutex_lock(&mutex);
while (!predicate)
pthread_cond_wait(&cond, &mutex);
pthread_mutex_unlock(&mutex);
printf("exiting thread\n");
return NULL;
}
int
main(int argc, char *argv[])
{
pthread_t thread;
pthread_create(&thread, NULL, run, NULL);
printf("sending cancellation\n");
pthread_cancel(thread);
cancelled = 1;
printf("joining thread\n");
pthread_join(thread, NULL);
return EXIT_SUCCESS;
}
--
Richard Braun
