pthread_cancel() problems

["Kevin D. Clark" <kclark at cabletron dot com>]

Hi,

Is anybody else successfully using pthread_cancel() with this library?

I can't seem to get it to work, and I haven't been able to track down
the cause of the problem yet.  I'm not using asynchronous cancelation
either.

At the end of this mail I will include another test program that
shows off this problem.  If the program ran correctly then you'd see a
stream of increasing numbers on your screen.  However, since the
cleanup routine (associated with pthread_cleanup_push()) is never
called, the counter remains at zero.

So I strongly suspect that there's a bug in the library here.  I just
wish I could find it.

--kevin

PS  The program works as expected on a Solaris 2.6 box.


/*  Compiling this program as a C or C++ program doesn't seem to have
 *  an effect on the fact that calling pthread_cancel() doesn't cause
 *  the canceledRoutine() to be invoked.
 *
 *  Environment:  VC++ 6.x, NT 4.x, service pack 5
 *                Pthreads-win32 snapshot 1999-11-02
 */

#include <stdio.h>
#include <errno.h>
#ifdef __unix
#include <unistd.h>
#endif

#include <pthread.h>

void *canceledRoutine(void *);
static volatile int counter = 0; /* volatile thrown in out of desperation */
pthread_t canceledThread;

pthread_mutex_t mu = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cv = PTHREAD_COND_INITIALIZER;
static int okToCancel = 0;

int
main(int argc, char *argv[])
{
  int i = 0;
  pthread_attr_t tattr;

  pthread_attr_init(&tattr);
  pthread_attr_setdetachstate(&tattr, PTHREAD_CREATE_DETACHED);

  for (i=0; i<100; i++) {
    /*    fprintf(stderr, "iteration %d\n", i); */
    pthread_create(&canceledThread, &tattr, canceledRoutine, (void *)i);

    pthread_mutex_lock(&mu);
    while (! okToCancel) {
      int result;
      result = pthread_cond_wait(&cv, &mu);
      if (result == EINTR) {
        fprintf(stderr, "%s:%d: interupted!\n", __FILE__, __LINE__);
      }
    }
    pthread_mutex_unlock(&mu);

    /* at this point we know that the other thread has pushed a cleanup
       handler onto its stack */
    pthread_cancel(canceledThread);

    okToCancel = 0;
    
    fprintf(stderr, "counter is %d\n", counter);
  }
  
  return 0;
}

void cancelCleanup(void *arg)
{
  int i = (int)arg;
  counter++;
  fprintf(stderr, "%d -- Hey, I've been canceled!\n", i);
}


void *
canceledRoutine(void *arg)
{
  int i = (int)arg;
  int ignored;
  
  /*
   *  My understanding is that the default is for deferred
   *  cancelation, but I'll do this anyways here just to be absolutely
   *  sure.
   */
  if (pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &ignored) != 0) {
    fprintf(stderr, "problem with pthread_setcanceltype()\n";
  }
  
  pthread_cleanup_push(cancelCleanup, (void *)i);
  pthread_mutex_lock(&mu);
  okToCancel = 1;
  pthread_mutex_unlock(&mu);
  pthread_cond_signal(&cv);
  
  while(1) {
#ifdef __unix
    /* sleep() is defined to be a cancelation point */
    sleep(1);
#else
    /*  I'm not totally sure what is defined to be a cancelation point.
     *  Perhaps this needs to be documented?
     */
    Sleep(1000);
#endif
  }
  
  pthread_cleanup_pop(0);
  
  return 0;
}