[GNUnet-developers] threads & deadlocks

[Jussi Eloranta]

Hello,

I have been experiencing deadlocks with gnunet-gtk on macos x.
This happens during searches where one gets many replies.

After some heuristic debugging, I found that the following change in
util/semaphore.c resolved the problem (look at the comment line):

int semaphore_up_(Semaphore * s,
                  const char * filename,
                  const int linenumber) {
  int value_after_op;
  pthread_cond_t * cond;

  GNUNET_ASSERT_FL(s != NULL, filename, linenumber);
  cond = s->cond;
#if DEBUG_SEMUPDOWN
  LOG(LOG_DEBUG,
      "semaphore_up %p enter at %s:%d\n",
      s,
      filename,
      linenumber);
#endif
  MUTEX_LOCK(&(s->mutex));
  (s->v)++;
  value_after_op = s->v;
  /* The lines below were originally in opposite order */
  GNUNET_ASSERT(0 == pthread_cond_signal(cond));
  MUTEX_UNLOCK(&(s->mutex));

#if DEBUG_SEMUPDOWN
  LOG(LOG_DEBUG,
      "semaphore_up %p exit at %s:%d\n",
      s,
      filename,
      linenumber);
#endif
  return value_after_op;
}

After this change it works (look at the comment line in the code). I 
don't immediately see why this would
change anything but in practice it does... Or may be it enforces that 
signal and wait calls will "match"?


Best regards,

Jussi Eloranta