[lttng-dev] Tracepoints for pthreads conditional variables

[Shehab Elsayed]

Hi,

I am trying to create wrappers for pthreads conditional variables functions
(wait, signal and broadcast) to insert tracepoints. I followed the same
approach done for the mutex functions already provided with lttng, however
I am running into some problems. Mainly the applications seem to get stuck
when the conditional variable wrappers are enabled.

Here is my implementation for the wrapper functions:
int pthread_cond_wait(pthread_cond_t *condition, pthread_mutex_t
*mutex)

{

  static int (*cond_wait)(pthread_cond_t *, pthread_mutex_t
*);
  int retval;



  if (!cond_wait)
{

    cond_wait = dlsym(RTLD_NEXT, "pthread_cond_wait");

    if (!cond_wait)
{

      if (thread_in_trace)
{


abort();


}

      fprintf(stderr, "unable to initialize pthread wrapper
library.\n");
      return EINVAL;


}


}

  if (thread_in_trace)
{

    return cond_wait(condition, mutex);


}



  thread_in_trace =
1;

  tracepoint(lttng_ust_pthread, pthread_cond_wait_begin, condition,
mutex,

    LTTNG_UST_CALLER_IP());

  retval = cond_wait(condition, mutex);

  tracepoint(lttng_ust_pthread, pthread_cond_wait_end, condition,
mutex,

    LTTNG_UST_CALLER_IP());

  thread_in_trace =
0;

  return retval;

}



int pthread_cond_signal(pthread_cond_t
*condition)

{

  static int (*cond_signal)(pthread_cond_t
*);

  int retval;



  if (!cond_signal)
{

    cond_signal = dlsym(RTLD_NEXT, "pthread_cond_signal");

    if (!cond_signal)
{

      if (thread_in_trace)
{


abort();


}

      fprintf(stderr, "unable to initialize pthread wrapper
library.\n");
      return EINVAL;


}


}

  if (thread_in_trace)
{

    return cond_signal(condition);


}



  thread_in_trace =
1;

  tracepoint(lttng_ust_pthread, pthread_cond_signal_begin,
condition,
    LTTNG_UST_CALLER_IP());

  retval = cond_signal(condition);

  tracepoint(lttng_ust_pthread, pthread_cond_signal_end,
condition,
    LTTNG_UST_CALLER_IP());

  thread_in_trace =
0;

  return retval;

}



int pthread_cond_broadcast(pthread_cond_t
*condition)

{

  static int (*cond_broadcast)(pthread_cond_t
*);
  int retval;



  if (!cond_broadcast)
{

    cond_broadcast = dlsym(RTLD_NEXT, "pthread_cond_broadcast");

    if (!cond_broadcast)
{

      if (thread_in_trace)
{


abort();


}

      fprintf(stderr, "unable to initialize pthread wrapper
library.\n");
      return EINVAL;


}


}

  if (thread_in_trace)
{

    return cond_broadcast(condition);


}



  thread_in_trace =
1;

  tracepoint(lttng_ust_pthread, pthread_cond_broadcast_begin,
condition,
    LTTNG_UST_CALLER_IP());

  retval = cond_broadcast(condition);

  tracepoint(lttng_ust_pthread, pthread_cond_broadcast_end,
condition,
    LTTNG_UST_CALLER_IP());

  thread_in_trace =
0;

  return retval;

}

Things I have tried:
1- Comment out pthread_cond_wait function --> segmentation fault
2- Comment out pthread_cond_signal and _broadcast --> stuck (I can see the
program is still running but nor forward progress is being made) compared
to the case when the wrappers are not preloaded.
3- Comment out all tracepoint related code (basically the wrapper just call
the corresponding pthreads function) --> same results as points 1 and 2.

Any idea what might be causing this or how I could debug this problem?

Thank you very much in advance.

Best Regards,
Shehab
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