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
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;
}
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