Question

I have two threads. First one is something like this:

while(1)
{
   pthread_mutex_lock(&mutex);
   //DO WORK
   pthread_mutex_unlock(&mutex);
   pthread_yield();
}

The second one locks the mutex on user event, change some settings and unlocks. Thread one does ~ 200 iterations a second. However on occasion it takes the second thread up to 3 seconds to get active (to lock the mutex). How do I ensure faster response?

EDIT- second thread:

while(1)
{
   waitForUserInput(); // blocking call to linux input
   pthread_mutex_lock(&mutex);
   // Change some settings which are used by the first thread
   pthread_mutex_unlock(&mutex);
}

EDIT2 – Fixed the question (“to unlock the mutex” -> “to lock the mutex”).

Answer 1

Try changing pthread_yield() to usleep(10) or usleep(100) to determine if the yield is causing you problems, as I’ve seen cases where yield does nothing, which would cause your loop to unlock and relock a too quickly for the first thread to catch its lock most of the time. Then you might consider looking at condition variables in pthread if you want more control.