Question

My daemon initializes itself in four different threads before it starts doing its things. Right now I use a counter which is incremented when a thread is started and decremented when it is finished. When the counter hits 0 I call the initialization finished callback.

Is this the preferred way to do it, or are there better ways? I’m using POSIX threads (pthread) and I just run a while cycle to wait for the counter to hit 0.

Edit: pthread_barrier_* functions are not available on my platform although they do seem to be the best choice.

Edit 2: Not all threads exit. Some initialize and then listen to events. Basically the thread needs to say, “I’m done initializing”.

Answer 1

Rather than spinning, use the pthread mutex/condvar primitives. I’d suggest a single mutex to protect both the count of threads outstanding, and the condvar.

The main loop looks like this:

acquire mutex
count=N_THREADS;
start your N threads
while (1) {
  if (count==0) break;
  cond_wait(condvar);
}
release mutex

And when each thread is ready it would do something like this:

acquire mutex
count--
cond_signal(condvar)
release mutex

(EDIT: I have assumed that the threads are to keep going once they have done their initialisation stuff. If they are to finish, use pthread_join as others have said.)