C pthread synchronize function

问题:

Is there a function in pthread library to synchronize threads? Not mutexes, not semaphores, just one call function. It is supposed to lock the threads that get in that point until all the threads reach such function. E.g:

function thread_worker(){
    //hard working

    syncThreads();
    printf("all threads are sync\n");
}

So the printf is called only when all the threads end the hard working.

回答1:

The proper way to do this would be with a barrier. pthread supports barriers using pthread_barrier_t. You initialize it with the number of threads that will need to sync up, and then you just use pthread_barrier_wait to make those threads sync up.

Example:

pthread_barrier_t barr;

void thread_worker() {
    // do work
    // now make all the threads sync up
    int res = pthread_barrier_wait(&barr);
    if(res == PTHREAD_BARRIER_SERIAL_THREAD) {
        // this is the unique "serial thread"; you can e.g. combine some results here
    } else if(res != 0) {
        // error occurred
    } else {
        // non-serial thread released
    }
}


int main() {
    int nthreads = 5;
    pthread_barrier_init(&barr, NULL, nthreads);

    int i;
    for(i=0; i<nthreads; i++) {
        // create threads
    }
}