Search code examples
cmultithreadingpthreadsterminate

C - Waiting For Multiple Threads to Terminate

I am trying to wait for all the threads to terminate before the main() process terminates. Here is what I have so far:

void* mapperFunction()
{
    printf("Hello\n");
    return NULL;
}
int main()
{
    int i; // Used in "for" loops.
    int N = 3; 
    pthread_t* mapperThreads = (pthread_t*) malloc(sizeof(pthread_t) * N);
    for ( i = 0; i < N; i++)
    { // Creates all the mapper threads.
        pthread_create( &mapperThreads[N], NULL, mapperFunction, NULL);
    }
    for ( i = 0; i < N; i++)
    { // Waits for all the mapper threads to terminate.
        pthread_join( mapperThreads[N],NULL);
    }
    return 0;
}

I get three different outputs when I run this code;

1- Hello\n

2- Helle\nHello\n

3- Hello\nHello\nHello\n

It looks like the main() process does not always wait for all threads to terminate. What am I doing wrong?

Solution

  • You want &mapperThreads[i] instead of &mapperThreads[N] in each case.