pthread_exit(NULL); not working

Question

This is my code for creating some threads. I want create 500 threads in the same time, not more. Easy, but my code failed after 32xxx threads created.

Then I don't understand why I get the error code 11 after 32751 threads, because, each thread ended.

I can understand, if the threads don't exit, then 32751 threads on the same computer ... but here, each thread exited.

Here is my code :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>

void *test_tcp(void *);

int main ()
    {
    pthread_t threads[500];
    int pointeur_thread;
    unsigned long compteur_de_thread=0;
    long ttt=0;
    int i;

    for(int i=0;i<=1000000;i++)
        {
        ttt++;
        pointeur_thread=pthread_create(&threads[compteur_de_thread],NULL,test_tcp,NULL);
        if (pointeur_thread!=0)
            {
            printf("Error : %d\n",pointeur_thread);
            exit(0);
            }
        printf("pointeur_thread : %d - Thread : %ld - Compteur_de_thread : %ld\n",pointeur_thread,compteur_de_thread,ttt);

        compteur_de_thread++;
        if (compteur_de_thread>=500)
            compteur_de_thread=0;
        }
    printf("The END\n");
    }

void *test_tcp(void *thread_arg_void)
    {
    pthread_exit(NULL);
    }

You are trying to create one million of threads. I would refuse if I was your OS... — Eugene Sh., Jul 21 '16 at 16:20
Possible duplicate of [Pthread\_create fails after creating several threads](http://stackoverflow.com/questions/5844428/pthread-create-fails-after-creating-several-threads) — Markus Laire, Jul 21 '16 at 16:21
This creates a helluvalot more than 500 threads at the "same time", whether you realize it or not. Further, they're all joinable, yet never joined. Either join them or create them detached. — WhozCraig, Jul 21 '16 at 16:22

score 2 · Accepted Answer · answered Jul 21 '16 at 16:21

You're probably getting the error value which corresponds to EAGAIN, which means: Insufficient resources to create another thread.

The problem is that you're not joining your threads after they exit. This could be done in the if statement where you check if all ids have been used: if (compteur_de_thread>=500).
Just loop over the array and call pthread_join on the elements of said array.

alk · Answer 2 · 2016-07-21T17:24:04.897

2

Another option besides joining the threads, would be to detach each thread. A detached thread releases all its resources the moment it ends.

To do so just call

pthread_detach(pthread_self());

inside the thread function.

If doing so, take care to also leave the program's main() by calling pthread_exit() (instead of just returning or exit()ing), as if missing to do so, main() will not just exit itself but the whole process and with this taking down all of the process' threads, which might still be running.

edited Jul 21 '16 at 17:24

answered Jul 21 '16 at 16:42

alk

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This answer should *probably* contain a warning about `exit()` or `return`ing from `main()` not being threadsafe. – EOF Jul 21 '16 at 17:19
@EOF: Yes, your are right ... ;-) sry, no comment-upvotes available to the next 7hs. – alk Jul 21 '16 at 17:26
This could cause the same problem if those threads don't manage to exit before new ones are created. – 2501 Jul 21 '16 at 17:36

score 0 · Answer 3 · answered Jul 22 '16 at 07:49

0

Thanks all.

I replace "pthread_exit(NULL);" by "pthread_detach(pthread_self());" and now is perfect.

I thought that exit means :"Close the Thread" And I thought that detach means "Thread in wait"

But no :) Thanks all.

Christophe

answered Jul 22 '16 at 07:49

christophe

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pthread_exit(NULL); not working

3 Answers3