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POSIX Dead lock

Posted on 2007-03-23
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Last Modified: 2011-09-20
Hey guys, im just trying to create 10 threads which then i want to print out in backwards order... so
"from thread 10", "from thread 9" ---> "from thread 1"

But im getting deadlocked after i get "from thread 10" to print.... Any ideas?

#include <stdio.h>
#include <sys/types.h>
#include <pthread.h>

pthread_mutex_t mlock;
pthread_cond_t conditions[10];

int count = 10;


void * func(void * arg)
{
   int index = (int)arg - 1;

   pthread_mutex_lock(&mlock);

      while(count != (int)arg)
         pthread_cond_wait(&conditions[index], &mlock);

      printf("from thread %d\n", (int)arg);
      count--;
      index--;

      pthread_cond_signal(&conditions[index]);

    pthread_mutex_unlock(&mlock);

    return (NULL);
}


int main(int argc, char* argv[]) {
    int n,i;
    pthread_t threads[count];
    pthread_mutex_init(&mlock, NULL);

    for (i = 0; i < count; i++) {
      pthread_create(&threads[i], NULL, func, (void*)i+1);
      pthread_cond_init(&conditions[i], NULL);
    }

    for (i = 0; i < count; i++) {
      pthread_join(threads[i], NULL);
    }

    exit(1);
}
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Question by:intazaar
2 Comments
 
LVL 15

Accepted Solution

by:
efn earned 500 total points
ID: 18787423
I don't know if this is the problem, but I can tell you one thing that looks fishy.

A thread might use a condition variable before it has been initialized.  Specifically, after a thread is started, it could easily get to the pthread_cond_wait call before the main thread has called pthread_cond_init.  This is not the order you want.

You could try moving the call to pthread_cond_init before the call to pthread_create and see if that helps.
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Author Comment

by:intazaar
ID: 18787510
Thx mate, that was exactly it. Runs like a dream!
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