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Mutex unlock from different thread?

+4 votes
284 views

There are two threads one takes lock and execute infinite loop. When ever other thread start execution before trying to take lock it unlocks the mutex.

Its a wrong behavior, how can I prevent this.

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

pthread_t callThd_one, callThd_two;
pthread_mutex_t mutexsum;

void *thread_one(void *arg)
{
   pthread_mutex_lock (&mutexsum);
   while(!sleep(1))
       printf("\n In thread One \n");

   pthread_mutex_unlock (&mutexsum);
   pthread_exit((void*) 0);
}

void *thread_two(void *arg)
{
   pthread_mutex_unlock (&mutexsum);
   //pthread_mutex_lock (&mutexsum);
   while(!sleep(1))
       printf("\n In thread two \n");

   pthread_mutex_unlock (&mutexsum);
   pthread_exit((void*) 0);
}

int main (int argc, char *argv[])
{
   void *status;
   pthread_attr_t attr;

   pthread_mutex_init(&mutexsum, NULL);

   pthread_attr_init(&attr);
   pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

   pthread_create(&callThd_one, &attr, thread_one, NULL);
   pthread_create(&callThd_two, &attr, thread_two, NULL);

   pthread_attr_destroy(&attr);

   pthread_join(callThd_one, &status);
   pthread_join(callThd_two, &status);

   pthread_mutex_destroy(&mutexsum);
   pthread_exit(NULL);
}

Is there any way to sure that mutex should be unlock only by the thread which took lock.

posted Oct 14, 2013 by Vikas Upadhyay

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1 Answer

+1 vote

This is incorrect way of mutex handling. This problem can be solved two ways

  1. instead trying pthread_mutex_unlock and pthread_mutex_lock one should use pthread_mutex_trylock to avoid deadlock scenarios
  2. if want to continue with same code use error checking mutex rather default.
answer Oct 18, 2013 by Pankaj Agarwal
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