Unstable of semaphore

sem_t w,r,s1,s2,s3;
pthread_mutex_t m;


int main(int argc, char* argv[])
{
  
   mutex and semaphores initialization .....

   call threads....

   wait until finish and cancel threads...
   
   clean threads and semaphores

   <em>exit;</em>
}



void *reader(void *argv)
{
   
   while(TRUE)
   {
      sem_wait(&r);
      sem_wait(&s1);
      pthread_mutex_lock(&m);
      
      ... read data.....

      pthread_mutex_unlock(&m);
      sem_post(&s1);
      sem_post(&w);   
   } 
   printf("Done read\n");
   sem_post(&extra2);
   pthread_exit(NULL);
}

void *writer(void *argv)
{
   
   while(TRUE)
   {
     sem_wait(&w);
     sem_wait(&s1);
     pthread_mutex_lock(&m);
     
    
     pthread_mutex_unlock(&m);
     sem_post(&s1);
     sem_post(&r);
   }
   printf("Done Write\n");
   sem_post(&s3);
   pthread_exit(NULL);
}

I wrote a reader/writer issue and now it's writing the same as from the source ... but sometime it become unstable and making output wrong or stop working.. Can someone plz show me the unstable part? if need, i'll also provide my code. Thanks in advance..

smith32

Newbie Poster

18 posts since Jul 2009

Reputation Points: 10

Solved Threads: 1

3 Months Ago

Post the code or just a part of code. Which compiler are you using? Try to compile it step by step for 5-8 times and you will get to know, which part is guilty :-)

sem_t w,r,s1,s2,s3; pthread_mutex_t m; int main(int argc, char* argv[]) { mutex and semaphores initialization ..... call threads.... wait until finish and cancel threads... clean threads and semaphores <em>exit;</em> } void *reader(void *argv) { while(TRUE) { sem_wait(&r); sem_wait(&s1); pthread_mutex_lock(&m); ... read data..... pthread_mutex_unlock(&m); sem_post(&s1); sem_post(&w); } printf("Done read\n"); sem_post(&extra2); pthread_exit(NULL); } void *writer(void *argv) { while(TRUE) { sem_wait(&w); sem_wait(&s1); pthread_mutex_lock(&m); pthread_mutex_unlock(&m); sem_post(&s1); sem_post(&r); } printf("Done Write\n"); sem_post(&s3); pthread_exit(NULL); }

Abhineet.Ayan

Newbie Poster

4 posts since Feb 2012

Reputation Points: 10

Solved Threads: 0

This article has been dead for over three months

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