c - Consumer/Producer with pthreads having waiting times -

i trying implement modified version of consumer/producer program code i picked on internet. follows own modifications:

   /*  *  solution producer consumer problem  *  using ptheads, mutex , condition variables  *  tanenbaum, modern operating systems, 3rd ed.  */  /*  in version buffer single number.  producer putting numbers shared buffer  (in case sequentially)  , consumer taking them out.  if buffer contains zero, indicates buffer empty.  other value valid.  */  #include <stdio.h> #include <pthread.h>  #define max 3       /* # of item  produce */ pthread_mutex_t the_mutex; pthread_cond_t condc, condp; int consumetimes[max] = { 1, 4, 3 }; int toconsume = 0;  void* producer(void *ptr) {     int i;      (i = 0; < max; i++) {         pthread_mutex_lock(&the_mutex); /* protect buffer */         /*while (buffer != 0)              /* if there in buffer wait          pthread_cond_wait(&condp, &the_mutex);*/         printf("producer: produced item %d \n", i);         toconsume++;         pthread_cond_signal(&condc); /* wake consumer */         pthread_mutex_unlock(&the_mutex); /* release buffer */         sleep(3);      }     pthread_exit(0); }  void* consumer(void *ptr) {     int i;     (i = 0; < max; i++) {         pthread_mutex_lock(&the_mutex); /* protect buffer */         while (toconsume <= 0) /* if there nothing in buffer wait */             pthread_cond_wait(&condc, &the_mutex);         sleep(consumetimes[i]);         printf("consumer: consumed item %d\n", i);         toconsume--;         //pthread_cond_signal(&condp);  /* wake consumer */         pthread_mutex_unlock(&the_mutex); /* release buffer */      }     pthread_exit(0); }  int main(int argc, char **argv) {     pthread_t pro, con;      // initialize mutex , condition variables     /* what's null ??? */     pthread_mutex_init(&the_mutex, null);     pthread_cond_init(&condc, null); /* initialize consumer condition variable */     pthread_cond_init(&condp, null); /* initialize producer condition variable */      // create threads     pthread_create(&con, null, consumer, null);     pthread_create(&pro, null, producer, null);      // wait threads finish     // otherwise main might run end     // , kill entire process when exits.     pthread_join(&con, null);     pthread_join(&pro, null);      // cleanup -- happen automatically @ end of program     pthread_mutex_destroy(&the_mutex); /* free the_mutex */     pthread_cond_destroy(&condc); /* free consumer condition variable */     pthread_cond_destroy(&condp); /* free producer condition variable */  } 

here's want do:

basically, each item has consume , production time.

the consume times indicated each item in consumetimes array.

so, example consumetimes[0] = 1 means consuming 1st item should take single time unit.

for production, use constant time value, sleep(3), producing every item should take 3 time units.

when run code, following output time:

producer: produced item 0  consumer: consumed item 0 producer: produced item 1  consumer: consumed item 1 producer: produced item 2  consumer: consumed item 2 

however, considering production , consume times should this:

producer: produced item 0 (t=0) consumer: consumed item 0 (t=1) producer: produced item 1 (t=3) producer: produced item 2 (t=6) consumer: consumed item 1 (t=7) consumer: consumed item 2 (t=9) 

in short, producer must produce new item in every 3 time intervals. in case, seems waiting on consumer finish , can't seem figure out why.

the consumer holds mutex whole time waiting , not allow producer run.

change consuming loop follows

    pthread_mutex_lock(&the_mutex); /* protect buffer */     while (toconsume <= 0) /* if there nothing in buffer wait */         pthread_cond_wait(&condc, &the_mutex);     pthread_mutex_unlock(&the_mutex); /* release buffer */      sleep(consumetimes[i]);      pthread_mutex_lock(&the_mutex); /* protect buffer */     printf("consumer: consumed item %d\n", i);     toconsume--;     pthread_mutex_unlock(&the_mutex); /* release buffer */ 

and you'll receive expected result.