#include<stdio.h>
#include<pthread.h>
#include<stdlib.h>
static pthread_cond_t cond=PTHREAD_COND_INITIALIZER; /*statically
initialize the condition variable *cond* */
static pthread_mutex_t mtx=PTHREAD_MUTEX_INITIALIZER;/*statically
initialize the mutex *mtx* */
static int prod=0;
static int basic=100;
static int actual_prod=250;
static int temp;
void * producer() /*producer thread */
{
int i;
temp=actual_prod; /*store the actual_prod value in temp coz we are gonna
change actual_prod in consumer */
for(i=1;i<=temp;i++)
{
pthread_mutex_lock(&mtx); /*lock the mutex */
prod++;
pthread_mutex_unlock(&mtx);/*unlock the mutex*/
if(prod==basic) /*if producer has produced *basic* units , send a signal
to consume */
{
printf("producer produced %d units\n",prod);
pthread_cond_signal(&cond); /*send a signal , so that
pthread_cond_wait() returns and consumer will be able to consume */
}
/*suppose , u wanna produce 250 units or 50 units , in that case consumer
should be still able to consume everything,
lets assume actual_prod=50, then at this point prod=50 ,actual_prod=50 ,
basic=100...condition satisfies so send a signal . If actual_prod is 250, for
understanding this case check consumer thread*/
else if((prod==actual_prod) && (actual_prod < basic))
{
printf("producer produced %d units\n",actual_prod);
pthread_cond_signal(&cond);
}
}//for
printf("prod=%d\n",prod); /*print the final value of prod
...should be zero ie all produced units must be consumed */
exit(1); /*terminates all threads */
}
void *consumer()
{
for(;;){
pthread_mutex_lock(&mtx); /*lock the mutex */
/*for actual_prod =100 , by the time pthread_cond_wait() receives a signal
, prod will be 100..so wont wait */
/*Assume , that context switch occurs when prod =90 , but actual_prod=200,
then it will wait */
/*but take for ex , prod=90 but actual_prod is also 90, then it wont wait
coz second condition will be false*/
while((prod!=basic) && (prod!=actual_prod))
pthread_cond_wait(&cond,&mtx);
if(actual_prod<basic) /* to consume the left out units produced for ex
, if actual_prod is 250 ,then the last 50 units */
{
printf("consumer consumed %d units\n",prod);
prod=prod-actual_prod;
actual_prod-=prod; /*this is for decrementing the value of actual_prod ,
used when actual_prod is greater than basic , but is not a multiple of basic .
for ex actual_prod = 350*/
}
else if (prod == basic){ /* when actual_prod is a multiple of basic */
printf("consumer consumed %d units\n",prod);
prod=prod-basic;
actual_prod-=basic;
}
else
continue;
pthread_mutex_unlock(&mtx); /*explicitly unlock the mutex */
}
}
int main()
{
pthread_t t1,t2;
int status;
status=pthread_create(&t1,NULL,consumer,NULL);
status=pthread_create(&t2,NULL,producer,NULL);
pthread_join(t2,NULL); /*wait for producer */
pthread_join(t1,NULL);/*wait for consumer */
return 0;
}
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