条件变量例子

#include <stdio.h>
#include <pthread.h>
#define MAXNITEMS 1000000
int nitems;
int buff [MAXNITEMS];

struct
{
	pthread_mutex_t mutex;
	int nput;
	int nval;
}put = {PTHREAD_MUTEX_INITIALIZER};

struct
{
	pthread_mutex_t mutex;
	pthread_cond_t cond;
	int nready;
} nready = {PTHREAD_MUTEX_INITIALIZER,PTHREAD_COND_INITIALIZER};

void *produce(void *arg);
void *consume(void *arg);

int main(int argc, char *argv[])
{
	int i = 0,nthreads = 0,count[5];
	pthread_t tid_produce[5],tid_consume;
	nthreads = 5;
	nitems = MAXNITEMS;
	for(i = 0; i < nthreads; i++)
	{
		count[i] = 0;
		pthread_create(&tid_produce[i], NULL, produce, &count[i]);
	}
	pthread_create(&tid_consume, NULL, consume, NULL);
	
	for(i = 0;i < nthreads; i++ )
	{
		pthread_join(tid_produce[i],NULL);
		printf("count[%d] = %d\n", i, count[i]);
	}
	pthread_join(tid_consume, NULL);


	return 0;
}

void *produce(void *arg)
{
	for( ; ; )
	{
		pthread_mutex_lock(&put.mutex);
		if(put.nput >= nitems)
		{
			pthread_mutex_unlock(&put.mutex);
			return NULL;
		}
		buff[put.nput] = put.nval;
		put.nput++;
		put.nval++;
		pthread_mutex_unlock(&put.mutex);

		pthread_mutex_lock(&nready.mutex);
		if(nready.nready == 0)
		{
			pthread_cond_signal( &nready.cond);
		}
		nready.nready++;
		pthread_mutex_unlock(&nready.mutex);
		*((int *)arg) += 1;
	}
	return NULL;
}

void *consume(void *arg)
{
	int i = 0;
	for(i =0; i < nitems; i++)
	{
		pthread_mutex_lock(&nready.mutex);
		while(nready.nready == 0)
		{
			/*1,阻塞等待条件变量
			  2,解锁unlock
			  3，当某个线程调用pthread_cond_signal时 重新上锁lock
			*/
			pthread_cond_wait(&nready.cond, &nready.mutex);
		}
		nready.nready--;
		pthread_mutex_unlock(&nready.mutex);
		if(buff[i] != i)
		{
			printf("buff[%d] = %d\n", i, buff[i]);
		}
	}
	return NULL;
}