线程同步（条件变量）

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

pthread_mutex_t mutex;
pthread_cond_t cond;
int x;

void consumer(void)
{
while(1)
{
pthread_mutex_lock(&mutex);
int i;

while(x<3)
{
pthread_cond_wait(&cond,&mutex);
printf("start consumingn",x);
}

while(x>0)
{
x--;
printf("consuming x=%dn",x);
sleep(1);
}

pthread_mutex_unlock(&mutex);
}

pthread_exit(NULL);

}

void producer(void)
{
while(1)
{
pthread_mutex_lock(&mutex);
int i;

for(i=0;i<3-x;i++)
{
x++;
printf("produing x=%dn",x);
sleep(1);
}

if(x>=3)
{
pthread_cond_signal(&cond);
printf("producing completedn",x);
}

pthread_mutex_unlock(&mutex);
sleep(1);
}

pthread_exit(NULL);

}

int main(void)
{
pthread_t id1,id2;
int ret;

ret = pthread_mutex_init(&mutex,NULL);
if(ret!=0)
{
printf("pthread_mutex_init errorn");
exit(1);
}

ret = pthread_cond_init(&cond,NULL);
if(ret!=0)
{
printf("pthread_cond_init errorn");
exit(1);
}

ret = pthread_create(&id1,NULL,(void *)&producer,NULL);
if(ret!=0)
{
printf("pthread_create producer errorn");
exit(1);
}

ret = pthread_create(&id2,NULL,(void *)&consumer,NULL);
if(ret!=0)
{
printf("pthread_create consumer errorn");
exit(1);
}

pthread_join(id1,NULL);
pthread_join(id2,NULL);
return 0;
}