pthread_cond_broadcast使用示例

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今天在使用pthread_cond_t时，发现pthread_cond_t使用pthread_cond_broadcast函数唤醒多个条件变量时，使用两个互斥量分别控制时，只能唤醒其中一个变量，最后通过测试发现只能使用一个互斥量去控制。
个人理解：
thread1中使用pthread_mutex_lock(&mutex1);加互斥所，然后在pthread_cond_wait(&cond, &mutex1);这样可以保证这期间没有pthread_cond_broadcast或者pthread_cond_signal操作，从而保证条件不会丢失，当pthread_cond_wait(&cond, &mutex1);
完成操作之后，会自动释放互斥量。
然后thread2中的互斥量也紧接着根据上述方式加入等待对列，当调用pthread_cond_broadcast时会根据加入等待队列中的先后顺序依次唤醒他们。当是还是不明白为什么使用两个互斥量就只能唤醒其中一个呢？有清楚的朋友可以留言。

#include <stdio.h>#include <pthread.h>static pthread_cond_t cond;static pthread_mutex_t mutex1;static pthread_mutex_t mutex2;void *thread1_entry(void *arg){        while(1)        {                pthread_mutex_lock(&mutex1);                printf("cond wait cond1\n");                pthread_cond_wait(&cond, &mutex1);                printf("recv cond1\n");                pthread_mutex_unlock(&mutex1);        }}void *thread2_entry(void *arg){        while(1)        {                pthread_mutex_lock(&mutex1);                printf("cond wait cond2\n");                pthread_cond_wait(&cond, &mutex1);                printf("recv cond2\n");                pthread_mutex_unlock(&mutex1);        }}void *thread3_entry(void *arg){        int ret;        while(1)        {                pthread_mutex_lock(&mutex1);                pthread_mutex_lock(&mutex2);                ret = pthread_cond_broadcast(&cond);                if(ret < 0)                {                        printf("pthread_cond_broadcast error\n");                }                pthread_mutex_unlock(&mutex2);                pthread_mutex_unlock(&mutex1);                sleep(2);        }}int main(void){        int ret =0;        pthread_t tid1, tid2, tid3;        ret = pthread_cond_init(&cond, NULL);        if(ret < 0)        {                printf("pthread_cond_init error\n");        }        ret = pthread_mutex_init(&mutex1, NULL);        if(ret < 0)        {                printf("pthread_mutex_init error\n");        }        ret = pthread_mutex_init(&mutex2,NULL);        if(ret < 0)        {                printf("pthread_mutex_init error\n");        }        ret=  pthread_create(&tid1, NULL, thread1_entry, NULL);        if(ret < 0)        {                printf("pthread_create thread1 error\n");        }        ret = pthread_create(&tid2, NULL, thread2_entry, NULL);        if(ret < 0)        {                printf("pthread_create thread2 error\n");        }        sleep(2);        ret = pthread_create(&tid3, NULL, thread3_entry, NULL);        if(ret < 0)        {                printf("pthread_create thread3 error\n");        }#if 0        pthread_mutex_lock(&mutex1);        pthread_mutex_lock(&mutex2);        ret = pthread_cond_broadcast(&cond);        if(ret < 0)        {                printf("pthread_cond_broadcast error\n");        }        pthread_mutex_unlock(&mutex1);        pthread_mutex_unlock(&mutex2);#endif        while(1)        {                sleep(10000);        }        return 0;}

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