我刚开始看线程，大家帮我看看下面的程序有什么问题。在第一个pthread_cond_wait那里就卡住了

#include 
#include 
#include 

pthread_mutex_t mymutex;
pthread_cond_t mycond;

void *thread_function1(void *arg) {
        printf("1st: broad cast myondn");
        pthread_cond_broadcast(&mycond);
        return NULL;
}

void *thread_function2(void *arg) {
        sleep(2);
        printf("2st: broad cast myondn");
        pthread_cond_broadcast(&mycond);
        return NULL;
}

int main(int argc, char **argv) {
        int ret;
        pthread_t mythread1;
        pthread_t mythread2;

        pthread_mutex_init(&mymutex, NULL);
        pthread_cond_init(&mycond, NULL);

        if (pthread_create(&mythread1, NULL, thread_function1, NULL)) {
                printf("create thread1 errorn");
        }

        pthread_mutex_lock(&mymutex);
        pthread_cond_wait(&mycond, &mymutex);
        pthread_mutex_unlock(&mymutex);
        printf("wait1n");

        if (pthread_create(&mythread2, NULL, thread_function2, NULL)) {
                printf("create thread2 errorn");
        }

        pthread_mutex_lock(&mymutex);
        pthread_cond_wait(&mycond, &mymutex);
        pthread_mutex_unlock(&mymutex);
        printf("wait2n");
        return 0;
}

if (pthread_create(&mythread1, NULL, thread_function1, NULL)) {
                printf("create thread1 errorn");
        }
执行之后，thread_function1的pthread_cond_broadcast(&mycond);可能执行比main的pthread_cond_wait(&mycond, &mymutex);还要早，信号丢失了，程序当然就在第一个pthread_cond_wait那里就卡住了

信号量应该配合条件变量使用，应该改成：
#include 
#include 
#include 

pthread_mutex_t mymutex;
pthread_cond_t mycond;
int ret=0,ret2=0;

void *thread_function1(void *arg) {
pthread_mutex_lock(&mymutex);
ret = 1;
        printf("1st: broad cast myondn");
        pthread_cond_broadcast(&mycond);
        pthread_mutex_unlock(&mymutex);
        return NULL;
}

void *thread_function2(void *arg) {
pthread_mutex_lock(&mymutex);
ret2 = 1;
        sleep(2);
        printf("2st: broad cast myondn");
        pthread_cond_broadcast(&mycond);
        pthread_mutex_unlock(&mymutex);
        return NULL;
}

int main(int argc, char **argv) {
        pthread_t mythread1;
        pthread_t mythread2;

        pthread_mutex_init(&mymutex, NULL);
        pthread_cond_init(&mycond, NULL);

        if (pthread_create(&mythread1, NULL, thread_function1, NULL)) {
                printf("create thread1 errorn");
        }

        pthread_mutex_lock(&mymutex);
        if (ret==0)
        {
         pthread_cond_wait(&mycond, &mymutex);
        }
        pthread_mutex_unlock(&mymutex);
        printf("wait1n");

        if (pthread_create(&mythread2, NULL, thread_function2, NULL)) {
                printf("create thread2 errorn");
        }

        pthread_mutex_lock(&mymutex);
        if (ret2==0)
        {
         pthread_cond_wait(&mycond, &mymutex);
}
        pthread_mutex_unlock(&mymutex);
        printf("wait2n");
        return 0;
}

不是应该晚于，而是如果你的信号先broadcast了，然后再wait，你可以wait得到信号吗？