pthread_cond_signal惊群现象

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

pthread_mutex_t count_lock;
pthread_cond_t count_ready;
int count;

void *decrement_count(void *arg)
{
        while(1)
        {
                pthread_mutex_lock(&count_lock);
                printf("decrement:waiting\n");
                /*等待满足条件，期间互斥量仍然可用*/
                //      while (count == 0)
                pthread_cond_wait(&count_ready, &count_lock);
                printf("decrement:count = %d\n",  count);
                if (count == 0)
                {
                        printf("exit count:%d\n",count);
                        exit(1);
                }
                count = 0;
                pthread_mutex_unlock(&count_lock);
        }
        pthread_exit(NULL);
}
void *increment_count(void *arg)
{
        while(1)
        {
                pthread_mutex_lock(&count_lock);
//              printf("increment:running\n");
                count = 1;
                /*通知线程条件已满足*/
//              printf("increment:count = %d\n",  count);
                pthread_cond_signal(&count_ready);
                pthread_mutex_unlock(&count_lock);
        }
        pthread_exit(NULL);
}

int main()
{
        pthread_t tid1,tid2,tid3;
        count=0;
        pthread_mutex_init(&count_lock, NULL);
        pthread_cond_init(&count_ready, NULL);

        pthread_create(&tid1, NULL, decrement_count, NULL);
        sleep(3);
        pthread_create(&tid3, NULL, decrement_count, NULL);
        sleep(3);
        pthread_create(&tid2, NULL, increment_count, NULL);
        /*等待decrement退出*/
        pthread_join(tid2, NULL);
        printf("decrement quit\n");
        pthread_join(tid3, NULL);
        pthread_join(tid1, NULL);
        return 0;
}