为什么用条件变量同步时，发生信号丢失呢？

一个线程自加计数变量，如果被3整除，唤醒另一个等待线程输入该变量。代码如下：

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

pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  cond = PTHREAD_COND_INITIALIZER;
int signaled = 0, count = 0;

void* fun1(void* args) {
    for (;;) {
        pthread_mutex_lock(&lock);
        count++;
        if (count % 3 == 0) {
            pthread_cond_signal(&cond);
            if (count > 1000) {
                signaled = 1;
                pthread_mutex_unlock(&lock);
                break;
            }
        }
        pthread_mutex_unlock(&lock);
    }
}

void* fun2(void* args) {
    pthread_mutex_lock(&lock);
    while (!signaled) {
        pthread_cond_wait(&cond, &lock);
        printf("%d\n", count);
    }
    pthread_mutex_unlock(&lock);
}

int main() {
    pthread_t pthid_1, pthid_2;
    pthread_create(&pthid_1, NULL, fun1, NULL);
    pthread_create(&pthid_2, NULL, fun2, NULL);

    void* result;
    pthread_join(pthid_1, &result);
    pthread_join(pthid_2, &result);

    pthread_cond_destroy(&cond);
    pthread_mutex_destroy(&lock);

    return 0;
}

正确结果应该是：3 6 9..... 这样的。
现在的输出是：734 747 762....