在使用多线程时，需要注意线程之间的同步问题，避免出现数据竞争等情况。同时，应该使用一些工具来检查和调试多线程程序，例如使用线程安全的数据结构、锁和信号量等。

以下是一个代码示例，通过使用锁和条件变量来保证线程同步，避免未执行就退出的问题：

#include 
#include 
#include 

pthread_mutex_t count_lock;
pthread_cond_t count_nonzero;
int count = 0;

void *decrement_count(void *t)
{
    pthread_mutex_lock(&count_lock);
    while (count == 0)
    {
        pthread_cond_wait(&count_nonzero, &count_lock);
    }
    count--;
    printf("Thread %ld: count is %d\n", (long)t, count);
    pthread_mutex_unlock(&count_lock);
    return NULL;
}

void *increment_count(void *t)
{
    pthread_mutex_lock(&count_lock);
    count++;
    printf("Thread %ld: count is %d\n", (long)t, count);
    pthread_cond_signal(&count_nonzero);
    pthread_mutex_unlock(&count_lock);
    return NULL;
}

int main(int argc, char *argv[])
{
    long t;
    pthread_t threads[3];

    pthread_mutex_init(&count_lock, NULL);
    pthread_cond_init(&count_nonzero, NULL);

    for (t = 0; t < 3; t++)
    {
        pthread_create(&threads[t], NULL, increment_count, (void *)t);
    }
    for (t = 0; t < 2; t++)
    {
        pthread_create(&threads[t], NULL, decrement_count, (void *)t);
    }

    /* Wait for all threads to complete */
    for (t = 0; t < 3; t++)
    {
        pthread_join(threads[t], NULL);
    }

    pthread_mutex_destroy(&count_lock);
    pthread_cond_destroy(&count_nonzero);

    return 0;
}

在这个例子中，我们使用了一个计数器