pthread_cond_signal函数的例子

下面是一个使用pthread_cond_signal函数的例子：

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

#define NUM_THREADS 3

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

int count = 0;

void *thread_func(void *arg) {
    int *id = (int *) arg;
    printf("Thread %d started\n", *id);
    
    pthread_mutex_lock(&mutex);
    while (count < 5) {
        printf("Thread %d waiting\n", *id);
        pthread_cond_wait(&cond, &mutex);
        printf("Thread %d continuing\n", *id);
    }
    pthread_mutex_unlock(&mutex);
    
    printf("Thread %d finished\n", *id);
    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];
    int ids[NUM_THREADS] = {0, 1, 2};
    
    for (int i = 0; i < NUM_THREADS; i++) {
        pthread_create(&threads[i], NULL, thread_func, &ids[i]);
    }
    
    pthread_mutex_lock(&mutex);
    for (int i = 0; i < 5; i++) {
        count++;
        printf("Main thread signalling\n");
        pthread_cond_signal(&cond);
    }
    pthread_mutex_unlock(&mutex);
    
    for (int i = 0; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }
    
    return 0;
}

在该例子中，我们创建了三个线程并在主线程中使用pthread_cond_signal函数通知等待线程继续执行。线程等待条件变量cond，当主线程调用pthread_cond_signal函数时，其中一个线程将从等待中醒来并继续执行。注意，我们在使用条件变量时需要使用互斥锁mutex来保护共享数据。