pthread_join使一个线程等待另一个线程结束。

我们知道，如果没有pthread_join主线程会很快结束从而使整个进程结束，从而使创建的线程没有机会开始执行就结束了。加入pthread_join后，主线程会一直等待直到等待的线程结束自己才结束，使创建的线程有机会执行。

1.pthread_join

#include <pthread.h>

int pthread_join(pthread_t thread, void **value_ptr);

参数： - thread：等待退出线程的线程号。 - value_ptr：退出线程的返回值。

返回值： - 成功返回0，失败返回非0。

实例：

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

void *thr_fn(void *arg)
{
    printf("son thread is running...\n");
    sleep(3);
    printf("************son thread will exit************\n");
}

int main(int argc, char const *argv[])
{
    printf("main thread is running....\n");
    pthread_t thread;

    //线程传参
    if (pthread_create(&thread, NULL, thr_fn, NULL) != 0)
    {
        perror("error to pthread_create:");
        exit(-1);
    }

    //等待子线程的结束
    if (pthread_join(thread, NULL) != 0)
    {
        perror("error to join:");
        exit(-1);
    }

    printf("main thread will exit....\n");

    return 0;
}

执行结果：

[root@iz2zefozq9h39txdb8s7npz shelldemo]# ./a.out
main thread is running....
son thread is running...
************son thread will exit************
main thread will exit....

获取子线程的返回值：

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

void *thr_fn(void *arg)
{
    //尽量不要使用栈区的变量，比如int status=666;
    static int status=666;
    printf("son thread is running...\n");

    sleep(3);
    printf("************son thread will exit************\n");
    return (void *)&status;
}

int main(int argc, char const *argv[])
{
    printf("main thread is running....\n");
    pthread_t thread;

    //线程传参
    if (pthread_create(&thread, NULL, thr_fn, NULL) != 0)
    {
        perror("error to pthread_create:");
        exit(-1);
    }

    int *status;

    //等待子线程的结束
    if (pthread_join(thread, (void **)&status) != 0)
    {
        perror("error to join:");
        exit(-1);
    }

    printf("return status=%d\n",*status);
    printf("main thread will exit....\n");

    return 0;
}

运行结果：

[root@iz2zefozq9h39txdb8s7npz shelldemo]# ./a.out
main thread is running....
son thread is running...
************son thread will exit************
return status=666
main thread will exit....