Linux多线程3-1_线程终止

一、exit是危险的
如果进程中的任意一个线程调用了exit，_Exit，_exit，那么整个进程就会终止

二、不终止进程的退出方式
普通的单个线程有一下3中方式退出，这样不会终止进程
（1）从启动例程中返回，返回值是线程的退出码
（2）线程可以被同一进程中的其他线程取消
（3）线程调用pthread_exit(void *rval)函数，rval是退出码

void pthread_exit(void *rval)
rval是个无类型的指针，保存线程的退出码，其他线程可以通过返回码链接这个线程

三、手册
PTHREAD_EXIT(3)            Linux Programmer’s Manual           PTHREAD_EXIT(3)

NAME
       pthread_exit - terminate calling thread

SYNOPSIS
       #include

       void pthread_exit(void *retval);

       Compile and link with -pthread.
        //连接线程库
DESCRIPTION
       The  pthread_exit()  function  terminates the calling thread and returns a value via retval that (if the thread is join-
       able) is available to another thread in the same process that calls pthread_join(3).
        //pthread_exit(void *retval)会导致调用它的线程结束，而且返回一个值保存在retval，其他线程可以通过retval来连接到
        //该线程

       Any clean-up handlers established by pthread_cleanup_push(3) that have not yet been popped, are popped (in  the  reverse
       of  the  order  in  which  they  were pushed) and executed.  If the thread has any thread-specific data, then, after the
       clean-up handlers have been executed, the corresponding destructor functions are called, in an unspecified order.
        //通过pthread_cleanup_push(3)建立的清理函数如果还没有弹出执行，那么pthread_exit(void *retval)会导致该函数弹出执行

       When a thread terminates, process-shared resources (e.g., mutexes, condition variables, semaphores,  and  file  descrip-
       tors) are not released, and functions registered using atexit(3) are not called.
        //当一个线程结束了，共享的进程资源并没有被释放

       After the last thread in a process terminates, the process terminates as by calling exit(3) with an exit status of zero;
       thus, process-shared resources are released and functions registered using atexit(3) are called.


RETURN VALUE
       This function does not return to the caller.
        //这个函数没有返回值
ERRORS
       This function always succeeds.
        //这个函数总是成功

CONFORMING TO
       POSIX.1-2001.

NOTES
       Performing a return from the start function of any thread other than the main thread results  in  an  implicit  call  to
       pthread_exit(), using the function’s return value as the thread’s exit status.

       To  allow  other  threads  to continue execution, the main thread should terminate by calling pthread_exit() rather than
       exit(3).
        //为了让其他线程继续执行，主线程退出的时候应该使用pthread_exit()，而不是exit（）

四、实例
1、几种退出方式
    （1）程序架构

    （2）源代码

/*DATE:            2015-3-25
 *AUTHOR:        WJ
 *DESCRIPTION:    验证几种线程到退出方式
 */

#include "apue.h"

void *thread_fun(void *arg)
{
    //如果传到参数1，那么就采用return方式退出
    if(strcmp("1",(char *)arg)==0)
    {
        printf("new thread return!\n");
        return (void *)1;
    }
    //如果传入参数2，那么就采用pthreade_xit方式退出
    if(strcmp("2",(char *)arg)==0)
    {
        printf("new thread pthread_exit!\n");
        pthread_exit((void *)2);
    }
    //如果传入参数3，那么就采用exit方式退出
    if(strcmp("3",(char *)arg)==0)
    {
        printf("new thread exit!\n");
        exit(3);
    }
}

int main(int argc, char *argv[])
{
    int err;
    pthread_t tid;

    err = pthread_create(&tid, NULL, thread_fun, (void *)argv[1]);
    if(err != 0)
    {
        printf("create new  thread failed\n");
        return 0;
    }

    sleep(1);
    printf("main thread\n");
    return 0;
}

2、证明任意一个线程调用exit函数都会导致进程退出

/*DATE：        2015-3-25
 *AUTHOR：        WJ
 *DESCRIPTION： 创建10 个线程，如果线程的参数和随机数相同，那么线程就采用exit方式退出
 */

#include "apue.h"

int num;

void *thread_fun(void *arg)
{
    printf("I'm new thread: %d\n", (int *)arg);

    //如果线程到参数arg和产生到随机数相同，那么线程就采用exit方式退出
    if(num == (int *)arg)
    {
        printf("new thread %d exit!!!\n", (int *)arg);
        exit(0);
    }
    //否则线程睡眠，让其他线程执行
    sleep(2);

    pthread_exit((void *)0);
}

int main()
{
    int err;
    pthread_t tid;

    //产生随机种子
    srand((unsigned int)time(NULL));
    //产生一个10以内到随机数
    num = rand()%11;

    int i=10;
    //创建10个线程，给每个线程传递参数i
    while(i--)
    {
        err = pthread_create(&tid, NULL, thread_fun, (void *)i);
        if(err != 0)
        {
            printf("create new thread failed\n");
            return 0;
        }
    }
    //睡眠1s，让新线程先运行
    sleep(1);
    return 0;
}