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linux线程中如何控制子线程退出

一.相关接口介绍

1.线程的创建-pthread_create
使用man 3 查询函数使用

int pthread_create(pthread_t *thread, //线程id
                   const pthread_attr_t *attr,  //线程属性，一般为空
                   void *(*start_routine) (void *), //线程处理函数
                   void *arg);//线程参数

2.线程取消接口-pthread_cancel

int pthread_cancel(pthread_t thread);

3.线程取消函数，只是给指定线程发送取消的信号，即使发送成功，也不代表子线程会退出，子线程本身需要设置如下
pthread_setcancelstate–是能线程取消功能
pthread_setcanceltype–设置线程取消类型

 int pthread_setcancelstate(int state, int *oldstate);
 int pthread_setcanceltype(int type, int *oldtype);

state 取值：

 PTHREAD_CANCEL_ENABLE  //收到canael信号，取消当前线程
The  thread  is  cancelable.  This is the default cancelability state in all new threads, including the initial thread.
The thread's cancelability type determines when a cancelable thread will respond to a cancellation request.

 PTHREAD_CANCEL_DISABLE//可以理解为忽略cancel信号
 The thread is not cancelable.  If a cancellation request is received, it is blocked until cancelability is enabled.

type取值：

PTHREAD_CANCEL_DEFERRED  //延迟取消，下一个取消点取消，建立取消点函数pthread_testcancel();  
A cancellation request is deferred until  the  thread  next  calls  a  function  that  is  a  cancellation  point  (see pthreads(7)).  This is the default cancelability type in all new threads, including the initial thread.

PTHREAD_CANCEL_ASYNCHRONOUS//立即取消
The  thread  can  be  canceled  at any time.  (Typically, it will be canceled immediately upon receiving a cancellation request, but the system doesn't guarantee this.)

4.pthread_join --主线程阻塞，等待某个子线程退出

5.pthread_exit --线程退出接口

二. 实例

1.异步线程控制子线程退出

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


pthread_t my_thread;

void *  pthread_fun(void * arg)
{

        //收到cancel信号，取消此线程
        pthread_setcancelstate(PTHREAD_CANCEL_ENABLE,NULL);

        //立即取消此线程
        pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS,NULL);


        int  recvmsg = *(int*)arg;



        while(1)
        {
                printf("this msg %d \n",recvmsg);
                sleep(1);
        }
}


int main(int argc, const char *argv[])
{
        int ret = 0;
        int msg = 888;
        int i = 0;
        void * canel_ret;

        ret = pthread_create(&my_thread,NULL,pthread_fun,&msg);
        if(ret != 0)
        {
                printf("pthread create fail \n");
                return ret;
        }

        for(i=0;i<10;i++)
        {
                printf("main i:%d \n",i);
                if(i == 9)
                {
                        pthread_cancel(my_thread);
                }
                sleep(1);
        }

    //等待指定线程退出回收资源
        pthread_join(my_thread,&canel_ret);
        printf("cancel ret %d \n",(int)canel_ret);


        return 0;
}

测试结果，主线程运行10s 后 退出

2.同步退出方法
主线程发送cancel信号后，子线程不会立即退出，需要运行到取消点，退出，如果线程中没有取消点函数，取消点由我们去设置。
sleep函数其实可以把它当做一个取消点的，或者使用pthread_testcancel自己设置。

注意：被取消的线程，退出值，定义在Linux的pthread库中常数PTHREAD_CANCELED的值是-1。
取消点函数，posix有定义取消点函数。