线程可以安排他退出时需要调用的函数，这与进程可以用atexit函数安排进程退出时需要调用的函数是类似的。这样的函数称为线程清理处理程序，线程可以建立多个清理处理程序。处理程序记录在栈中，也就是说他们的执行顺序与他们注册的顺序相反。

1.线程退出清理函数

#include <pthread.h>
//将清理函数压栈
/*
参数：
rtn:线程清理函数指针
arg:传给清理函数的参数
*/
void pthread_cleanup_push(void (*rtn)(void *), void *arg);
//将清理函数出栈
/*
参数：
execute:清理函数执行标志位
*/
void pthread_cleanup_pop(int execute);

当线程执行以下动作会自动调用清理函数： - 调用pthread_exit退出线程 - 响应其它线程的取消请求 - 用非零execute调用pthread_cleanup_pop

实例： 线程退出时调用清理函数

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

void mycleanup(void *arg)
{
    printf("clean up arg=%s\n", (char *)arg);
    free((char *)arg);
}

void *thr_fn(void *arg)
{
    char *pt = NULL;
    printf("son thread is running...\n");
    pt =(char*)malloc(100);
    pthread_cleanup_push(mycleanup,(void*)(pt));
    bzero(pt,100);
    strcpy(pt,"memory from malloc..");
    printf("before exit...\n");
    sleep(3);
    pthread_exit(NULL); //线程退出时会自动调用清理函数
    printf("before pop...");
    pthread_cleanup_pop(1); //有push就一定要有pop
}

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

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

    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...
before exit...
clean up arg=memory from malloc..
main thread will exit....

线程取消时执行清理函数

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

void mycleanup(void *arg)
{
    printf("clean up arg=%s\n", (char *)arg);
    free((char *)arg);
}

void *thr_fn(void *arg)
{
    char *pt = NULL;
    printf("son thread is running...\n");
    pt =(char*)malloc(100);
    pthread_cleanup_push(mycleanup,(void*)(pt));
    bzero(pt,100);
    strcpy(pt,"memory from malloc..");
    printf("before exit...\n");
    sleep(10);

    printf("before pop...");
    pthread_cleanup_pop(1); //有push就一定要有pop
    return NULL;
}

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

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

    sleep(5);
    //5秒后取消子线程
    pthread_cancel(thread);

    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...
before exit...
clean up arg=memory from malloc..
main thread will exit....

调用pthread_cleanup_pop时执行清理函数

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

void mycleanup_fn1(void *arg)
{
    printf("clean up fn1 arg=%s\n", (char *)arg);
    free((char *)arg);
}

void mycleanup_fn2(void *arg)
{
    printf("clean up fn2... \n");

}

void *thr_fn(void *arg)
{
    char *pt = NULL;
    printf("son thread is running...\n");
    pt =(char*)malloc(100);
    pthread_cleanup_push(mycleanup_fn1,(void*)(pt));
    pthread_cleanup_push(mycleanup_fn2,NULL);

    bzero(pt,100);
    strcpy(pt,"memory from malloc..");
    printf("before exit...\n");

    sleep(3);  
    //注意：pop必须与push的数量匹配
    printf("before pop...\n");
    pthread_cleanup_pop(1); //有push就一定要有pop
    printf("before pop...\n");
    pthread_cleanup_pop(1); //有push就一定要有pop
    return NULL;
}

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

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

    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...
before exit...
before pop...
clean up fn2... 
before pop...
clean up fn1 arg=memory from malloc..
main thread will exit....