Linux多线程3-5_线程清理操作

一、概念
1、线程可以安排它退出时的清理操作，这与进程的可以用atexit函数安排进程退出时需要调用的函数类似。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，所以这些处理程序执行的顺序与他们注册的顺序相反

pthread_cleanup_push（void （*rtn）（void*）， void *args）//注册处理程序
pthread_cleanup_pop（int excute）//清除处理程序

2、当执行以下操作时调用清理函数，清理函数的参数由args传入
    1）、调用pthread_exit
    2）、响应取消请求
    3）、用非零参数调用pthread_cleanup_pop

3、清理函数的必要性
    也许你会认为线程不需什么清理操作，我可以在退出之前把所有该办的事情办了。但是，你不能确保你的线程永远正常的退出，加入它被取消呢。
    清理操作的优越性就在于，如果线程被取消了，那么清理函数会自动调用，这一点你是办不到的

4、清理函数要注意
    pthread_cleanup_push()  和 pthread_cleanup_pop()是用宏定义继承的，宏定义中包含{}，因此他们两要成对出席那
    
二、手册
PTHREAD_CLEANUP_PUSH(3)    Linux Programmer’s Manual   PTHREAD_CLEANUP_PUSH(3)

NAME
       pthread_cleanup_push, pthread_cleanup_pop - push and pop thread cancellation clean-up handlers
        //注册或者销毁线程取消是的清理函数

SYNOPSIS
       #include
        //包含头文件pthread.h

       void pthread_cleanup_push(void (*routine)(void *),
                                 void *arg);
       void pthread_cleanup_pop(int execute);

       Compile and link with -pthread.
        //编译连接线程库

DESCRIPTION
       These functions manipulate the calling thread’s stack of thread-cancellation clean-up handlers.  A clean-up handler is a
       function that is automatically executed when a thread is canceled (or in various other circumstances  described  below);
       it might, for example, unlock a mutex so that it becomes available to other threads in the process.
        //这两个函数处理线程栈中的取消清理函数。一个清理函数会在线程被取消的时候执行，比如它可能去解锁一个互斥量
        //让它可以在其他线程中被使用

       The  pthread_cleanup_push()  function  pushes  routine  onto the top of the stack of clean-up handlers.  When routine is
       later invoked, it will be given arg as its argument.
        //pthread_cleanup_push()函数会将它的第一个参数指向的函数压入栈的顶端，当栈顶的函数被唤醒的时候，arg就是它的参数

       The pthread_cleanup_pop() function removes the routine at the top of the stack of clean-up handlers, and optionally exe-
       cutes it if execute is non-zero.
        //The pthread_cleanup_pop()函数将栈顶的清理函数从栈中清除，如果The pthread_cleanup_pop()的参数不是0 的话，清理
        //函数在被取出的时候还会执行

       A cancellation clean-up handler is popped from the stack and executed in the following circumstances:
        //一个取消清理操作会在一下的情况弹出并执行

       1. When  a  thread is canceled, all of the stacked clean-up handlers are popped and executed in the reverse of the order
          in which they were pushed onto the stack.
        //当线程被取消的时候，所有的被压入栈的清理函数都将弹出并执行，他们执行的顺序与入栈的顺序相反

       2. When a thread terminates by calling pthread_exit(3), all clean-up handlers are executed as described in the preceding
          point.  (Clean-up handlers are not called if the thread terminates by performing a return from the thread start func-
          tion.)
        //当一个线程用pthread_exit退出，所有的清理函数回像上面描述的一样执行。如果线程用return返回，那么清理函数不会
        //执行

       3. When a thread calls pthread_cleanup_pop() with a non-zero execute argument, the top-most clean-up handler  is  popped
          and executed.
        //如果线程以非零参数调用pthread_cleanup_pop()，栈顶的清理函数就会弹出执行

       POSIX.1  permits  pthread_cleanup_push()  and pthread_cleanup_pop() to be implemented as macros that expand to text con-
       taining '{' and '}', respectively.  For this reason, the caller must ensure that calls to  these  functions  are  paired within  the  same
       function,  and at the same lexical nesting level.  (In other words, a clean-up handler is only established during the execution of a
       specified section of code.)
        //在POSIX中， pthread_cleanup_push()  和 pthread_cleanup_pop()是用宏定义继承的，宏定义中包含{}。因此要确保这两个函数
        //是成对调用的

       Calling longjmp(3) (siglongjmp(3)) produces undefined results if any call has been  made  to  pthread_cleanup_push()  or
       pthread_cleanup_pop()  without  the  matching  call  of  the  pair  since  the  jump  buffer  was  filled  by  setjmp(3)
       (sigsetjmp(3)).  Likewise, calling longjmp(3) (siglongjmp(3)) from inside a clean-up handler produces undefined  results
       unless the jump buffer was also filled by setjmp(3) (sigsetjmp(3)) inside the handler.
        //在清理函数中调用longjmp或者siglongjmp都会产生未知的结果，除非他们和setjmp或者sigsetjmp成对的出现

RETURN VALUE
       These functions do not return a value.
        //这两个函数没有返回值

ERRORS
       There are no errors.
        //没有错误码

CONFORMING TO
       POSIX.1-2001.

NOTES
       On  Linux,  the pthread_cleanup_push() and pthread_cleanup_pop() functions are implemented as macros that expand to text
       containing '{' and '}', respectively.  This means that variables declared within the scope  of  paired  calls  to  these functions will
       only be visible within that scope.
        //在Linux中， pthread_cleanup_push()  and pthread_cleanup_pop()是用宏定义继承的，宏定义中包含{}。因此要确保这两个函数
        //是成对调用的

       POSIX.1  says  that  the  effect  of  using  return,  break,  continue,  or  goto to prematurely leave a block bracketed
       pthread_cleanup_push() and pthread_cleanup_pop() is undefined.  Portable applications should avoid doing this.

四、实例
return返回的线程不会执行清理操作，以非0参数调用pthread_cleanup_pop或者用pthread_exit退出的线程会执行清理操作

/*DATE:            2015-4-1
 *AUTHOR:        WJ
 *DESCRIPTION:    线程清理处理程序
 *    pthread_cleanup_push（void （*rtn）（void*）， void *args）//注册处理程序
 *    pthread_cleanup_pop（int excute）//清除处理程序
 *
 *    这两个函数要成对的出现，否则编译无法通过
 *
 *    当执行以下操作时调用清理函数，清理函数的参数由args传入
 *    1、调用pthread_exit
 *    2、响应取消请求（请你来验证）
 *    3、用非零参数调用pthread_cleanup_pop
 */

#include "apue.h"

void *fisrt_clean(void *arg)
{
    printf("%s fisrt clean\n", arg);
    return(void *)0;
}
void *second_clean(void *arg)
{
    printf("%s second clean\n", arg);
    return(void *)0;
}

void *thread_fun1(void *arg)
{
    printf("new thread 1\n");
    pthread_cleanup_push(fisrt_clean, "thread1");
    pthread_cleanup_push(second_clean, "thread1");

    pthread_cleanup_pop(1);
    pthread_cleanup_pop(0);

    return(void *)1;
}
void *thread_fun2(void *arg)
{
    printf("new thread 2\n");
    pthread_cleanup_push(fisrt_clean, "thread2");
    pthread_cleanup_push(second_clean, "thread2");

    pthread_exit((void *)2);
    pthread_cleanup_pop(0);
    pthread_cleanup_pop(0);

}

int main()
{
    pthread_t tid1, tid2;
    int err;

    err =pthread_create(&tid1, NULL, thread_fun1, NULL);
    if(err != 0)
    {
        printf("create new thread 1failed\n");
        return;
    }
    err =pthread_create(&tid2, NULL, thread_fun2, NULL);
    if(err != 0)
    {
        printf("create new thread 2failed\n");
        return;
    }

    sleep(2);

    return 0 ;
}

练习：当一个线程被取消，清理操作会执行

/*DATE:            2015-4-1
 *AUTHOR:        WJ
 *DESCRIPTION:    线程清理处理程序
 *    pthread_cleanup_push（void （*rtn）（void*）， void *args）//注册处理程序
 *    pthread_cleanup_pop（int excute）//清除处理程序
 *
 *    这两个函数要成对的出现，否则编译无法通过
 *
 *    当执行以下操作时调用清理函数，清理函数的参数由args传入
 *    1、调用pthread_exit
 *    2、响应取消请求
 *    3、用非零参数调用pthread_cleanup_pop
 */

#include "apue.h"

void *fisrt_clean(void *arg)
{
    printf("%s fisrt clean\n", arg);
    return(void *)0;
}
void *second_clean(void *arg)
{
    printf("%s second clean\n", arg);
    return(void *)0;
}

void *thread_fun1(void *arg)
{
    printf("new thread 1 start\n");
    //设置清理函数
    pthread_cleanup_push(fisrt_clean, "thread1");
    pthread_cleanup_push(second_clean, "thread1");

    //休眠2s，程序回到主线程，让主线程执行取消操作
    sleep(2);

    pthread_cleanup_pop(1);
    pthread_cleanup_pop(0);

    printf("new thread 1 over\n");
    return(void *)1;
}
void *thread_fun2(void *arg)
{
    printf("new thread 2 start\n");
    //设置清理函数
    pthread_cleanup_push(fisrt_clean, "thread2");
    pthread_cleanup_push(second_clean, "thread2");

    //休眠2s，程序回到主线程，让主线程执行取消操作
    sleep(2);

    printf("new thread 2 over\n");
    pthread_exit((void *)2);
    pthread_cleanup_pop(0);
    pthread_cleanup_pop(0);

}

int main()
{
    pthread_t tid1, tid2;
    int err;

    printf("main thread start\n");
    //创造新线程
    err =pthread_create(&tid1, NULL, thread_fun1, NULL);
    if(err != 0)
    {
        printf("create new thread 1failed\n");
        return;
    }
    err =pthread_create(&tid2, NULL, thread_fun2, NULL);
    if(err != 0)
    {
        printf("create new thread 2failed\n");
        return;
    }

    //休眠1s，让新线程设置清理函数
    sleep(1);

    //取消新线程
    printf("main thread about to cancel new thread\n");
    err = pthread_cancel(tid1);
    if(err)
        printf("cancel new thread 1 failed\n");
    err = pthread_cancel(tid2);
    if(err)
        printf("cancel new thread 2 failed\n");

    //等待新线程结束
    printf("wait for new thread over\n");
    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    printf("main thread over\n");

    return 0 ;
}