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