c - pthread_cleanup_push 导致语法错误

Question

我尝试在我的代码中添加一个部分，该部分能够在取消的情况下解锁互斥量。这可能会发生并会导致死锁。因此，我尝试添加 pthread_cleanup_push(cleanup_unlock_mutex, &mutex_ftdi); 但是这一行导致从我添加它的行到代码文件末尾的语法错误。如果我注释代码行，程序将编译而不会出现任何错误。我做错了什么？

void cleanup_unlock_mutex(void *p){
    pthread_mutex_unlock(p);
}

....... }else{
                for(unsigned count=0; count <= number_of_requests; count++){
                    pthread_cleanup_push(cleanup_unlock_mutex, &mutex_ftdi);
                    pthread_mutex_lock(&mutex_ftdi);
                    process_requests(count, numberofthread);
                    pthread_mutex_unlock(&mutex_ftdi);
                }
            } // compiler error: error: expected ‘while’ before ‘}’ token
..........

文件中的所有其他函数都会收到警告:ISO C 禁止嵌套函数 [-pedantic]。

Answer 1

您必须成对调用 pthread_cleanup_push() 和 pthread_cleanup_pop()，并且您的代码片段没有 pthread_cleanup_pop() 调用.

文档位于 http://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_cleanup_pop.html解释原因:

These functions may be implemented as macros. The application shall ensure that they appear as statements, and in pairs within the same lexical scope (that is, the pthread_cleanup_push() macro may be thought to expand to a token list whose first token is '{' with pthread_cleanup_pop() expanding to a token list whose last token is the corresponding '}' ).

为了具体化，一种可能的实现，取自 glibc 的 nptl/sysdeps/pthread/pthread.h:

/* Install a cleanup handler: ROUTINE will be called with arguments ARG
   when the thread is canceled or calls pthread_exit.  ROUTINE will also
   be called with arguments ARG when the matching pthread_cleanup_pop
   is executed with non-zero EXECUTE argument.

   pthread_cleanup_push and pthread_cleanup_pop are macros and must always
   be used in matching pairs at the same nesting level of braces.  */
#  define pthread_cleanup_push(routine, arg) \
  do {                                        \
    __pthread_cleanup_class __clframe (routine, arg)

/* Remove a cleanup handler installed by the matching pthread_cleanup_push.
   If EXECUTE is non-zero, the handler function is called. */
#  define pthread_cleanup_pop(execute) \
    __clframe.__setdoit (execute);                        \
  } while (0)