c - 如果我们在 Unix 中的 pthread_cleanup_push 和 pthread_cleanup_pop 之间返回会发生什么？为什么？

Question

我在Advanced Programming in the UNIX Environment (3rd Edition)中读到了这一点,11.5,线程终止:

If we run the same program on FreeBSD or Mac OS X, we see that the program incurs a segmentation violation and drops core. This happens because on these systems, pthread_cleanup_push is implemented as a macro that stores some context on the stack. When thread 1 returns in between the call to pthread_cleanup_push and the call to pthread_cleanup_pop, the stack is overwritten and these platforms try to use this (now corrupted) context when they invoke the cleanup handlers. In the Single UNIX Specification, returning while in between a matched pair of calls to pthread_cleanup_push and pthread_cleanup_pop results in undefined behavior. The only portable way to return in between these two functions is to call pthread_exit.

那么，我想知道什么是所谓的堆栈上的上下文，以及什么是被覆盖和损坏的上下文，以及为什么 return 不能按预期工作？

Answer 1

当调用 C 函数时，它会在内存的“堆栈”部分存储一些信息(如局部变量)。同样，当这个函数调用另一个函数时，这个新函数将其信息存储在调用函数的信息之后。

当函数调用结束时，它的内存被释放/释放，类似于从堆栈中取出一个盘子。该空间现在可以重复使用。

memory http://www.firmcodes.com/wp-content/uploads/2014/08/memory.png

如果将pthread_cleanup_push实现为在堆栈上存储信息(上下文)的宏，则该内存将被释放，并且可能会被下一个函数调用覆盖。

如果这种情况发生在调用 pthread_cleanup_pop 之前，则“上下文”很可能会被连续的函数调用覆盖，从而破坏 pthread_cleanup_pop 所期望的内存从中读取。