忽略带有sigaction(2)的SIGCHLD信号的用途是什么?

本文介绍了忽略带有sigaction(2)的SIGCHLD信号的用途是什么?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

事实证明，通过指定要被其父级使用sigaction()忽略的SIGCHLD信号，我们可以防止出现僵尸进程(即其父级不是wait()的父级). .但是，看起来SIGCHLD还是默认情况下会被忽略.怎么运作的?

It turns out that we can prevent appearing of a zombie process (i.e. the one whose parent doesn't wait() for it to _exit()) by specifying SIGCHLD signal to be ignored with sigaction() by its parent. However, it seems like SIGCHLD is ignored by default anyway. How come does this work?

int main (void) { struct sigaction sa; sa.sa_handler = SIG_IGN; //handle signal by ignoring sigemptyset(&sa.sa_mask); sa.sa_flags = 0; if (sigaction(SIGCHLD, &sa, 0) == -1) { perror(0); exit(1); } int pid = fork(); if (pid == 0) { //child process _exit(0); } do_something(); //parent process return 0; }

推荐答案

SIGCHLD的默认行为是丢弃信号，但子进程将保持为僵尸状态，直到父进程调用wait()(或变体)为止. )以获取其终止状态.

The default behavior of SIGCHLD is to discard the signal, but the child process is kept as a zombie until the parent calls wait() (or a variant) to get its termination status.

但是，如果您使用处置SIG_IGN显式调用sigaction()，这将导致它不会将孩子变成僵尸-当孩子退出时，它会立即被收割.参见 stackoverflow/a/7171836/1491895

But if you explicitly call sigaction() with the disposition SIG_IGN, that causes it not to turn the child into a zombie -- when the child exits it is reaped immediately. See stackoverflow/a/7171836/1491895

获得此行为的POSIX方法是通过将sigaction与handler = SIG_DFL和flags包含SA_NOCLDWAIT一起调用.从2.6开始，这是在Linux中.

The POSIX way to get this behavior is by calling sigaction with handler = SIG_DFL and flags containing SA_NOCLDWAIT. This is in Linux since 2.6.