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POSIGTERM to all children processes but not parent
 

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  1. POSIGTERM to all children processes but not parent
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    <p>I have a C program that operates by responding to signals. Some signals cause the parent to fork. This allows other processing while the parent continues to respond to signals.</p> <p>When the parent is sent a SIGTERM, I want the forked children to receive a SIGTERM as well. It isn't critical that the children finish handling the SIGTERM before the parent exits.</p> <p>However, with the below code, the children do not receive a SIGTERM when I call <code>kill(0, SIGTERM)</code> from the parent. From the <a href="http://linux.die.net/man/2/kill" rel="nofollow"><code>kill</code> manpage</a>, it looks like all of the children should get this SIGTERM.</p> <p>I have a signal handler setup for the parent.</p> <pre><code>static volatile sig_atomic_t done = 0; const int handled_signals[] = {SIGINT, SIGTERM, 0}; static void set_flag(int signum) { switch (signum) { /* Intentionally exclude SIGQUIT/SIGABRT/etc. as we want to exit * without cleaning up to help with debugging */ case SIGTERM: case SIGINT: done = 1; break; default: /* Should be unreachable, but just in case */ if (signal(signum, SIG_DFL) != SIG_ERR) { raise(signum); } } } static int setup_handlers() { struct sigaction sa; sigset_t block_all; int i; /* Block all other signals while handling a signal. This is okay as * our handler is very brief */ sigfillset(&amp;block_all); sa.sa_mask = block_all; sa.sa_handler = set_flag; for (i = 0; handled_signals[i] != 0; i++) { if (sigaction(handled_signals[i], &amp;sa, NULL)) { err_log("Unable to set sigaction"); return 1; } } /* Ignore SIGCHLD as we don't keep track of child success */ sa.sa_handler = SIG_IGN; if (sigaction(SIGCHLD, &amp;sa, NULL)) { err_log("Unable to ignore SIGCHLD"); return 1; } return 0; } int main() { int i; sigset_t block_mask, orig_mask; setup_handlers(); /* Block all of our handled signals as we will be using * sigsuspend in the loop below */ sigemptyset(&amp;block_mask); for (i = 0; handled_signals[i] != 0; i++) { sigaddset(&amp;block_mask, handled_signals[i]); } if (sigprocmask(SIG_BLOCK, &amp;block_mask, &amp;orig_mask)) { err_log("Error blocking signals"); } while (!done) { if (sigsuspend(&amp;orig_mask) &amp;&amp; errno != EINTR) { err_log("sigsuspend"); } } /* Kill all children */ if (kill(0, SIGTERM)) { err_log("kill(0, SIGTERM))"); } } </code></pre> <p>After getting a signal that requires a fork, I do the following</p> <pre><code>static int unregister_handlers() { struct sigaction sa; int i; sa.sa_handler = SIG_DFL; for (i = 0; handled_signals[i] != 0; i++) { if (sigaction(handled_signals[i], &amp;sa, NULL)) { err_log("sigaction unregister"); return 1; } } if (sigaction(SIGCHLD, &amp;sa, NULL)) { err_log("sigaction SIGCHLD unregister"); return 1; } return 0; } void do_fork() { switch(fork()) { /* Error */ case -1: err_log("fork"); break; /* Child */ case 0: if (unregister_handlers()) { _exit(1); } do_fork_stuff(); _exit(0); break; /* Parent */ default: break; } } </code></pre> <p>In <code>do_fork_stuff</code>, the child sleeps for 30 seconds. I then call <code>kill(0, SIGTERM)</code> from the parent. The children do not terminate.</p> <p>What's the reason the children aren't getting the SIGTERM?</p>
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    1. USNick Garvey
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