view rust/chg/src/sighandlers.c @ 44295:142d2a4cb69a

help: add a mechanism to change flags' help depending on config

It seems reasonable to have a similar mechanism for the rest of the
help, but no such thing is implemented.

The goal is to make the help of commands clearer in the presence of
significant default changes, like tweakdefaults or with company-wide
hgrcs. In these cases, a user looking at the help of a command doesn't
exactly know what his hgrc is doing.

Apply to this to the --git option of commands that display diffs, as
this option in particular causes confusion for some reason.

Differential Revision: https://phab.mercurial-scm.org/D8100

/*
 * Signal handlers for cHg
 *
 * Copyright 2011, 2018 Yuya Nishihara <[e-mail]>
 *
 * This software may be used and distributed according to the terms of the
 * GNU General Public License version 2 or any later version.
 */

#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <unistd.h>

static pid_t peerpgid = 0;
static pid_t peerpid = 0;

static void forwardsignal(int sig)
{
	assert(peerpid > 0);
	(void)kill(peerpid, sig);
}

static void forwardsignaltogroup(int sig)
{
	/* prefer kill(-pgid, sig), fallback to pid if pgid is invalid */
	pid_t killpid = peerpgid > 1 ? -peerpgid : peerpid;
	(void)kill(killpid, sig);
}

static void handlestopsignal(int sig)
{
	sigset_t unblockset, oldset;
	struct sigaction sa, oldsa;
	if (sigemptyset(&unblockset) < 0) {
		return;
	}
	if (sigaddset(&unblockset, sig) < 0) {
		return;
	}
	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = SIG_DFL;
	sa.sa_flags = SA_RESTART;
	if (sigemptyset(&sa.sa_mask) < 0) {
		return;
	}

	forwardsignal(sig);
	if (raise(sig) < 0) { /* resend to self */
		return;
	}
	if (sigaction(sig, &sa, &oldsa) < 0) {
		return;
	}
	if (sigprocmask(SIG_UNBLOCK, &unblockset, &oldset) < 0) {
		return;
	}
	/* resent signal will be handled before sigprocmask() returns */
	if (sigprocmask(SIG_SETMASK, &oldset, NULL) < 0) {
		return;
	}
	if (sigaction(sig, &oldsa, NULL) < 0) {
		return;
	}
}

/*
 * Installs signal handlers.
 *
 * Returns 0 on success, -1 on error and errno is set appropriately.
 * Installed handlers wouldn't be cleaned up on error.
 */
int setupsignalhandler(pid_t pid, pid_t pgid)
{
	if (pid <= 0) {
		errno = EINVAL;
		return -1;
	}
	peerpid = pid;
	peerpgid = (pgid <= 1 ? 0 : pgid);

	struct sigaction sa;
	memset(&sa, 0, sizeof(sa));

	/* deadly signals meant to be sent to a process group:
	 * - SIGHUP: usually generated by the kernel, when termination of a
	 *   process causes that process group to become orphaned
	 * - SIGINT: usually generated by the terminal */
	sa.sa_handler = forwardsignaltogroup;
	sa.sa_flags = SA_RESTART;
	if (sigemptyset(&sa.sa_mask) < 0) {
		return -1;
	}
	if (sigaction(SIGHUP, &sa, NULL) < 0) {
		return -1;
	}
	if (sigaction(SIGINT, &sa, NULL) < 0) {
		return -1;
	}

	/* terminate frontend by double SIGTERM in case of server freeze */
	sa.sa_handler = forwardsignal;
	sa.sa_flags |= SA_RESETHAND;
	if (sigaction(SIGTERM, &sa, NULL) < 0) {
		return -1;
	}

	/* notify the worker about window resize events */
	sa.sa_flags = SA_RESTART;
	if (sigaction(SIGWINCH, &sa, NULL) < 0) {
		return -1;
	}
	/* forward user-defined signals */
	if (sigaction(SIGUSR1, &sa, NULL) < 0) {
		return -1;
	}
	if (sigaction(SIGUSR2, &sa, NULL) < 0) {
		return -1;
	}
	/* propagate job control requests to worker */
	sa.sa_handler = forwardsignal;
	sa.sa_flags = SA_RESTART;
	if (sigaction(SIGCONT, &sa, NULL) < 0) {
		return -1;
	}
	sa.sa_handler = handlestopsignal;
	sa.sa_flags = SA_RESTART;
	if (sigaction(SIGTSTP, &sa, NULL) < 0) {
		return -1;
	}

	return 0;
}

/*
 * Restores signal handlers to the default, and masks SIGINT.
 *
 * Returns 0 on success, -1 on error and errno is set appropriately.
 */
int restoresignalhandler(void)
{
	struct sigaction sa;
	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = SIG_DFL;
	sa.sa_flags = SA_RESTART;
	if (sigemptyset(&sa.sa_mask) < 0) {
		return -1;
	}

	if (sigaction(SIGHUP, &sa, NULL) < 0) {
		return -1;
	}
	if (sigaction(SIGTERM, &sa, NULL) < 0) {
		return -1;
	}
	if (sigaction(SIGWINCH, &sa, NULL) < 0) {
		return -1;
	}
	if (sigaction(SIGCONT, &sa, NULL) < 0) {
		return -1;
	}
	if (sigaction(SIGTSTP, &sa, NULL) < 0) {
		return -1;
	}

	/* ignore Ctrl+C while shutting down to make pager exits cleanly */
	sa.sa_handler = SIG_IGN;
	if (sigaction(SIGINT, &sa, NULL) < 0) {
		return -1;
	}

	peerpid = 0;
	return 0;
}