asterisk/utils/astcanary.c

/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2007, Digium, Inc.
 *
 * Tilghman Lesher <tlesher AT digium DOT com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <utime.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>

/*!\brief
 * At one time, canaries were carried along with coal miners down
 * into a mine.  Their purpose was to alert the miners when they
 * had drilled into a pocket of methane gas or another noxious
 * substance.  The canary, being the most sensitive animal would
 * immediately fall over.  Seeing this, the miners could take
 * action to escape the mine, seeing an imminent danger.
 *
 * This process serves a similar purpose, though with the realtime
 * priority being the reason.  When a thread starts running away
 * with the processor, it is typically difficult to tell what
 * thread caused the problem, as the machine acts as if it is
 * locked up (in fact, what has happened is that Asterisk runs at
 * a higher priority than even the login shell, so the runaway
 * thread hogs all available CPU time.
 *
 * If that happens, this canary process will cease to get any
 * process time, which we can monitor with a realtime thread in
 * Asterisk.  Should that happen, that monitoring thread may take
 * immediate action to slow down Asterisk to regular priority,
 * thus allowing an administrator to login to the system and
 * restart Asterisk or perhaps take another course of action
 * (such as retrieving a backtrace to let the developers know
 * what precisely went wrong).
 *
 * Note that according to POSIX.1, all threads inside a single
 * process must share the same priority, so when the monitoring
 * thread deprioritizes itself, it deprioritizes all threads at
 * the same time.  This is also why this canary must exist as a
 * completely separate process and not simply as a thread within
 * Asterisk itself.
 */

int main(int argc, char *argv[])
{
	int fd;
	/* Run at normal priority */
	setpriority(PRIO_PROCESS, 0, 0);
	for (;;) {
		/* Update the modification times (checked from Asterisk) */
		if (utime(argv[1], NULL)) {
			/* Recreate the file if it doesn't exist */
			if ((fd = open(argv[1], O_RDWR | O_TRUNC | O_CREAT, 0777)) > -1)
				close(fd);
			else
				exit(1);
			continue;
		}

		/* Run occasionally */
		sleep(5);
	}

	/* Never reached */
	return 0;
}