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/*
* 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;
}
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