git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@153616 65c4cc65-6c06-0410-ace0-fbb531ad65f3
103 lines
3.7 KiB
C
103 lines
3.7 KiB
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>
|
|
#include <string.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.
|
|
*/
|
|
|
|
static const char explanation[] =
|
|
"This file is created when Asterisk is run with a realtime priority (-p). It\n"
|
|
"must continue to exist, and the astcanary process must be allowed to continue\n"
|
|
"running, or else the Asterisk process will, within a short period of time,\n"
|
|
"slow itself down to regular priority.\n\n"
|
|
"The technical explanation for this file is to provide an assurance to Asterisk\n"
|
|
"that there are no threads that have gone into runaway mode, thus hogging the\n"
|
|
"CPU, and making the Asterisk machine seem to be unresponsive. When that\n"
|
|
"happens, the astcanary process will be unable to update the timestamp on this\n"
|
|
"file, and Asterisk will notice within 120 seconds and react. Slowing the\n"
|
|
"Asterisk process down to regular priority will permit an administrator to\n"
|
|
"intervene, thus avoiding a need to reboot the entire machine.\n";
|
|
|
|
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) {
|
|
if (write(fd, explanation, strlen(explanation)) < 0) {
|
|
exit(1);
|
|
}
|
|
close(fd);
|
|
} else {
|
|
exit(1);
|
|
}
|
|
continue;
|
|
}
|
|
|
|
/* Run occasionally */
|
|
sleep(5);
|
|
}
|
|
|
|
/* Never reached */
|
|
return 0;
|
|
}
|
|
|