utils/astcanary.c

   1 /*
   2  * Asterisk -- An open source telephony toolkit.
   3  *
   4  * Copyright (C) 2007, Digium, Inc.
   5  *
   6  * Tilghman Lesher <tlesher AT digium DOT com>
   7  *
   8  * See http://www.asterisk.org for more information about
   9  * the Asterisk project. Please do not directly contact
  10  * any of the maintainers of this project for assistance;
  11  * the project provides a web site, mailing lists and IRC
  12  * channels for your use.
  13  *
  14  * This program is free software, distributed under the terms of
  15  * the GNU General Public License Version 2. See the LICENSE file
  16  * at the top of the source tree.
  17  */
  18
  19 #include <sys/types.h>
  20 #include <sys/stat.h>
  21 #include <sys/time.h>
  22 #include <sys/resource.h>
  23 #include <utime.h>
  24 #include <fcntl.h>
  25 #include <unistd.h>
  26 #include <stdlib.h>
  27
  28 /*!\brief
  29  * At one time, canaries were carried along with coal miners down
  30  * into a mine.  Their purpose was to alert the miners when they
  31  * had drilled into a pocket of methane gas or another noxious
  32  * substance.  The canary, being the most sensitive animal would
  33  * immediately fall over.  Seeing this, the miners could take
  34  * action to escape the mine, seeing an imminent danger.
  35  *
  36  * This process serves a similar purpose, though with the realtime
  37  * priority being the reason.  When a thread starts running away
  38  * with the processor, it is typically difficult to tell what
  39  * thread caused the problem, as the machine acts as if it is
  40  * locked up (in fact, what has happened is that Asterisk runs at
  41  * a higher priority than even the login shell, so the runaway
  42  * thread hogs all available CPU time.
  43  *
  44  * If that happens, this canary process will cease to get any
  45  * process time, which we can monitor with a realtime thread in
  46  * Asterisk.  Should that happen, that monitoring thread may take
  47  * immediate action to slow down Asterisk to regular priority,
  48  * thus allowing an administrator to login to the system and
  49  * restart Asterisk or perhaps take another course of action
  50  * (such as retrieving a backtrace to let the developers know
  51  * what precisely went wrong).
  52  *
  53  * Note that according to POSIX.1, all threads inside a single
  54  * process must share the same priority, so when the monitoring
  55  * thread deprioritizes itself, it deprioritizes all threads at
  56  * the same time.  This is also why this canary must exist as a
  57  * completely separate process and not simply as a thread within
  58  * Asterisk itself.
  59  */
  60
  61 int main(int argc, char *argv[])
  62 {
  63         int fd;
  64         /* Run at normal priority */
  65         setpriority(PRIO_PROCESS, 0, 0);
  66         for (;;) {
  67                 /* Update the modification times (checked from Asterisk) */
  68                 if (utime(argv[1], NULL)) {
  69                         /* Recreate the file if it doesn't exist */
  70                         if ((fd = open(argv[1], O_RDWR | O_TRUNC | O_CREAT, 0777)) > -1)
  71                                 close(fd);
  72                         else
  73                                 exit(1);
  74                         continue;
  75                 }
  76
  77                 /* Run occasionally */
  78                 sleep(5);
  79         }
  80
  81         /* Never reached */
  82         return 0;
  83 }
  84