1 files changed, 84 insertions, 0 deletions
diff --git a/trunk/utils/astcanary.c b/trunk/utils/astcanary.c
new file mode 100644
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+++ b/trunk/utils/astcanary.c
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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)) > -1)
+				close(fd);
+			else
+				exit(1);
+			continue;
+		}
+
+		/* Run occasionally */
+		sleep(5);
+	}
+
+	/* Never reached */
+	return 0;
+}
+