The previous attempt at using a pipe to guarantee astcanary shutdown did not work.

We're revisiting the previous patch, albeit with a method that overcomes the
prior criticism that it was not POSIX-compliant.
(closes issue #16602)
 Reported by: frawd
 Patches: 
       20100114__issue16602.diff.txt uploaded by tilghman (license 14)
 Tested by: frawd


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@240499 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/asterisk.c

@@ -276,7 +276,6 @@ static int restartnow;
 static pthread_t consolethread = AST_PTHREADT_NULL;
 static int canary_pid = 0;
 static char canary_filename[128];
-static int canary_pipe = -1;
 
 static char randompool[256];
 
@@ -3495,15 +3494,6 @@ int main(int argc, char *argv[])
 
 	/* Spawning of astcanary must happen AFTER the call to daemon(3) */
 	if (isroot && ast_opt_high_priority) {
-		int cpipe[2];
-
-		/* PIPE signal ensures that astcanary dies when Asterisk dies */
-		if (pipe(cpipe)) {
-			fprintf(stderr, "Unable to open pipe for canary process: %s\n", strerror(errno));
-			exit(1);
-		}
-		canary_pipe = cpipe[0];
-
 		snprintf(canary_filename, sizeof(canary_filename), "%s/alt.asterisk.canary.tweet.tweet.tweet", ast_config_AST_RUN_DIR);
 
 		/* Don't let the canary child kill Asterisk, if it dies immediately */
@@ -3511,18 +3501,17 @@ int main(int argc, char *argv[])
 
 		canary_pid = fork();
 		if (canary_pid == 0) {
-			char canary_binary[128], *lastslash;
+			char canary_binary[128], *lastslash, ppid[12];
 
 			/* Reset signal handler */
 			signal(SIGCHLD, SIG_DFL);
 			signal(SIGPIPE, SIG_DFL);
 
-			dup2(cpipe[1], 0);
-			close(cpipe[1]);
 			ast_close_fds_above_n(0);
 			ast_set_priority(0);
+			snprintf(ppid, sizeof(ppid), "%d", (int) getpid());
 
-			execlp("astcanary", "astcanary", canary_filename, (char *)NULL);
+			execlp("astcanary", "astcanary", canary_filename, ppid, (char *)NULL);
 
 			/* If not found, try the same path as used to execute asterisk */
 			ast_copy_string(canary_binary, argv[0], sizeof(canary_binary));
@@ -3535,12 +3524,11 @@ int main(int argc, char *argv[])
 			_exit(1);
 		} else if (canary_pid > 0) {
 			pthread_t dont_care;
-			close(cpipe[1]);
 			ast_pthread_create_detached(&dont_care, NULL, canary_thread, NULL);
 		}
 
 		/* Kill the canary when we exit */
-		atexit(canary_exit);
+		ast_register_atexit(canary_exit);
 	}
 
 	if (ast_event_init()) {

utils/astcanary.c

@@ -87,9 +87,25 @@ static const char explanation[] =
 int main(int argc, char *argv[])
 {
 	int fd;
+	pid_t parent;
+
+	if (argc < 3) {
+		fprintf(stderr, "Usage: %s <monitor-filename> <ppid>\n", argv[0]);
+		exit(1);
+	}
+
 	/* Run at normal priority */
 	setpriority(PRIO_PROCESS, 0, 0);
-	for (;;) {
+
+	/*!\note
+	 * See http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap03.html#tag_03_265
+	 * for a justification of this approach.  The PPID after the creator dies in Linux and
+	 * most other Unix-like systems will be 1, but this is not strictly the case.  The POSIX
+	 * specification allows it to be an implementation-defined system process.  However, it
+	 * most certainly will not be the original parent PID, which makes the following code
+	 * POSIX-compliant.
+	 */
+	for (parent = atoi(argv[2]); parent == getppid() ;) {
 		/* Update the modification times (checked from Asterisk) */
 		if (utime(argv[1], NULL)) {
 			/* Recreate the file if it doesn't exist */
@@ -108,7 +124,7 @@ int main(int argc, char *argv[])
 		sleep(5);
 	}
 
-	/* Never reached */
+	/* Exit when the parent dies */
 	return 0;
 }