From 58be61b6417119de1b03ef50e166369c4005e4d1 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Tue, 26 Jan 2010 11:49:49 -0800
Subject: Control channel for queue daemons to request graceful shutdown,
 restart, or update to listen to a newly added or reconfigured site.

  queuectl.php --update -s<site>
  queuectl.php --stop
  queuectl.php --restart

Default control channel is /topic/statusnet-control. For external utilities to send a site update ping direct to the queue server, connect via Stomp and send a message formatted thus:

  update:<nickname>

(Nickname here, *not* server hostname! The rest of the queues will be updated to use nicknames later.)

Note that all currently-connected queue daemons will get these notifications, including both queuedaemon.php and xmppdaemon.php. (XMPP will ignore site update requests for sites that it's not handling.)

Limitations:
* only implemented for stomp queue manager so far
* --update may not yet handle a changed server name properly
* --restart won't reload PHP code files that were already loaded at startup. Still need to stop and restart the daemons from 'outside' when updating code base.
---
 lib/spawningdaemon.php | 58 ++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 44 insertions(+), 14 deletions(-)

(limited to 'lib/spawningdaemon.php')

diff --git a/lib/spawningdaemon.php b/lib/spawningdaemon.php
index 8baefe88e..b1961d688 100644
--- a/lib/spawningdaemon.php
+++ b/lib/spawningdaemon.php
@@ -36,6 +36,11 @@ abstract class SpawningDaemon extends Daemon
 {
     protected $threads=1;
 
+    const EXIT_OK = 0;
+    const EXIT_ERR = 1;
+    const EXIT_SHUTDOWN = 100;
+    const EXIT_RESTART = 101;
+
     function __construct($id=null, $daemonize=true, $threads=1)
     {
         parent::__construct($daemonize);
@@ -49,7 +54,7 @@ abstract class SpawningDaemon extends Daemon
     /**
      * Perform some actual work!
      *
-     * @return boolean true on success, false on failure
+     * @return int exit code; use self::EXIT_SHUTDOWN to request not to respawn.
      */
     public abstract function runThread();
 
@@ -84,23 +89,30 @@ abstract class SpawningDaemon extends Daemon
         while (count($children) > 0) {
             $status = null;
             $pid = pcntl_wait($status);
-            if ($pid > 0) {
+            if ($pid > 0 && pcntl_wifexited($status)) {
+                $exitCode = pcntl_wexitstatus($status);
+
                 $i = array_search($pid, $children);
                 if ($i === false) {
-                    $this->log(LOG_ERR, "Unrecognized child pid $pid exited!");
+                    $this->log(LOG_ERR, "Unrecognized child pid $pid exited with status $exitCode");
                     continue;
                 }
                 unset($children[$i]);
-                $this->log(LOG_INFO, "Thread $i pid $pid exited.");
-                
-                $pid = pcntl_fork();
-                if ($pid < 0) {
-                    $this->log(LOG_ERROR, "Couldn't fork to respawn thread $i; aborting thread.\n");
-                } else if ($pid == 0) {
-                    $this->initAndRunChild($i);
+
+                if ($this->shouldRespawn($exitCode)) {
+                    $this->log(LOG_INFO, "Thread $i pid $pid exited with status $exitCode; respawing.");
+
+                    $pid = pcntl_fork();
+                    if ($pid < 0) {
+                        $this->log(LOG_ERROR, "Couldn't fork to respawn thread $i; aborting thread.\n");
+                    } else if ($pid == 0) {
+                        $this->initAndRunChild($i);
+                    } else {
+                        $this->log(LOG_INFO, "Respawned thread $i as pid $pid");
+                        $children[$i] = $pid;
+                    }
                 } else {
-                    $this->log(LOG_INFO, "Respawned thread $i as pid $pid");
-                    $children[$i] = $pid;
+                    $this->log(LOG_INFO, "Thread $i pid $pid exited with status $exitCode; closing out thread.");
                 }
             }
         }
@@ -108,6 +120,24 @@ abstract class SpawningDaemon extends Daemon
         return true;
     }
 
+    /**
+     * Determine whether to respawn an exited subprocess based on its exit code.
+     * Otherwise we'll respawn all exits by default.
+     *
+     * @param int $exitCode
+     * @return boolean true to respawn
+     */
+    protected function shouldRespawn($exitCode)
+    {
+        if ($exitCode == self::EXIT_SHUTDOWN) {
+            // Thread requested a clean shutdown.
+            return false;
+        } else {
+            // Otherwise we should always respawn!
+            return true;
+        }
+    }
+
     /**
      * Initialize things for a fresh thread, call runThread(), and
      * exit at completion with appropriate return value.
@@ -116,8 +146,8 @@ abstract class SpawningDaemon extends Daemon
     {
         $this->set_id($this->get_id() . "." . $thread);
         $this->resetDb();
-        $ok = $this->runThread();
-        exit($ok ? 0 : 1);
+        $exitCode = $this->runThread();
+        exit($exitCode);
     }
 
     /**
-- 
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