XMPP queued output & initial retooling of DB queue manager to support non-Notice objects.

Queue handlers for XMPP individual & firehose output now send their XML stanzas
to another output queue instead of connecting directly to the chat server. This
lets us have as many general processing threads as we need, while all actual
XMPP input and output go through a single daemon with a single connection open.

This avoids problems with multiple connected resources:
* multiple windows shown in some chat clients (psi, gajim, kopete)
* extra load on server
* incoming message delivery forwarding issues

Database changes:
* queue_item drops 'notice_id' in favor of a 'frame' blob.
  This is based on Craig Andrews' work branch to generalize queues to take any
  object, but conservatively leaving out the serialization for now.
  Table updater (preserves any existing queued items) in db/rc3to09.sql

Code changes to watch out for:
* Queue handlers should now define a handle() method instead of handle_notice()
* QueueDaemon and XmppDaemon now share common i/o (IoMaster) and respawning
  thread management (RespawningDaemon) infrastructure.
* The polling XmppConfirmManager has been dropped, as the message is queued
  directly when saving IM settings.
* Enable $config['queue']['debug_memory'] to output current memory usage at
  each run through the event loop to watch for memory leaks

To do:
* Adapt XMPP i/o to component connection mode for multi-site support.
* XMPP input can also be broken out to a queue, which would allow the actual
  notice save etc to be handled by general queue threads.
* Make sure there are no problems with simply pushing serialized Notice objects
  to queues.
* Find a way to improve interactive performance of the database-backed queue
  handler; polling is pretty painful to XMPP.
* Possibly redo the way QueueHandlers are injected into a QueueManager. The
  grouping used to split out the XMPP output queue is a bit awkward.

1 files changed, 159 insertions, 0 deletions

diff --git a/lib/spawningdaemon.php b/lib/spawningdaemon.php
new file mode 100644
index 000000000..8baefe88e
--- /dev/null
+++ b/lib/spawningdaemon.php
@@ -0,0 +1,159 @@
+<?php
+/*
+ * StatusNet - the distributed open-source microblogging tool
+ * Copyright (C) 2010, StatusNet, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Base class for daemon that can launch one or more processing threads,
+ * respawning them if they exit.
+ *
+ * This is mainly intended for indefinite workloads such as monitoring
+ * a queue or maintaining an IM channel.
+ *
+ * Child classes should implement the 
+ *
+ * We can then pass individual items through the QueueHandler subclasses
+ * they belong to. We additionally can handle queues for multiple sites.
+ *
+ * @package QueueHandler
+ * @author Brion Vibber <brion@status.net>
+ */
+abstract class SpawningDaemon extends Daemon
+{
+    protected $threads=1;
+
+    function __construct($id=null, $daemonize=true, $threads=1)
+    {
+        parent::__construct($daemonize);
+
+        if ($id) {
+            $this->set_id($id);
+        }
+        $this->threads = $threads;
+    }
+
+    /**
+     * Perform some actual work!
+     *
+     * @return boolean true on success, false on failure
+     */
+    public abstract function runThread();
+
+    /**
+     * Spawn one or more background processes and let them start running.
+     * Each individual process will execute whatever's in the runThread()
+     * method, which should be overridden.
+     *
+     * Child processes will be automatically respawned when they exit.
+     *
+     * @todo possibly allow for not respawning on "normal" exits...
+     *       though ParallelizingDaemon is probably better for workloads
+     *       that have forseeable endpoints.
+     */
+    function run()
+    {
+        $children = array();
+        for ($i = 1; $i <= $this->threads; $i++) {
+            $pid = pcntl_fork();
+            if ($pid < 0) {
+                $this->log(LOG_ERROR, "Couldn't fork for thread $i; aborting\n");
+                exit(1);
+            } else if ($pid == 0) {
+                $this->initAndRunChild($i);
+            } else {
+                $this->log(LOG_INFO, "Spawned thread $i as pid $pid");
+                $children[$i] = $pid;
+            }
+        }
+        
+        $this->log(LOG_INFO, "Waiting for children to complete.");
+        while (count($children) > 0) {
+            $status = null;
+            $pid = pcntl_wait($status);
+            if ($pid > 0) {
+                $i = array_search($pid, $children);
+                if ($i === false) {
+                    $this->log(LOG_ERR, "Unrecognized child pid $pid exited!");
+                    continue;
+                }
+                unset($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);
+                } else {
+                    $this->log(LOG_INFO, "Respawned thread $i as pid $pid");
+                    $children[$i] = $pid;
+                }
+            }
+        }
+        $this->log(LOG_INFO, "All child processes complete.");
+        return true;
+    }
+
+    /**
+     * Initialize things for a fresh thread, call runThread(), and
+     * exit at completion with appropriate return value.
+     */
+    protected function initAndRunChild($thread)
+    {
+        $this->set_id($this->get_id() . "." . $thread);
+        $this->resetDb();
+        $ok = $this->runThread();
+        exit($ok ? 0 : 1);
+    }
+
+    /**
+     * Reconnect to the database for each child process,
+     * or they'll get very confused trying to use the
+     * same socket.
+     */
+    protected function resetDb()
+    {
+        // @fixme do we need to explicitly open the db too
+        // or is this implied?
+        global $_DB_DATAOBJECT;
+        unset($_DB_DATAOBJECT['CONNECTIONS']);
+
+        // Reconnect main memcached, or threads will stomp on
+        // each other and corrupt their requests.
+        $cache = common_memcache();
+        if ($cache) {
+            $cache->reconnect();
+        }
+
+        // Also reconnect memcached for status_network table.
+        if (!empty(Status_network::$cache)) {
+            Status_network::$cache->close();
+            Status_network::$cache = null;
+        }
+    }
+
+    function log($level, $msg)
+    {
+        common_log($level, get_class($this) . ' ('. $this->get_id() .'): '.$msg);
+    }
+
+    function name()
+    {
+        return strtolower(get_class($this).'.'.$this->get_id());
+    }
+}
+