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<?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 $threads=1;
const EXIT_OK = 0;
const EXIT_ERR = 1;
const EXIT_SHUTDOWN = 100;
const EXIT_RESTART = 101;
function __construct($id=null, $daemonize=true, $threads=1)
{
parent::__construct($daemonize);
if ($id) {
$this->set_id($id);
}
$this->threads = $threads;
}
/**
* Perform some actual work!
*
* @return int exit code; use self::EXIT_SHUTDOWN to request not to respawn.
*/
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()
{
$this->initPipes();
$children = array();
for ($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;
}
sleep(common_config('queue', 'spawndelay'));
}
$this->log(LOG_INFO, "Waiting for children to complete.");
while (count($children) > 0) {
$status = null;
$pid = pcntl_wait($status);
if ($pid > 0) {
$i = array_search($pid, $children);
if ($i === false) {
$this->log(LOG_ERR, "Ignoring exit of unrecognized child pid $pid");
continue;
}
if (pcntl_wifexited($status)) {
$exitCode = pcntl_wexitstatus($status);
$info = "status $exitCode";
} else if (pcntl_wifsignaled($status)) {
$exitCode = self::EXIT_ERR;
$signal = pcntl_wtermsig($status);
$info = "signal $signal";
}
unset($children[$i]);
if ($this->shouldRespawn($exitCode)) {
$this->log(LOG_INFO, "Thread $i pid $pid exited with $info; 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;
}
sleep(common_config('queue', 'spawndelay'));
} else {
$this->log(LOG_INFO, "Thread $i pid $pid exited with status $exitCode; closing out thread.");
}
}
}
$this->log(LOG_INFO, "All child processes complete.");
return true;
}
/**
* Create an IPC socket pair which child processes can use to detect
* if the parent process has been killed.
*/
function initPipes()
{
$sockets = stream_socket_pair(STREAM_PF_UNIX, STREAM_SOCK_STREAM, 0);
if ($sockets) {
$this->parentWriter = $sockets[0];
$this->parentReader = $sockets[1];
} else {
$this->log(LOG_ERROR, "Couldn't create inter-process sockets");
exit(1);
}
}
/**
* Build an IOManager that simply ensures that we have a connection
* to the parent process open. If it breaks, the child process will
* die.
*
* @return ProcessManager
*/
public function processManager()
{
return new ProcessManager($this->parentReader);
}
/**
* 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 ($exitCode == self::EXIT_SHUTDOWN) {
// Thread requested a clean shutdown.
return false;
} else {
// Otherwise we should always respawn!
return true;
}
}
/**
* Initialize things for a fresh thread, call runThread(), and
* exit at completion with appropriate return value.
*/
protected function initAndRunChild($thread)
{
// Close the writer end of our parent<->children pipe.
fclose($this->parentWriter);
$this->set_id($this->get_id() . "." . $thread);
$this->resetDb();
$exitCode = $this->runThread();
exit($exitCode);
}
/**
* 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());
}
}
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