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<?php
/**
* Class for managing forking command line scripts.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
*/
use MediaWiki\MediaWikiServices;
/**
* Class for managing forking command line scripts.
* Currently just does forking and process control, but it could easily be extended
* to provide IPC and job dispatch.
*
* This class requires the posix and pcntl extensions.
*
* @ingroup Maintenance
*/
class ForkController {
protected $children = [], $childNumber = 0;
protected $termReceived = false;
protected $flags = 0, $procsToStart = 0;
protected static $restartableSignals = [
SIGFPE,
SIGILL,
SIGSEGV,
SIGBUS,
SIGABRT,
SIGSYS,
SIGPIPE,
SIGXCPU,
SIGXFSZ,
];
/**
* Pass this flag to __construct() to cause the class to automatically restart
* workers that exit with non-zero exit status or a signal such as SIGSEGV.
*/
private const RESTART_ON_ERROR = 1;
public function __construct( $numProcs, $flags = 0 ) {
if ( !wfIsCLI() ) {
throw new MWException( "ForkController cannot be used from the web." );
}
$this->procsToStart = $numProcs;
$this->flags = $flags;
}
/**
* Start the child processes.
*
* This should only be called from the command line. It should be called
* as early as possible during execution.
*
* This will return 'child' in the child processes. In the parent process,
* it will run until all the child processes exit or a TERM signal is
* received. It will then return 'done'.
* @return string
*/
public function start() {
// Trap SIGTERM
pcntl_signal( SIGTERM, [ $this, 'handleTermSignal' ], false );
do {
// Start child processes
if ( $this->procsToStart ) {
if ( $this->forkWorkers( $this->procsToStart ) == 'child' ) {
return 'child';
}
$this->procsToStart = 0;
}
// Check child status
$status = false;
$deadPid = pcntl_wait( $status );
if ( $deadPid > 0 ) {
// Respond to child process termination
unset( $this->children[$deadPid] );
if ( $this->flags & self::RESTART_ON_ERROR ) {
if ( pcntl_wifsignaled( $status ) ) {
// Restart if the signal was abnormal termination
// Don't restart if it was deliberately killed
$signal = pcntl_wtermsig( $status );
if ( in_array( $signal, self::$restartableSignals ) ) {
echo "Worker exited with signal $signal, restarting\n";
$this->procsToStart++;
}
} elseif ( pcntl_wifexited( $status ) ) {
// Restart on non-zero exit status
$exitStatus = pcntl_wexitstatus( $status );
if ( $exitStatus != 0 ) {
echo "Worker exited with status $exitStatus, restarting\n";
$this->procsToStart++;
} else {
echo "Worker exited normally\n";
}
}
}
// Throttle restarts
if ( $this->procsToStart ) {
usleep( 500000 );
}
}
// Run signal handlers
if ( function_exists( 'pcntl_signal_dispatch' ) ) {
pcntl_signal_dispatch();
} else {
declare( ticks = 1 ) {
// @phan-suppress-next-line PhanPluginDuplicateExpressionAssignment
$status = $status;
}
}
// Respond to TERM signal
if ( $this->termReceived ) {
foreach ( $this->children as $childPid => $unused ) {
posix_kill( $childPid, SIGTERM );
}
$this->termReceived = false;
}
} while ( count( $this->children ) );
pcntl_signal( SIGTERM, SIG_DFL );
return 'done';
}
/**
* Get the number of the child currently running. Note, this
* is not the pid, but rather which of the total number of children
* we are
* @return int
*/
public function getChildNumber() {
return $this->childNumber;
}
protected function prepareEnvironment() {
// Don't share DB, storage, or memcached connections
MediaWikiServices::resetChildProcessServices();
JobQueueGroup::destroySingletons();
ObjectCache::clear();
RedisConnectionPool::destroySingletons();
}
/**
* Fork a number of worker processes.
*
* @param int $numProcs
* @return string
*/
protected function forkWorkers( $numProcs ) {
$this->prepareEnvironment();
// Create the child processes
for ( $i = 0; $i < $numProcs; $i++ ) {
// Do the fork
$pid = pcntl_fork();
if ( $pid === -1 || $pid === false ) {
echo "Error creating child processes\n";
exit( 1 );
}
if ( !$pid ) {
$this->initChild();
$this->childNumber = $i;
return 'child';
} else {
// This is the parent process
$this->children[$pid] = true;
}
}
return 'parent';
}
protected function initChild() {
$this->children = null;
pcntl_signal( SIGTERM, SIG_DFL );
}
protected function handleTermSignal( $signal ) {
$this->termReceived = true;
}
}
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