ForkController.php

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<?php
use MediaWiki\MediaWikiServices;

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,
    ];

    const RESTART_ON_ERROR = 1;

    public function __construct( $numProcs, $flags = 0 ) {
        if ( PHP_SAPI != 'cli' ) {
            throw new MWException( "ForkController cannot be used from the web." );
        }
        $this->procsToStart = $numProcs;
        $this->flags = $flags;
    }

    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 ) {
                    $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';
    }

    public function getChildNumber() {
        return $this->childNumber;
    }

    protected function prepareEnvironment() {
        global $wgMemc;
        // Don't share DB, storage, or memcached connections
        MediaWikiServices::resetChildProcessServices();
        FileBackendGroup::destroySingleton();
        LockManagerGroup::destroySingletons();
        JobQueueGroup::destroySingletons();
        ObjectCache::clear();
        RedisConnectionPool::destroySingletons();
        $wgMemc = null;
    }

    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() {
        global $wgMemc, $wgMainCacheType;
        $wgMemc = wfGetCache( $wgMainCacheType );
        $this->children = null;
        pcntl_signal( SIGTERM, SIG_DFL );
    }

    protected function handleTermSignal( $signal ) {
        $this->termReceived = true;
    }
}