ForkController.php

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<?php

class ForkController {
        var $children = array();
        var $termReceived = false;
        var $flags = 0, $procsToStart = 0;

        static $restartableSignals = array(
                SIGFPE,
                SIGILL,
                SIGSEGV,
                SIGBUS,
                SIGABRT,
                SIGSYS,
                SIGPIPE,
                SIGXCPU,
                SIGXFSZ,
        );

        const RESTART_ON_ERROR = 1;

        public function __construct( $numProcs, $flags = 0 ) {
                if ( php_sapi_name() != '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, array( $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';
        }

        protected function prepareEnvironment() {
                global $wgMemc;
                // Don't share DB or memcached connections
                wfGetLBFactory()->destroyInstance();
                ObjectCache::clear();
                $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();
                                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;
        }
}