includes/ForkController.php

   1 <?php
   2 /**
   3  * Class for managing forking command line scripts.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22 use MediaWiki\MediaWikiServices;
  23
  24 /**
  25  * Class for managing forking command line scripts.
  26  * Currently just does forking and process control, but it could easily be extended
  27  * to provide IPC and job dispatch.
  28  *
  29  * This class requires the posix and pcntl extensions.
  30  *
  31  * @ingroup Maintenance
  32  */
  33 class ForkController {
  34         protected $children = [], $childNumber = 0;
  35         protected $termReceived = false;
  36         protected $flags = 0, $procsToStart = 0;
  37
  38         protected static $restartableSignals = [
  39                 SIGFPE,
  40                 SIGILL,
  41                 SIGSEGV,
  42                 SIGBUS,
  43                 SIGABRT,
  44                 SIGSYS,
  45                 SIGPIPE,
  46                 SIGXCPU,
  47                 SIGXFSZ,
  48         ];
  49
  50         /**
  51          * Pass this flag to __construct() to cause the class to automatically restart
  52          * workers that exit with non-zero exit status or a signal such as SIGSEGV.
  53          */
  54         const RESTART_ON_ERROR = 1;
  55
  56         public function __construct( $numProcs, $flags = 0 ) {
  57                 if ( !wfIsCLI() ) {
  58                         throw new MWException( "ForkController cannot be used from the web." );
  59                 }
  60                 $this->procsToStart = $numProcs;
  61                 $this->flags = $flags;
  62         }
  63
  64         /**
  65          * Start the child processes.
  66          *
  67          * This should only be called from the command line. It should be called
  68          * as early as possible during execution.
  69          *
  70          * This will return 'child' in the child processes. In the parent process,
  71          * it will run until all the child processes exit or a TERM signal is
  72          * received. It will then return 'done'.
  73          * @return string
  74          */
  75         public function start() {
  76                 // Trap SIGTERM
  77                 pcntl_signal( SIGTERM, [ $this, 'handleTermSignal' ], false );
  78
  79                 do {
  80                         // Start child processes
  81                         if ( $this->procsToStart ) {
  82                                 if ( $this->forkWorkers( $this->procsToStart ) == 'child' ) {
  83                                         return 'child';
  84                                 }
  85                                 $this->procsToStart = 0;
  86                         }
  87
  88                         // Check child status
  89                         $status = false;
  90                         $deadPid = pcntl_wait( $status );
  91
  92                         if ( $deadPid > 0 ) {
  93                                 // Respond to child process termination
  94                                 unset( $this->children[$deadPid] );
  95                                 if ( $this->flags & self::RESTART_ON_ERROR ) {
  96                                         if ( pcntl_wifsignaled( $status ) ) {
  97                                                 // Restart if the signal was abnormal termination
  98                                                 // Don't restart if it was deliberately killed
  99                                                 $signal = pcntl_wtermsig( $status );
 100                                                 if ( in_array( $signal, self::$restartableSignals ) ) {
 101                                                         echo "Worker exited with signal $signal, restarting\n";
 102                                                         $this->procsToStart++;
 103                                                 }
 104                                         } elseif ( pcntl_wifexited( $status ) ) {
 105                                                 // Restart on non-zero exit status
 106                                                 $exitStatus = pcntl_wexitstatus( $status );
 107                                                 if ( $exitStatus != 0 ) {
 108                                                         echo "Worker exited with status $exitStatus, restarting\n";
 109                                                         $this->procsToStart++;
 110                                                 } else {
 111                                                         echo "Worker exited normally\n";
 112                                                 }
 113                                         }
 114                                 }
 115                                 // Throttle restarts
 116                                 if ( $this->procsToStart ) {
 117                                         usleep( 500000 );
 118                                 }
 119                         }
 120
 121                         // Run signal handlers
 122                         if ( function_exists( 'pcntl_signal_dispatch' ) ) {
 123                                 pcntl_signal_dispatch();
 124                         } else {
 125                                 declare( ticks = 1 ) {
 126                                         $status = $status;
 127                                 }
 128                         }
 129                         // Respond to TERM signal
 130                         if ( $this->termReceived ) {
 131                                 foreach ( $this->children as $childPid => $unused ) {
 132                                         posix_kill( $childPid, SIGTERM );
 133                                 }
 134                                 $this->termReceived = false;
 135                         }
 136                 } while ( count( $this->children ) );
 137                 pcntl_signal( SIGTERM, SIG_DFL );
 138                 return 'done';
 139         }
 140
 141         /**
 142          * Get the number of the child currently running. Note, this
 143          * is not the pid, but rather which of the total number of children
 144          * we are
 145          * @return int
 146          */
 147         public function getChildNumber() {
 148                 return $this->childNumber;
 149         }
 150
 151         protected function prepareEnvironment() {
 152                 global $wgMemc;
 153                 // Don't share DB, storage, or memcached connections
 154                 MediaWikiServices::resetChildProcessServices();
 155                 FileBackendGroup::destroySingleton();
 156                 LockManagerGroup::destroySingletons();
 157                 JobQueueGroup::destroySingletons();
 158                 ObjectCache::clear();
 159                 RedisConnectionPool::destroySingletons();
 160                 $wgMemc = null;
 161         }
 162
 163         /**
 164          * Fork a number of worker processes.
 165          *
 166          * @param int $numProcs
 167          * @return string
 168          */
 169         protected function forkWorkers( $numProcs ) {
 170                 $this->prepareEnvironment();
 171
 172                 // Create the child processes
 173                 for ( $i = 0; $i < $numProcs; $i++ ) {
 174                         // Do the fork
 175                         $pid = pcntl_fork();
 176                         if ( $pid === -1 || $pid === false ) {
 177                                 echo "Error creating child processes\n";
 178                                 exit( 1 );
 179                         }
 180
 181                         if ( !$pid ) {
 182                                 $this->initChild();
 183                                 $this->childNumber = $i;
 184                                 return 'child';
 185                         } else {
 186                                 // This is the parent process
 187                                 $this->children[$pid] = true;
 188                         }
 189                 }
 190
 191                 return 'parent';
 192         }
 193
 194         protected function initChild() {
 195                 global $wgMemc, $wgMainCacheType;
 196                 $wgMemc = wfGetCache( $wgMainCacheType );
 197                 $this->children = null;
 198                 pcntl_signal( SIGTERM, SIG_DFL );
 199         }
 200
 201         protected function handleTermSignal( $signal ) {
 202                 $this->termReceived = true;
 203         }
 204 }