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
  23 /**
  24  * Class for managing forking command line scripts.
  25  * Currently just does forking and process control, but it could easily be extended
  26  * to provide IPC and job dispatch.
  27  *
  28  * This class requires the posix and pcntl extensions.
  29  *
  30  * @ingroup Maintenance
  31  */
  32 class ForkController {
  33         protected $children = array(), $childNumber = 0;
  34         protected $termReceived = false;
  35         protected $flags = 0, $procsToStart = 0;
  36
  37         protected static $restartableSignals = array(
  38                 SIGFPE,
  39                 SIGILL,
  40                 SIGSEGV,
  41                 SIGBUS,
  42                 SIGABRT,
  43                 SIGSYS,
  44                 SIGPIPE,
  45                 SIGXCPU,
  46                 SIGXFSZ,
  47         );
  48
  49         /**
  50          * Pass this flag to __construct() to cause the class to automatically restart
  51          * workers that exit with non-zero exit status or a signal such as SIGSEGV.
  52          */
  53         const RESTART_ON_ERROR = 1;
  54
  55         public function __construct( $numProcs, $flags = 0 ) {
  56                 if ( PHP_SAPI != 'cli' ) {
  57                         throw new MWException( "ForkController cannot be used from the web." );
  58                 }
  59                 $this->procsToStart = $numProcs;
  60                 $this->flags = $flags;
  61         }
  62
  63         /**
  64          * Start the child processes.
  65          *
  66          * This should only be called from the command line. It should be called
  67          * as early as possible during execution.
  68          *
  69          * This will return 'child' in the child processes. In the parent process,
  70          * it will run until all the child processes exit or a TERM signal is
  71          * received. It will then return 'done'.
  72          * @return string
  73          */
  74         public function start() {
  75                 // Trap SIGTERM
  76                 pcntl_signal( SIGTERM, array( $this, 'handleTermSignal' ), false );
  77
  78                 do {
  79                         // Start child processes
  80                         if ( $this->procsToStart ) {
  81                                 if ( $this->forkWorkers( $this->procsToStart ) == 'child' ) {
  82                                         return 'child';
  83                                 }
  84                                 $this->procsToStart = 0;
  85                         }
  86
  87                         // Check child status
  88                         $status = false;
  89                         $deadPid = pcntl_wait( $status );
  90
  91                         if ( $deadPid > 0 ) {
  92                                 // Respond to child process termination
  93                                 unset( $this->children[$deadPid] );
  94                                 if ( $this->flags & self::RESTART_ON_ERROR ) {
  95                                         if ( pcntl_wifsignaled( $status ) ) {
  96                                                 // Restart if the signal was abnormal termination
  97                                                 // Don't restart if it was deliberately killed
  98                                                 $signal = pcntl_wtermsig( $status );
  99                                                 if ( in_array( $signal, self::$restartableSignals ) ) {
 100                                                         echo "Worker exited with signal $signal, restarting\n";
 101                                                         $this->procsToStart++;
 102                                                 }
 103                                         } elseif ( pcntl_wifexited( $status ) ) {
 104                                                 // Restart on non-zero exit status
 105                                                 $exitStatus = pcntl_wexitstatus( $status );
 106                                                 if ( $exitStatus != 0 ) {
 107                                                         echo "Worker exited with status $exitStatus, restarting\n";
 108                                                         $this->procsToStart++;
 109                                                 } else {
 110                                                         echo "Worker exited normally\n";
 111                                                 }
 112                                         }
 113                                 }
 114                                 // Throttle restarts
 115                                 if ( $this->procsToStart ) {
 116                                         usleep( 500000 );
 117                                 }
 118                         }
 119
 120                         // Run signal handlers
 121                         if ( function_exists( 'pcntl_signal_dispatch' ) ) {
 122                                 pcntl_signal_dispatch();
 123                         } else {
 124                                 declare( ticks = 1 ) {
 125                                         $status = $status;
 126                                 }
 127                         }
 128                         // Respond to TERM signal
 129                         if ( $this->termReceived ) {
 130                                 foreach ( $this->children as $childPid => $unused ) {
 131                                         posix_kill( $childPid, SIGTERM );
 132                                 }
 133                                 $this->termReceived = false;
 134                         }
 135                 } while ( count( $this->children ) );
 136                 pcntl_signal( SIGTERM, SIG_DFL );
 137                 return 'done';
 138         }
 139
 140         /**
 141          * Get the number of the child currently running. Note, this
 142          * is not the pid, but rather which of the total number of children
 143          * we are
 144          * @return int
 145          */
 146         public function getChildNumber() {
 147                 return $this->childNumber;
 148         }
 149
 150         protected function prepareEnvironment() {
 151                 global $wgMemc;
 152                 // Don't share DB, storage, or memcached connections
 153                 wfGetLBFactory()->destroyInstance();
 154                 FileBackendGroup::destroySingleton();
 155                 LockManagerGroup::destroySingletons();
 156                 ObjectCache::clear();
 157                 $wgMemc = null;
 158         }
 159
 160         /**
 161          * Fork a number of worker processes.
 162          *
 163          * @return string
 164          */
 165         protected function forkWorkers( $numProcs ) {
 166                 $this->prepareEnvironment();
 167
 168                 // Create the child processes
 169                 for ( $i = 0; $i < $numProcs; $i++ ) {
 170                         // Do the fork
 171                         $pid = pcntl_fork();
 172                         if ( $pid === -1 || $pid === false ) {
 173                                 echo "Error creating child processes\n";
 174                                 exit( 1 );
 175                         }
 176
 177                         if ( !$pid ) {
 178                                 $this->initChild();
 179                                 $this->childNumber = $i;
 180                                 return 'child';
 181                         } else {
 182                                 // This is the parent process
 183                                 $this->children[$pid] = true;
 184                         }
 185                 }
 186
 187                 return 'parent';
 188         }
 189
 190         protected function initChild() {
 191                 global $wgMemc, $wgMainCacheType;
 192                 $wgMemc = wfGetCache( $wgMainCacheType );
 193                 $this->children = null;
 194                 pcntl_signal( SIGTERM, SIG_DFL );
 195         }
 196
 197         protected function handleTermSignal( $signal ) {
 198                 $this->termReceived = true;
 199         }
 200 }