includes/ForkController.php

   1 <?php
   2
   3 /**
   4  * Class for managing forking command line scripts.
   5  * Currently just does forking and process control, but it could easily be extended
   6  * to provide IPC and job dispatch.
   7  *
   8  * This class requires the posix and pcntl extensions.
   9  *
  10  * @ingroup Maintenance
  11  */
  12 class ForkController {
  13         var $children = array();
  14         var $termReceived = false;
  15         var $flags = 0, $procsToStart = 0;
  16
  17         static $restartableSignals = array(
  18                 SIGFPE,
  19                 SIGILL,
  20                 SIGSEGV,
  21                 SIGBUS,
  22                 SIGABRT,
  23                 SIGSYS,
  24                 SIGPIPE,
  25                 SIGXCPU,
  26                 SIGXFSZ,
  27         );
  28
  29         /**
  30          * Pass this flag to __construct() to cause the class to automatically restart
  31          * workers that exit with non-zero exit status or a signal such as SIGSEGV.
  32          */
  33         const RESTART_ON_ERROR = 1;
  34
  35         public function __construct( $numProcs, $flags = 0 ) {
  36                 if ( php_sapi_name() != 'cli' ) {
  37                         throw new MWException( "MultiProcess cannot be used from the web." );
  38                 }
  39                 $this->procsToStart = $numProcs;
  40                 $this->flags = $flags;
  41         }
  42
  43         /**
  44          * Start the child processes.
  45          *
  46          * This should only be called from the command line. It should be called
  47          * as early as possible during execution.
  48          *
  49          * This will return 'child' in the child processes. In the parent process,
  50          * it will run until all the child processes exit or a TERM signal is
  51          * received. It will then return 'done'.
  52          */
  53         public function start() {
  54                 // Trap SIGTERM
  55                 pcntl_signal( SIGTERM, array( $this, 'handleTermSignal' ), false );
  56
  57                 do {
  58                         // Start child processes
  59                         if ( $this->procsToStart ) {
  60                                 if ( $this->forkWorkers( $this->procsToStart ) == 'child' ) {
  61                                         return 'child';
  62                                 }
  63                                 $this->procsToStart = 0;
  64                         }
  65
  66                         // Check child status
  67                         $status = false;
  68                         $deadPid = pcntl_wait( $status );
  69
  70                         if ( $deadPid > 0 ) {
  71                                 // Respond to child process termination
  72                                 unset( $this->children[$deadPid] );
  73                                 if ( $this->flags & self::RESTART_ON_ERROR ) {
  74                                         if ( pcntl_wifsignaled( $status ) ) {
  75                                                 // Restart if the signal was abnormal termination
  76                                                 // Don't restart if it was deliberately killed
  77                                                 $signal = pcntl_wtermsig( $status );
  78                                                 if ( in_array( $signal, self::$restartableSignals ) ) {
  79                                                         echo "Worker exited with signal $signal, restarting\n";
  80                                                         $this->procsToStart++;
  81                                                 }
  82                                         } elseif ( pcntl_wifexited( $status ) ) {
  83                                                 // Restart on non-zero exit status
  84                                                 $exitStatus = pcntl_wexitstatus( $status );
  85                                                 if ( $exitStatus != 0 ) {
  86                                                         echo "Worker exited with status $exitStatus, restarting\n";
  87                                                         $this->procsToStart++;
  88                                                 } else {
  89                                                         echo "Worker exited normally\n";
  90                                                 }
  91                                         }
  92                                 }
  93                                 // Throttle restarts
  94                                 if ( $this->procsToStart ) {
  95                                         usleep( 500000 );
  96                                 }
  97                         }
  98
  99                         // Run signal handlers
 100                         if ( function_exists( 'pcntl_signal_dispatch' ) ) {
 101                                 pcntl_signal_dispatch();
 102                         } else {
 103                                 declare (ticks=1) { $status = $status; }
 104                         }
 105                         // Respond to TERM signal
 106                         if ( $this->termReceived ) {
 107                                 foreach ( $this->children as $childPid => $unused ) {
 108                                         posix_kill( $childPid, SIGTERM );
 109                                 }
 110                                 $this->termReceived = false;
 111                         }
 112                 } while ( count( $this->children ) );
 113                 pcntl_signal( SIGTERM, SIG_DFL );
 114                 return 'done';
 115         }
 116
 117         protected function prepareEnvironment() {
 118                 global $wgCaches, $wgMemc;
 119                 // Don't share DB or memcached connections
 120                 wfGetLBFactory()->destroyInstance();
 121                 $wgCaches = array();
 122                 unset( $wgMemc );
 123         }
 124
 125         /**
 126          * Fork a number of worker processes.
 127          */
 128         protected function forkWorkers( $numProcs ) {
 129                 $this->prepareEnvironment();
 130
 131                 // Create the child processes
 132                 for ( $i = 0; $i < $numProcs; $i++ ) {
 133                         // Do the fork
 134                         $pid = pcntl_fork();
 135                         if ( $pid === -1 || $pid === false ) {
 136                                 echo "Error creating child processes\n";
 137                                 exit( 1 );
 138                         }
 139
 140                         if ( !$pid ) {
 141                                 $this->initChild();
 142                                 return 'child';
 143                         } else {
 144                                 // This is the parent process
 145                                 $this->children[$pid] = true;
 146                         }
 147                 }
 148
 149                 return 'parent';
 150         }
 151
 152         protected function initChild() {
 153                 global $wgMemc, $wgMainCacheType;
 154                 $wgMemc = wfGetCache( $wgMainCacheType );
 155                 $this->children = null;
 156                 pcntl_signal( SIGTERM, SIG_DFL );
 157         }
 158
 159         protected function handleTermSignal( $signal ) {
 160                 $this->termReceived = true;
 161         }
 162 }