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 class ForkController {
  11         var $children = array();
  12         var $termReceived = false;
  13         var $flags = 0, $procsToStart = 0;
  14
  15         static $restartableSignals = array(
  16                 SIGFPE,
  17                 SIGILL,
  18                 SIGSEGV,
  19                 SIGBUS,
  20                 SIGABRT,
  21                 SIGSYS,
  22                 SIGPIPE,
  23                 SIGXCPU,
  24                 SIGXFSZ,
  25         );
  26
  27         /**
  28          * Pass this flag to __construct() to cause the class to automatically restart
  29          * workers that exit with non-zero exit status or a signal such as SIGSEGV.
  30          */
  31         const RESTART_ON_ERROR = 1;
  32
  33         public function __construct( $numProcs, $flags = 0 ) {
  34                 if ( php_sapi_name() != 'cli' ) {
  35                         throw new MWException( "MultiProcess cannot be used from the web." );
  36                 }
  37                 $this->procsToStart = $numProcs;
  38                 $this->flags = $flags;
  39         }
  40
  41         /**
  42          * Start the child processes.
  43          *
  44          * This should only be called from the command line. It should be called
  45          * as early as possible during execution.
  46          *
  47          * This will return 'child' in the child processes. In the parent process,
  48          * it will run until all the child processes exit or a TERM signal is
  49          * received. It will then return 'done'.
  50          */
  51         public function start() {
  52                 // Trap SIGTERM
  53                 pcntl_signal( SIGTERM, array( $this, 'handleTermSignal' ), false );
  54
  55                 do {
  56                         // Start child processes
  57                         if ( $this->procsToStart ) {
  58                                 if ( $this->forkWorkers( $this->procsToStart ) == 'child' ) {
  59                                         return 'child';
  60                                 }
  61                                 $this->procsToStart = 0;
  62                         }
  63
  64                         // Check child status
  65                         $status = false;
  66                         $deadPid = pcntl_wait( $status );
  67
  68                         if ( $deadPid > 0 ) {
  69                                 // Respond to child process termination
  70                                 unset( $this->children[$deadPid] );
  71                                 if ( $this->flags & self::RESTART_ON_ERROR ) {
  72                                         if ( pcntl_wifsignaled( $status ) ) {
  73                                                 // Restart if the signal was abnormal termination
  74                                                 // Don't restart if it was deliberately killed
  75                                                 $signal = pcntl_wtermsig( $status );
  76                                                 if ( in_array( $signal, self::$restartableSignals ) ) {
  77                                                         echo "Worker exited with signal $signal, restarting\n";
  78                                                         $this->procsToStart++;
  79                                                 }
  80                                         } elseif ( pcntl_wifexited( $status ) ) {
  81                                                 // Restart on non-zero exit status
  82                                                 $exitStatus = pcntl_wexitstatus( $status );
  83                                                 if ( $exitStatus != 0 ) {
  84                                                         echo "Worker exited with status $exitStatus, restarting\n";
  85                                                         $this->procsToStart++;
  86                                                 } else {
  87                                                         echo "Worker exited normally\n";
  88                                                 }
  89                                         }
  90                                 }
  91                                 // Throttle restarts
  92                                 if ( $this->procsToStart ) {
  93                                         usleep( 500000 );
  94                                 }
  95                         }
  96
  97                         // Run signal handlers
  98                         if ( function_exists( 'pcntl_signal_dispatch' ) ) {
  99                                 pcntl_signal_dispatch();
 100                         } else {
 101                                 declare (ticks=1) { $status = $status; }
 102                         }
 103                         // Respond to TERM signal
 104                         if ( $this->termReceived ) {
 105                                 foreach ( $this->children as $childPid => $unused ) {
 106                                         posix_kill( $childPid, SIGTERM );
 107                                 }
 108                                 $this->termReceived = false;
 109                         }
 110                 } while ( count( $this->children ) );
 111                 pcntl_signal( SIGTERM, SIG_DFL );
 112                 return 'done';
 113         }
 114
 115         protected function prepareEnvironment() {
 116                 global $wgCaches, $wgMemc;
 117                 // Don't share DB or memcached connections
 118                 wfGetLBFactory()->destroyInstance();
 119                 $wgCaches = array();
 120                 unset( $wgMemc );
 121         }
 122
 123         /**
 124          * Fork a number of worker processes.
 125          */
 126         protected function forkWorkers( $numProcs ) {
 127                 global $wgMemc, $wgCaches, $wgMainCacheType;
 128
 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 }