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<?php
/**
* Class for managing forking command line scripts.
* Currently just does forking and process control, but it could easily be extended
* to provide IPC and job dispatch.
*
* This class requires the posix and pcntl extensions.
*
* @ingroup Maintenance
*/
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,
);
/**
* Pass this flag to __construct() to cause the class to automatically restart
* workers that exit with non-zero exit status or a signal such as SIGSEGV.
*/
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;
}
/**
* Start the child processes.
*
* This should only be called from the command line. It should be called
* as early as possible during execution.
*
* This will return 'child' in the child processes. In the parent process,
* it will run until all the child processes exit or a TERM signal is
* received. It will then return 'done'.
*/
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;
}
/**
* Fork a number of worker processes.
*
* @return string
*/
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;
}
}
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