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<?php
/**
* Manage locks using a lock daemon server.
*
* Version of LockManager based on using lock daemon servers.
* This is meant for multi-wiki systems that may share files.
* All locks are non-blocking, which avoids deadlocks.
*
* All lock requests for a resource, identified by a hash string, will map
* to one bucket. Each bucket maps to one or several peer servers, each
* running LockServerDaemon.php, listening on a designated TCP port.
* A majority of peers must agree for a lock to be acquired.
*
* @ingroup LockManager
* @since 1.19
*/
class LSLockManager extends LockManager {
/** @var Array Mapping of lock types to the type actually used */
protected $lockTypeMap = array(
self::LOCK_SH => self::LOCK_SH,
self::LOCK_UW => self::LOCK_SH,
self::LOCK_EX => self::LOCK_EX
);
/** @var Array Map of server names to server config */
protected $lockServers; // (server name => server config array)
/** @var Array Map of bucket indexes to peer server lists */
protected $srvsByBucket; // (bucket index => (lsrv1, lsrv2, ...))
/** @var Array Map Server connections (server name => resource) */
protected $conns = array();
protected $connTimeout; // float number of seconds
protected $session = ''; // random SHA-1 string
/**
* Construct a new instance from configuration.
*
* $config paramaters include:
* 'lockServers' : Associative array of server names to configuration.
* Configuration is an associative array that includes:
* 'host' - IP address/hostname
* 'port' - TCP port
* 'authKey' - Secret string the lock server uses
* 'srvsByBucket' : Array of 1-16 consecutive integer keys, starting from 0,
* each having an odd-numbered list of server names (peers) as values.
* 'connTimeout' : Lock server connection attempt timeout. [optional]
*
* @param Array $config
*/
public function __construct( array $config ) {
$this->lockServers = $config['lockServers'];
// Sanitize srvsByBucket config to prevent PHP errors
$this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
$this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
if ( isset( $config['connTimeout'] ) ) {
$this->connTimeout = $config['connTimeout'];
} else {
$this->connTimeout = 3; // use some sane amount
}
$this->session = '';
for ( $i = 0; $i < 5; $i++ ) {
$this->session .= mt_rand( 0, 2147483647 );
}
$this->session = wfBaseConvert( sha1( $this->session ), 16, 36, 31 );
}
protected function doLock( array $paths, $type ) {
$status = Status::newGood();
$pathsToLock = array();
// Get locks that need to be acquired (buckets => locks)...
foreach ( $paths as $path ) {
if ( isset( $this->locksHeld[$path][$type] ) ) {
++$this->locksHeld[$path][$type];
} elseif ( isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
$this->locksHeld[$path][$type] = 1;
} else {
$bucket = $this->getBucketFromKey( $path );
$pathsToLock[$bucket][] = $path;
}
}
$lockedPaths = array(); // files locked in this attempt
// Attempt to acquire these locks...
foreach ( $pathsToLock as $bucket => $paths ) {
// Try to acquire the locks for this bucket
$res = $this->doLockingRequestAll( $bucket, $paths, $type );
if ( $res === 'cantacquire' ) {
// Resources already locked by another process.
// Abort and unlock everything we just locked.
foreach ( $paths as $path ) {
$status->fatal( 'lockmanager-fail-acquirelock', $path );
}
$status->merge( $this->doUnlock( $lockedPaths, $type ) );
return $status;
} elseif ( $res !== true ) {
// Couldn't contact any servers for this bucket.
// Abort and unlock everything we just locked.
foreach ( $paths as $path ) {
$status->fatal( 'lockmanager-fail-acquirelock', $path );
}
$status->merge( $this->doUnlock( $lockedPaths, $type ) );
return $status;
}
// Record these locks as active
foreach ( $paths as $path ) {
$this->locksHeld[$path][$type] = 1; // locked
}
// Keep track of what locks were made in this attempt
$lockedPaths = array_merge( $lockedPaths, $paths );
}
return $status;
}
protected function doUnlock( array $paths, $type ) {
$status = Status::newGood();
foreach ( $paths as $path ) {
if ( !isset( $this->locksHeld[$path] ) ) {
$status->warning( 'lockmanager-notlocked', $path );
} elseif ( !isset( $this->locksHeld[$path][$type] ) ) {
$status->warning( 'lockmanager-notlocked', $path );
} else {
--$this->locksHeld[$path][$type];
if ( $this->locksHeld[$path][$type] <= 0 ) {
unset( $this->locksHeld[$path][$type] );
}
if ( !count( $this->locksHeld[$path] ) ) {
unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
}
}
}
// Reference count the locks held and release locks when zero
if ( !count( $this->locksHeld ) ) {
$status->merge( $this->releaseLocks() );
}
return $status;
}
/**
* Get a connection to a lock server and acquire locks on $paths
*
* @param $lockSrv string
* @param $paths Array
* @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
* @return bool Resources able to be locked
*/
protected function doLockingRequest( $lockSrv, array $paths, $type ) {
if ( $type == self::LOCK_SH ) { // reader locks
$type = 'SH';
} elseif ( $type == self::LOCK_EX ) { // writer locks
$type = 'EX';
} else {
return true; // ok...
}
// Send out the command and get the response...
$keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
$response = $this->sendCommand( $lockSrv, 'ACQUIRE', $type, $keys );
return ( $response === 'ACQUIRED' );
}
/**
* Send a command and get back the response
*
* @param $lockSrv string
* @param $action string
* @param $type string
* @param $values Array
* @return string|false
*/
protected function sendCommand( $lockSrv, $action, $type, $values ) {
$conn = $this->getConnection( $lockSrv );
if ( !$conn ) {
return false; // no connection
}
$authKey = $this->lockServers[$lockSrv]['authKey'];
// Build of the command as a flat string...
$values = implode( '|', $values );
$key = sha1( $this->session . $action . $type . $values . $authKey );
// Send out the command...
if ( fwrite( $conn, "{$this->session}:$key:$action:$type:$values\n" ) === false ) {
return false;
}
// Get the response...
$response = fgets( $conn );
if ( $response === false ) {
return false;
}
return trim( $response );
}
/**
* Attempt to acquire locks with the peers for a bucket
*
* @param $bucket integer
* @param $paths Array List of resource keys to lock
* @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
* @return bool|string One of (true, 'cantacquire', 'srverrors')
*/
protected function doLockingRequestAll( $bucket, array $paths, $type ) {
$yesVotes = 0; // locks made on trustable servers
$votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
$quorum = floor( $votesLeft/2 + 1 ); // simple majority
// Get votes for each peer, in order, until we have enough...
foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) {
// Attempt to acquire the lock on this peer
if ( !$this->doLockingRequest( $lockSrv, $paths, $type ) ) {
return 'cantacquire'; // vetoed; resource locked
}
++$yesVotes; // success for this peer
if ( $yesVotes >= $quorum ) {
return true; // lock obtained
}
--$votesLeft;
$votesNeeded = $quorum - $yesVotes;
if ( $votesNeeded > $votesLeft ) {
// In "trust cache" mode we don't have to meet the quorum
break; // short-circuit
}
}
// At this point, we must not have meet the quorum
return 'srverrors'; // not enough votes to ensure correctness
}
/**
* Get (or reuse) a connection to a lock server
*
* @param $lockSrv string
* @return resource
*/
protected function getConnection( $lockSrv ) {
if ( !isset( $this->conns[$lockSrv] ) ) {
$cfg = $this->lockServers[$lockSrv];
wfSuppressWarnings();
$errno = $errstr = '';
$conn = fsockopen( $cfg['host'], $cfg['port'], $errno, $errstr, $this->connTimeout );
wfRestoreWarnings();
if ( $conn === false ) {
return null;
}
$sec = floor( $this->connTimeout );
$usec = floor( ( $this->connTimeout - floor( $this->connTimeout ) ) * 1e6 );
stream_set_timeout( $conn, $sec, $usec );
$this->conns[$lockSrv] = $conn;
}
return $this->conns[$lockSrv];
}
/**
* Release all locks that this session is holding
*
* @return Status
*/
protected function releaseLocks() {
$status = Status::newGood();
foreach ( $this->conns as $lockSrv => $conn ) {
$response = $this->sendCommand( $lockSrv, 'RELEASE_ALL', '', array() );
if ( $response !== 'RELEASED_ALL' ) {
$status->fatal( 'lockmanager-fail-svr-release', $lockSrv );
}
}
return $status;
}
/**
* Get the bucket for resource path.
* This should avoid throwing any exceptions.
*
* @param $path string
* @return integer
*/
protected function getBucketFromKey( $path ) {
$prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
return intval( base_convert( $prefix, 16, 10 ) ) % count( $this->srvsByBucket );
}
/**
* Make sure remaining locks get cleared for sanity
*/
function __destruct() {
$this->releaseLocks();
foreach ( $this->conns as $conn ) {
fclose( $conn );
}
}
}