includes/filerepo/backend/lockmanager/LSLockManager.php

   1 <?php
   2
   3 /**
   4  * Version of LockManager based on using lock daemon servers.
   5  * This is meant for multi-wiki systems that may share files.
   6  * All locks are non-blocking, which avoids deadlocks.
   7  *
   8  * All lock requests for a resource, identified by a hash string, will map
   9  * to one bucket. Each bucket maps to one or several peer servers, each
  10  * running LockServerDaemon.php, listening on a designated TCP port.
  11  * A majority of peers must agree for a lock to be acquired.
  12  *
  13  * @ingroup LockManager
  14  */
  15 class LSLockManager extends LockManager {
  16         /** @var Array Mapping of lock types to the type actually used */
  17         protected $lockTypeMap = array(
  18                 self::LOCK_SH => self::LOCK_SH,
  19                 self::LOCK_UW => self::LOCK_SH,
  20                 self::LOCK_EX => self::LOCK_EX
  21         );
  22
  23         /** @var Array Map of server names to server config */
  24         protected $lockServers; // (server name => server config array)
  25         /** @var Array Map of bucket indexes to peer server lists */
  26         protected $srvsByBucket; // (bucket index => (lsrv1, lsrv2, ...))
  27
  28         /** @var Array Map Server connections (server name => resource) */
  29         protected $conns = array();
  30
  31         protected $connTimeout; // float number of seconds
  32         protected $session = ''; // random SHA-1 string
  33
  34         /**
  35          * Construct a new instance from configuration.
  36          *
  37          * $config paramaters include:
  38          *     'lockServers'  : Associative array of server names to configuration.
  39          *                      Configuration is an associative array that includes:
  40          *                      'host'    - IP address/hostname
  41          *                      'port'    - TCP port
  42          *                      'authKey' - Secret string the lock server uses
  43          *     'srvsByBucket' : Array of 1-16 consecutive integer keys, starting from 0,
  44          *                      each having an odd-numbered list of server names (peers) as values.
  45          *     'connTimeout'  : Lock server connection attempt timeout. [optional]
  46          *
  47          * @param Array $config
  48          */
  49         public function __construct( array $config ) {
  50                 $this->lockServers = $config['lockServers'];
  51                 // Sanitize srvsByBucket config to prevent PHP errors
  52                 $this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
  53                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  54
  55                 if ( isset( $config['connTimeout'] ) ) {
  56                         $this->connTimeout = $config['connTimeout'];
  57                 } else {
  58                         $this->connTimeout = 3; // use some sane amount
  59                 }
  60
  61                 $this->session = '';
  62                 for ( $i = 0; $i < 5; $i++ ) {
  63                         $this->session .= mt_rand( 0, 2147483647 );
  64                 }
  65                 $this->session = wfBaseConvert( sha1( $this->session ), 16, 36, 31 );
  66         }
  67
  68         protected function doLock( array $paths, $type ) {
  69                 $status = Status::newGood();
  70
  71                 $pathsToLock = array();
  72                 // Get locks that need to be acquired (buckets => locks)...
  73                 foreach ( $paths as $path ) {
  74                         if ( isset( $this->locksHeld[$path][$type] ) ) {
  75                                 ++$this->locksHeld[$path][$type];
  76                         } elseif ( isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
  77                                 $this->locksHeld[$path][$type] = 1;
  78                         } else {
  79                                 $bucket = $this->getBucketFromKey( $path );
  80                                 $pathsToLock[$bucket][] = $path;
  81                         }
  82                 }
  83
  84                 $lockedPaths = array(); // files locked in this attempt
  85                 // Attempt to acquire these locks...
  86                 foreach ( $pathsToLock as $bucket => $paths ) {
  87                         // Try to acquire the locks for this bucket
  88                         $res = $this->doLockingRequestAll( $bucket, $paths, $type );
  89                         if ( $res === 'cantacquire' ) {
  90                                 // Resources already locked by another process.
  91                                 // Abort and unlock everything we just locked.
  92                                 foreach ( $paths as $path ) {
  93                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
  94                                 }
  95                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
  96                                 return $status;
  97                         } elseif ( $res !== true ) {
  98                                 // Couldn't contact any servers for this bucket.
  99                                 // Abort and unlock everything we just locked.
 100                                 foreach ( $paths as $path ) {
 101                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 102                                 }
 103                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
 104                                 return $status;
 105                         }
 106                         // Record these locks as active
 107                         foreach ( $paths as $path ) {
 108                                 $this->locksHeld[$path][$type] = 1; // locked
 109                         }
 110                         // Keep track of what locks were made in this attempt
 111                         $lockedPaths = array_merge( $lockedPaths, $paths );
 112                 }
 113
 114                 return $status;
 115         }
 116
 117         protected function doUnlock( array $paths, $type ) {
 118                 $status = Status::newGood();
 119
 120                 foreach ( $paths as $path ) {
 121                         if ( !isset( $this->locksHeld[$path] ) ) {
 122                                 $status->warning( 'lockmanager-notlocked', $path );
 123                         } elseif ( !isset( $this->locksHeld[$path][$type] ) ) {
 124                                 $status->warning( 'lockmanager-notlocked', $path );
 125                         } else {
 126                                 --$this->locksHeld[$path][$type];
 127                                 if ( $this->locksHeld[$path][$type] <= 0 ) {
 128                                         unset( $this->locksHeld[$path][$type] );
 129                                 }
 130                                 if ( !count( $this->locksHeld[$path] ) ) {
 131                                         unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
 132                                 }
 133                         }
 134                 }
 135
 136                 // Reference count the locks held and release locks when zero
 137                 if ( !count( $this->locksHeld ) ) {
 138                         $status->merge( $this->releaseLocks() );
 139                 }
 140
 141                 return $status;
 142         }
 143
 144         /**
 145          * Get a connection to a lock server and acquire locks on $paths
 146          *
 147          * @param $lockSrv string
 148          * @param $paths Array
 149          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 150          * @return bool Resources able to be locked
 151          */
 152         protected function doLockingRequest( $lockSrv, array $paths, $type ) {
 153                 if ( $type == self::LOCK_SH ) { // reader locks
 154                         $type = 'SH';
 155                 } elseif ( $type == self::LOCK_EX ) { // writer locks
 156                         $type = 'EX';
 157                 } else {
 158                         return true; // ok...
 159                 }
 160
 161                 // Send out the command and get the response...
 162                 $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 163                 $response = $this->sendCommand( $lockSrv, 'ACQUIRE', $type, $keys );
 164
 165                 return ( $response === 'ACQUIRED' );
 166         }
 167
 168         /**
 169          * Send a command and get back the response
 170          *
 171          * @param $lockSrv string
 172          * @param $action string
 173          * @param $type string
 174          * @param $values Array
 175          * @return string|false
 176          */
 177         protected function sendCommand( $lockSrv, $action, $type, $values ) {
 178                 $conn = $this->getConnection( $lockSrv );
 179                 if ( !$conn ) {
 180                         return false; // no connection
 181                 }
 182                 $authKey = $this->lockServers[$lockSrv]['authKey'];
 183                 // Build of the command as a flat string...
 184                 $values = implode( '|', $values );
 185                 $key = sha1( $this->session . $action . $type . $values . $authKey );
 186                 // Send out the command...
 187                 if ( fwrite( $conn, "{$this->session}:$key:$action:$type:$values\n" ) === false ) {
 188                         return false;
 189                 }
 190                 // Get the response...
 191                 $response = fgets( $conn );
 192                 if ( $response === false ) {
 193                         return false;
 194                 }
 195                 return trim( $response );
 196         }
 197
 198         /**
 199          * Attempt to acquire locks with the peers for a bucket
 200          *
 201          * @param $bucket integer
 202          * @param $paths Array List of resource keys to lock
 203          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 204          * @return bool|string One of (true, 'cantacquire', 'srverrors')
 205          */
 206         protected function doLockingRequestAll( $bucket, array $paths, $type ) {
 207                 $yesVotes = 0; // locks made on trustable servers
 208                 $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
 209                 $quorum = floor( $votesLeft/2 + 1 ); // simple majority
 210                 // Get votes for each peer, in order, until we have enough...
 211                 foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) {
 212                         // Attempt to acquire the lock on this peer
 213                         if ( !$this->doLockingRequest( $lockSrv, $paths, $type ) ) {
 214                                 return 'cantacquire'; // vetoed; resource locked
 215                         }
 216                         ++$yesVotes; // success for this peer
 217                         if ( $yesVotes >= $quorum ) {
 218                                 return true; // lock obtained
 219                         }
 220                         --$votesLeft;
 221                         $votesNeeded = $quorum - $yesVotes;
 222                         if ( $votesNeeded > $votesLeft ) {
 223                                 // In "trust cache" mode we don't have to meet the quorum
 224                                 break; // short-circuit
 225                         }
 226                 }
 227                 // At this point, we must not have meet the quorum
 228                 return 'srverrors'; // not enough votes to ensure correctness
 229         }
 230
 231         /**
 232          * Get (or reuse) a connection to a lock server
 233          *
 234          * @param $lockSrv string
 235          * @return resource
 236          */
 237         protected function getConnection( $lockSrv ) {
 238                 if ( !isset( $this->conns[$lockSrv] ) ) {
 239                         $cfg = $this->lockServers[$lockSrv];
 240                         wfSuppressWarnings();
 241                         $errno = $errstr = '';
 242                         $conn = fsockopen( $cfg['host'], $cfg['port'], $errno, $errstr, $this->connTimeout );
 243                         wfRestoreWarnings();
 244                         if ( $conn === false ) {
 245                                 return null;
 246                         }
 247                         $sec = floor( $this->connTimeout );
 248                         $usec = floor( ( $this->connTimeout - floor( $this->connTimeout ) ) * 1e6 );
 249                         stream_set_timeout( $conn, $sec, $usec );
 250                         $this->conns[$lockSrv] = $conn;
 251                 }
 252                 return $this->conns[$lockSrv];
 253         }
 254
 255         /**
 256          * Release all locks that this session is holding
 257          *
 258          * @return Status
 259          */
 260         protected function releaseLocks() {
 261                 $status = Status::newGood();
 262                 foreach ( $this->conns as $lockSrv => $conn ) {
 263                         $response = $this->sendCommand( $lockSrv, 'RELEASE_ALL', '', array() );
 264                         if ( $response !== 'RELEASED_ALL' ) {
 265                                 $status->fatal( 'lockmanager-fail-svr-release', $lockSrv );
 266                         }
 267                 }
 268                 return $status;
 269         }
 270
 271         /**
 272          * Get the bucket for resource path.
 273          * This should avoid throwing any exceptions.
 274          *
 275          * @param $path string
 276          * @return integer
 277          */
 278         protected function getBucketFromKey( $path ) {
 279                 $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
 280                 return intval( base_convert( $prefix, 16, 10 ) ) % count( $this->dbsByBucket );
 281         }
 282
 283         /**
 284          * Make sure remaining locks get cleared for sanity
 285          */
 286         function __destruct() {
 287                 $this->releaseLocks();
 288                 foreach ( $this->conns as $conn ) {
 289                         fclose( $conn );
 290                 }
 291         }
 292 }