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