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                                 $status->fatal( 'lockmanager-fail-acquirelocks', implode( ', ', $paths ) );
  92                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
  93                                 return $status;
  94                         } elseif ( $res !== true ) {
  95                                 // Couldn't contact any servers for this bucket.
  96                                 // Abort and unlock everything we just locked.
  97                                 $status->fatal( 'lockmanager-fail-acquirelocks', implode( ', ', $paths ) );
  98                                 $status->merge( $this->doUnlock( $lockedPaths, $type ) );
  99                                 return $status;
 100                         }
 101                         // Record these locks as active
 102                         foreach ( $paths as $path ) {
 103                                 $this->locksHeld[$path][$type] = 1; // locked
 104                         }
 105                         // Keep track of what locks were made in this attempt
 106                         $lockedPaths = array_merge( $lockedPaths, $paths );
 107                 }
 108
 109                 return $status;
 110         }
 111
 112         protected function doUnlock( array $paths, $type ) {
 113                 $status = Status::newGood();
 114
 115                 foreach ( $paths as $path ) {
 116                         if ( !isset( $this->locksHeld[$path] ) ) {
 117                                 $status->warning( 'lockmanager-notlocked', $path );
 118                         } elseif ( !isset( $this->locksHeld[$path][$type] ) ) {
 119                                 $status->warning( 'lockmanager-notlocked', $path );
 120                         } else {
 121                                 --$this->locksHeld[$path][$type];
 122                                 if ( $this->locksHeld[$path][$type] <= 0 ) {
 123                                         unset( $this->locksHeld[$path][$type] );
 124                                 }
 125                                 if ( !count( $this->locksHeld[$path] ) ) {
 126                                         unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
 127                                 }
 128                         }
 129                 }
 130
 131                 // Reference count the locks held and release locks when zero
 132                 if ( !count( $this->locksHeld ) ) {
 133                         $status->merge( $this->releaseLocks() );
 134                 }
 135
 136                 return $status;
 137         }
 138
 139         /**
 140          * Get a connection to a lock server and acquire locks on $paths
 141          *
 142          * @param $lockSrv string
 143          * @param $paths Array
 144          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 145          * @return bool Resources able to be locked
 146          */
 147         protected function doLockingRequest( $lockSrv, array $paths, $type ) {
 148                 if ( $type == self::LOCK_SH ) { // reader locks
 149                         $type = 'SH';
 150                 } elseif ( $type == self::LOCK_EX ) { // writer locks
 151                         $type = 'EX';
 152                 } else {
 153                         return true; // ok...
 154                 }
 155
 156                 // Send out the command and get the response...
 157                 $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
 158                 $response = $this->sendCommand( $lockSrv, 'ACQUIRE', $type, $keys );
 159
 160                 return ( $response === 'ACQUIRED' );
 161         }
 162
 163         /**
 164          * Send a command and get back the response
 165          *
 166          * @param $lockSrv string
 167          * @param $action string
 168          * @param $type string
 169          * @param $values Array
 170          * @return string|false
 171          */
 172         protected function sendCommand( $lockSrv, $action, $type, $values ) {
 173                 $conn = $this->getConnection( $lockSrv );
 174                 if ( !$conn ) {
 175                         return false; // no connection
 176                 }
 177                 $authKey = $this->lockServers[$lockSrv]['authKey'];
 178                 // Build of the command as a flat string...
 179                 $values = implode( '|', $values );
 180                 $key = sha1( $this->session . $action . $type . $values . $authKey );
 181                 // Send out the command...
 182                 if ( fwrite( $conn, "{$this->session}:$key:$action:$type:$values\n" ) === false ) {
 183                         return false;
 184                 }
 185                 // Get the response...
 186                 $response = fgets( $conn );
 187                 if ( $response === false ) {
 188                         return false;
 189                 }
 190                 return trim( $response );
 191         }
 192
 193         /**
 194          * Attempt to acquire locks with the peers for a bucket
 195          *
 196          * @param $bucket integer
 197          * @param $paths Array List of resource keys to lock
 198          * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
 199          * @return bool|string One of (true, 'cantacquire', 'srverrors')
 200          */
 201         protected function doLockingRequestAll( $bucket, array $paths, $type ) {
 202                 $yesVotes = 0; // locks made on trustable servers
 203                 $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
 204                 $quorum = floor( $votesLeft/2 + 1 ); // simple majority
 205                 // Get votes for each peer, in order, until we have enough...
 206                 foreach ( $this->srvsByBucket[$bucket] as $index => $lockSrv ) {
 207                         // Attempt to acquire the lock on this peer
 208                         if ( !$this->doLockingRequest( $lockSrv, $paths, $type ) ) {
 209                                 return 'cantacquire'; // vetoed; resource locked
 210                         }
 211                         ++$yesVotes; // success for this peer
 212                         if ( $yesVotes >= $quorum ) {
 213                                 return true; // lock obtained
 214                         }
 215                         --$votesLeft;
 216                         $votesNeeded = $quorum - $yesVotes;
 217                         if ( $votesNeeded > $votesLeft ) {
 218                                 // In "trust cache" mode we don't have to meet the quorum
 219                                 break; // short-circuit
 220                         }
 221                 }
 222                 // At this point, we must not have meet the quorum
 223                 return 'srverrors'; // not enough votes to ensure correctness
 224         }
 225
 226         /**
 227          * Get (or reuse) a connection to a lock server
 228          *
 229          * @param $lockSrv string
 230          * @return resource
 231          */
 232         protected function getConnection( $lockSrv ) {
 233                 if ( !isset( $this->conns[$lockSrv] ) ) {
 234                         $cfg = $this->lockServers[$lockSrv];
 235                         wfSuppressWarnings();
 236                         $errno = $errstr = '';
 237                         $conn = fsockopen( $cfg['host'], $cfg['port'], $errno, $errstr, $this->connTimeout );
 238                         wfRestoreWarnings();
 239                         if ( $conn === false ) {
 240                                 return null;
 241                         }
 242                         $sec = floor( $this->connTimeout );
 243                         $usec = floor( ( $this->connTimeout - floor( $this->connTimeout ) ) * 1e6 );
 244                         stream_set_timeout( $conn, $sec, $usec );
 245                         $this->conns[$lockSrv] = $conn;
 246                 }
 247                 return $this->conns[$lockSrv];
 248         }
 249
 250         /**
 251          * Release all locks that this session is holding
 252          *
 253          * @return Status
 254          */
 255         protected function releaseLocks() {
 256                 $status = Status::newGood();
 257                 foreach ( $this->conns as $lockSrv => $conn ) {
 258                         $response = $this->sendCommand( $lockSrv, 'RELEASE_ALL', '', array() );
 259                         if ( $response !== 'RELEASED_ALL' ) {
 260                                 $status->fatal( 'lockmanager-fail-svr-release', $lockSrv );
 261                         }
 262                 }
 263                 return $status;
 264         }
 265
 266         /**
 267          * Get the bucket for resource path.
 268          * This should avoid throwing any exceptions.
 269          *
 270          * @param $path string
 271          * @return integer
 272          */
 273         protected function getBucketFromKey( $path ) {
 274                 $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
 275                 return intval( base_convert( $prefix, 16, 10 ) ) % count( $this->dbsByBucket );
 276         }
 277
 278         /**
 279          * Make sure remaining locks get cleared for sanity
 280          */
 281         function __destruct() {
 282                 $this->releaseLocks();
 283                 foreach ( $this->conns as $lockSrv => $conn ) {
 284                         fclose( $conn );
 285                 }
 286         }
 287 }