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