includes/filebackend/lockmanager/MySqlLockManager.php

   1 <?php
   2 /**
   3  * MySQL version of DBLockManager that supports shared locks.
   4  *
   5  * All lock servers must have the innodb table defined in locking/filelocks.sql.
   6  * All locks are non-blocking, which avoids deadlocks.
   7  *
   8  * @ingroup LockManager
   9  */
  10 class MySqlLockManager extends DBLockManager {
  11         /** @var array Mapping of lock types to the type actually used */
  12         protected $lockTypeMap = [
  13                 self::LOCK_SH => self::LOCK_SH,
  14                 self::LOCK_UW => self::LOCK_SH,
  15                 self::LOCK_EX => self::LOCK_EX
  16         ];
  17
  18         protected function initConnection( $lockDb, IDatabase $db ) {
  19                 # Let this transaction see lock rows from other transactions
  20                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
  21                 # Do everything in a transaction as it all gets rolled back eventually
  22                 $db->startAtomic( __CLASS__ );
  23         }
  24
  25         /**
  26          * Get a connection to a lock DB and acquire locks on $paths.
  27          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
  28          *
  29          * @see DBLockManager::getLocksOnServer()
  30          * @param string $lockSrv
  31          * @param array $paths
  32          * @param string $type
  33          * @return StatusValue
  34          */
  35         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
  36                 $status = StatusValue::newGood();
  37
  38                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
  39
  40                 $keys = []; // list of hash keys for the paths
  41                 $data = []; // list of rows to insert
  42                 $checkEXKeys = []; // list of hash keys that this has no EX lock on
  43                 # Build up values for INSERT clause
  44                 foreach ( $paths as $path ) {
  45                         $key = $this->sha1Base36Absolute( $path );
  46                         $keys[] = $key;
  47                         $data[] = [ 'fls_key' => $key, 'fls_session' => $this->session ];
  48                         if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
  49                                 $checkEXKeys[] = $key;
  50                         }
  51                 }
  52
  53                 # Block new writers (both EX and SH locks leave entries here)...
  54                 $db->insert( 'filelocks_shared', $data, __METHOD__, [ 'IGNORE' ] );
  55                 # Actually do the locking queries...
  56                 if ( $type == self::LOCK_SH ) { // reader locks
  57                         $blocked = false;
  58                         # Bail if there are any existing writers...
  59                         if ( count( $checkEXKeys ) ) {
  60                                 $blocked = $db->selectField( 'filelocks_exclusive', '1',
  61                                         [ 'fle_key' => $checkEXKeys ],
  62                                         __METHOD__
  63                                 );
  64                         }
  65                         # Other prospective writers that haven't yet updated filelocks_exclusive
  66                         # will recheck filelocks_shared after doing so and bail due to this entry.
  67                 } else { // writer locks
  68                         $encSession = $db->addQuotes( $this->session );
  69                         # Bail if there are any existing writers...
  70                         # This may detect readers, but the safe check for them is below.
  71                         # Note: if two writers come at the same time, both bail :)
  72                         $blocked = $db->selectField( 'filelocks_shared', '1',
  73                                 [ 'fls_key' => $keys, "fls_session != $encSession" ],
  74                                 __METHOD__
  75                         );
  76                         if ( !$blocked ) {
  77                                 # Build up values for INSERT clause
  78                                 $data = [];
  79                                 foreach ( $keys as $key ) {
  80                                         $data[] = [ 'fle_key' => $key ];
  81                                 }
  82                                 # Block new readers/writers...
  83                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
  84                                 # Bail if there are any existing readers...
  85                                 $blocked = $db->selectField( 'filelocks_shared', '1',
  86                                         [ 'fls_key' => $keys, "fls_session != $encSession" ],
  87                                         __METHOD__
  88                                 );
  89                         }
  90                 }
  91
  92                 if ( $blocked ) {
  93                         foreach ( $paths as $path ) {
  94                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
  95                         }
  96                 }
  97
  98                 return $status;
  99         }
 100
 101         /**
 102          * @see QuorumLockManager::releaseAllLocks()
 103          * @return StatusValue
 104          */
 105         protected function releaseAllLocks() {
 106                 $status = StatusValue::newGood();
 107
 108                 foreach ( $this->conns as $lockDb => $db ) {
 109                         if ( $db->trxLevel() ) { // in transaction
 110                                 try {
 111                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 112                                 } catch ( DBError $e ) {
 113                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 114                                 }
 115                         }
 116                 }
 117
 118                 return $status;
 119         }
 120 }