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 getLocalLB() {
  19                 // Use a separate connection so releaseAllLocks() doesn't rollback the main trx
  20                 return wfGetLBFactory()->newMainLB( $this->domain );
  21         }
  22
  23         protected function initConnection( $lockDb, IDatabase $db ) {
  24                 # Let this transaction see lock rows from other transactions
  25                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
  26         }
  27
  28         /**
  29          * Get a connection to a lock DB and acquire locks on $paths.
  30          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
  31          *
  32          * @see DBLockManager::getLocksOnServer()
  33          * @param string $lockSrv
  34          * @param array $paths
  35          * @param string $type
  36          * @return Status
  37          */
  38         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
  39                 $status = Status::newGood();
  40
  41                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
  42
  43                 $keys = []; // list of hash keys for the paths
  44                 $data = []; // list of rows to insert
  45                 $checkEXKeys = []; // list of hash keys that this has no EX lock on
  46                 # Build up values for INSERT clause
  47                 foreach ( $paths as $path ) {
  48                         $key = $this->sha1Base36Absolute( $path );
  49                         $keys[] = $key;
  50                         $data[] = [ 'fls_key' => $key, 'fls_session' => $this->session ];
  51                         if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
  52                                 $checkEXKeys[] = $key;
  53                         }
  54                 }
  55
  56                 # Block new writers (both EX and SH locks leave entries here)...
  57                 $db->insert( 'filelocks_shared', $data, __METHOD__, [ 'IGNORE' ] );
  58                 # Actually do the locking queries...
  59                 if ( $type == self::LOCK_SH ) { // reader locks
  60                         $blocked = false;
  61                         # Bail if there are any existing writers...
  62                         if ( count( $checkEXKeys ) ) {
  63                                 $blocked = $db->selectField( 'filelocks_exclusive', '1',
  64                                         [ 'fle_key' => $checkEXKeys ],
  65                                         __METHOD__
  66                                 );
  67                         }
  68                         # Other prospective writers that haven't yet updated filelocks_exclusive
  69                         # will recheck filelocks_shared after doing so and bail due to this entry.
  70                 } else { // writer locks
  71                         $encSession = $db->addQuotes( $this->session );
  72                         # Bail if there are any existing writers...
  73                         # This may detect readers, but the safe check for them is below.
  74                         # Note: if two writers come at the same time, both bail :)
  75                         $blocked = $db->selectField( 'filelocks_shared', '1',
  76                                 [ 'fls_key' => $keys, "fls_session != $encSession" ],
  77                                 __METHOD__
  78                         );
  79                         if ( !$blocked ) {
  80                                 # Build up values for INSERT clause
  81                                 $data = [];
  82                                 foreach ( $keys as $key ) {
  83                                         $data[] = [ 'fle_key' => $key ];
  84                                 }
  85                                 # Block new readers/writers...
  86                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
  87                                 # Bail if there are any existing readers...
  88                                 $blocked = $db->selectField( 'filelocks_shared', '1',
  89                                         [ 'fls_key' => $keys, "fls_session != $encSession" ],
  90                                         __METHOD__
  91                                 );
  92                         }
  93                 }
  94
  95                 if ( $blocked ) {
  96                         foreach ( $paths as $path ) {
  97                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
  98                         }
  99                 }
 100
 101                 return $status;
 102         }
 103
 104         /**
 105          * @see QuorumLockManager::releaseAllLocks()
 106          * @return Status
 107          */
 108         protected function releaseAllLocks() {
 109                 $status = Status::newGood();
 110
 111                 foreach ( $this->conns as $lockDb => $db ) {
 112                         if ( $db->trxLevel() ) { // in transaction
 113                                 try {
 114                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 115                                 } catch ( DBError $e ) {
 116                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 117                                 }
 118                         }
 119                 }
 120
 121                 return $status;
 122         }
 123 }