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                 # Do everything in a transaction as it all gets rolled back eventually
  27                 $db->startAtomic( __CLASS__ );
  28         }
  29
  30         /**
  31          * Get a connection to a lock DB and acquire locks on $paths.
  32          * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
  33          *
  34          * @see DBLockManager::getLocksOnServer()
  35          * @param string $lockSrv
  36          * @param array $paths
  37          * @param string $type
  38          * @return StatusValue
  39          */
  40         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
  41                 $status = StatusValue::newGood();
  42
  43                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
  44
  45                 $keys = []; // list of hash keys for the paths
  46                 $data = []; // list of rows to insert
  47                 $checkEXKeys = []; // list of hash keys that this has no EX lock on
  48                 # Build up values for INSERT clause
  49                 foreach ( $paths as $path ) {
  50                         $key = $this->sha1Base36Absolute( $path );
  51                         $keys[] = $key;
  52                         $data[] = [ 'fls_key' => $key, 'fls_session' => $this->session ];
  53                         if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
  54                                 $checkEXKeys[] = $key;
  55                         }
  56                 }
  57
  58                 # Block new writers (both EX and SH locks leave entries here)...
  59                 $db->insert( 'filelocks_shared', $data, __METHOD__, [ 'IGNORE' ] );
  60                 # Actually do the locking queries...
  61                 if ( $type == self::LOCK_SH ) { // reader locks
  62                         $blocked = false;
  63                         # Bail if there are any existing writers...
  64                         if ( count( $checkEXKeys ) ) {
  65                                 $blocked = $db->selectField( 'filelocks_exclusive', '1',
  66                                         [ 'fle_key' => $checkEXKeys ],
  67                                         __METHOD__
  68                                 );
  69                         }
  70                         # Other prospective writers that haven't yet updated filelocks_exclusive
  71                         # will recheck filelocks_shared after doing so and bail due to this entry.
  72                 } else { // writer locks
  73                         $encSession = $db->addQuotes( $this->session );
  74                         # Bail if there are any existing writers...
  75                         # This may detect readers, but the safe check for them is below.
  76                         # Note: if two writers come at the same time, both bail :)
  77                         $blocked = $db->selectField( 'filelocks_shared', '1',
  78                                 [ 'fls_key' => $keys, "fls_session != $encSession" ],
  79                                 __METHOD__
  80                         );
  81                         if ( !$blocked ) {
  82                                 # Build up values for INSERT clause
  83                                 $data = [];
  84                                 foreach ( $keys as $key ) {
  85                                         $data[] = [ 'fle_key' => $key ];
  86                                 }
  87                                 # Block new readers/writers...
  88                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
  89                                 # Bail if there are any existing readers...
  90                                 $blocked = $db->selectField( 'filelocks_shared', '1',
  91                                         [ 'fls_key' => $keys, "fls_session != $encSession" ],
  92                                         __METHOD__
  93                                 );
  94                         }
  95                 }
  96
  97                 if ( $blocked ) {
  98                         foreach ( $paths as $path ) {
  99                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 100                         }
 101                 }
 102
 103                 return $status;
 104         }
 105
 106         /**
 107          * @see QuorumLockManager::releaseAllLocks()
 108          * @return StatusValue
 109          */
 110         protected function releaseAllLocks() {
 111                 $status = StatusValue::newGood();
 112
 113                 foreach ( $this->conns as $lockDb => $db ) {
 114                         if ( $db->trxLevel() ) { // in transaction
 115                                 try {
 116                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 117                                 } catch ( DBError $e ) {
 118                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 119                                 }
 120                         }
 121                 }
 122
 123                 return $status;
 124         }
 125 }