includes/filebackend/lockmanager/MySqlLockManager.php

   1 <?php
   2 /**
   3  * MySQL version of DBLockManager that supports shared locks.
   4  *
   5  * Do NOT use this on connection handles that are also being used for anything
   6  * else as the transaction isolation will be wrong and all the other changes will
   7  * get rolled back when the locks release!
   8  *
   9  * All lock servers must have the innodb table defined in maintenance/locking/filelocks.sql.
  10  * All locks are non-blocking, which avoids deadlocks.
  11  *
  12  * @ingroup LockManager
  13  */
  14 class MySqlLockManager extends DBLockManager {
  15         /** @var array Mapping of lock types to the type actually used */
  16         protected $lockTypeMap = [
  17                 self::LOCK_SH => self::LOCK_SH,
  18                 self::LOCK_UW => self::LOCK_SH,
  19                 self::LOCK_EX => self::LOCK_EX
  20         ];
  21
  22         public function __construct( array $config ) {
  23                 parent::__construct( $config );
  24
  25                 $this->session = substr( $this->session, 0, 31 ); // fit to field
  26         }
  27
  28         protected function initConnection( $lockDb, IDatabase $db ) {
  29                 # Let this transaction see lock rows from other transactions
  30                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
  31                 # Do everything in a transaction as it all gets rolled back eventually
  32                 $db->startAtomic( __CLASS__ );
  33         }
  34
  35         /**
  36          * Get a connection to a lock DB and acquire locks on $paths.
  37          * This does not use GET_LOCK() per https://bugs.mysql.com/bug.php?id=1118.
  38          *
  39          * @see DBLockManager::getLocksOnServer()
  40          * @param string $lockSrv
  41          * @param array $paths
  42          * @param string $type
  43          * @return StatusValue
  44          */
  45         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
  46                 $status = StatusValue::newGood();
  47
  48                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
  49
  50                 $keys = []; // list of hash keys for the paths
  51                 $data = []; // list of rows to insert
  52                 $checkEXKeys = []; // list of hash keys that this has no EX lock on
  53                 # Build up values for INSERT clause
  54                 foreach ( $paths as $path ) {
  55                         $key = $this->sha1Base36Absolute( $path );
  56                         $keys[] = $key;
  57                         $data[] = [ 'fls_key' => $key, 'fls_session' => $this->session ];
  58                         if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
  59                                 $checkEXKeys[] = $key; // this has no EX lock on $key itself
  60                         }
  61                 }
  62
  63                 # Block new writers (both EX and SH locks leave entries here)...
  64                 $db->insert( 'filelocks_shared', $data, __METHOD__, [ 'IGNORE' ] );
  65                 # Actually do the locking queries...
  66                 if ( $type == self::LOCK_SH ) { // reader locks
  67                         # Bail if there are any existing writers...
  68                         if ( count( $checkEXKeys ) ) {
  69                                 $blocked = $db->selectField(
  70                                         'filelocks_exclusive',
  71                                         '1',
  72                                         [ 'fle_key' => $checkEXKeys ],
  73                                         __METHOD__
  74                                 );
  75                         } else {
  76                                 $blocked = false;
  77                         }
  78                         # Other prospective writers that haven't yet updated filelocks_exclusive
  79                         # will recheck filelocks_shared after doing so and bail due to this entry.
  80                 } else { // writer locks
  81                         $encSession = $db->addQuotes( $this->session );
  82                         # Bail if there are any existing writers...
  83                         # This may detect readers, but the safe check for them is below.
  84                         # Note: if two writers come at the same time, both bail :)
  85                         $blocked = $db->selectField(
  86                                 'filelocks_shared',
  87                                 '1',
  88                                 [ 'fls_key' => $keys, "fls_session != $encSession" ],
  89                                 __METHOD__
  90                         );
  91                         if ( !$blocked ) {
  92                                 # Build up values for INSERT clause
  93                                 $data = [];
  94                                 foreach ( $keys as $key ) {
  95                                         $data[] = [ 'fle_key' => $key ];
  96                                 }
  97                                 # Block new readers/writers...
  98                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
  99                                 # Bail if there are any existing readers...
 100                                 $blocked = $db->selectField(
 101                                         'filelocks_shared',
 102                                         '1',
 103                                         [ 'fls_key' => $keys, "fls_session != $encSession" ],
 104                                         __METHOD__
 105                                 );
 106                         }
 107                 }
 108
 109                 if ( $blocked ) {
 110                         foreach ( $paths as $path ) {
 111                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 112                         }
 113                 }
 114
 115                 return $status;
 116         }
 117
 118         /**
 119          * @see QuorumLockManager::releaseAllLocks()
 120          * @return StatusValue
 121          */
 122         protected function releaseAllLocks() {
 123                 $status = StatusValue::newGood();
 124
 125                 foreach ( $this->conns as $lockDb => $db ) {
 126                         if ( $db->trxLevel() ) { // in transaction
 127                                 try {
 128                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 129                                 } catch ( DBError $e ) {
 130                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 131                                 }
 132                         }
 133                 }
 134
 135                 return $status;
 136         }
 137 }