includes/filebackend/lockmanager/MySqlLockManager.php

   1 <?php
   2
   3 use Wikimedia\Rdbms\IDatabase;
   4 use Wikimedia\Rdbms\DBError;
   5
   6 /**
   7  * MySQL version of DBLockManager that supports shared locks.
   8  *
   9  * Do NOT use this on connection handles that are also being used for anything
  10  * else as the transaction isolation will be wrong and all the other changes will
  11  * get rolled back when the locks release!
  12  *
  13  * All lock servers must have the innodb table defined in maintenance/locking/filelocks.sql.
  14  * All locks are non-blocking, which avoids deadlocks.
  15  *
  16  * @ingroup LockManager
  17  */
  18 class MySqlLockManager extends DBLockManager {
  19         /** @var array Mapping of lock types to the type actually used */
  20         protected $lockTypeMap = [
  21                 self::LOCK_SH => self::LOCK_SH,
  22                 self::LOCK_UW => self::LOCK_SH,
  23                 self::LOCK_EX => self::LOCK_EX
  24         ];
  25
  26         public function __construct( array $config ) {
  27                 parent::__construct( $config );
  28
  29                 $this->session = substr( $this->session, 0, 31 ); // fit to field
  30         }
  31
  32         protected function initConnection( $lockDb, IDatabase $db ) {
  33                 # Let this transaction see lock rows from other transactions
  34                 $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
  35                 # Do everything in a transaction as it all gets rolled back eventually
  36                 $db->startAtomic( __CLASS__ );
  37         }
  38
  39         /**
  40          * Get a connection to a lock DB and acquire locks on $paths.
  41          * This does not use GET_LOCK() per https://bugs.mysql.com/bug.php?id=1118.
  42          *
  43          * @see DBLockManager::getLocksOnServer()
  44          * @param string $lockSrv
  45          * @param array $paths
  46          * @param string $type
  47          * @return StatusValue
  48          */
  49         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
  50                 $status = StatusValue::newGood();
  51
  52                 $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
  53
  54                 $keys = []; // list of hash keys for the paths
  55                 $data = []; // list of rows to insert
  56                 $checkEXKeys = []; // list of hash keys that this has no EX lock on
  57                 # Build up values for INSERT clause
  58                 foreach ( $paths as $path ) {
  59                         $key = $this->sha1Base36Absolute( $path );
  60                         $keys[] = $key;
  61                         $data[] = [ 'fls_key' => $key, 'fls_session' => $this->session ];
  62                         if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
  63                                 $checkEXKeys[] = $key; // this has no EX lock on $key itself
  64                         }
  65                 }
  66
  67                 # Block new writers (both EX and SH locks leave entries here)...
  68                 $db->insert( 'filelocks_shared', $data, __METHOD__, [ 'IGNORE' ] );
  69                 # Actually do the locking queries...
  70                 if ( $type == self::LOCK_SH ) { // reader locks
  71                         # Bail if there are any existing writers...
  72                         if ( count( $checkEXKeys ) ) {
  73                                 $blocked = $db->selectField(
  74                                         'filelocks_exclusive',
  75                                         '1',
  76                                         [ 'fle_key' => $checkEXKeys ],
  77                                         __METHOD__
  78                                 );
  79                         } else {
  80                                 $blocked = false;
  81                         }
  82                         # Other prospective writers that haven't yet updated filelocks_exclusive
  83                         # will recheck filelocks_shared after doing so and bail due to this entry.
  84                 } else { // writer locks
  85                         $encSession = $db->addQuotes( $this->session );
  86                         # Bail if there are any existing writers...
  87                         # This may detect readers, but the safe check for them is below.
  88                         # Note: if two writers come at the same time, both bail :)
  89                         $blocked = $db->selectField(
  90                                 'filelocks_shared',
  91                                 '1',
  92                                 [ 'fls_key' => $keys, "fls_session != $encSession" ],
  93                                 __METHOD__
  94                         );
  95                         if ( !$blocked ) {
  96                                 # Build up values for INSERT clause
  97                                 $data = [];
  98                                 foreach ( $keys as $key ) {
  99                                         $data[] = [ 'fle_key' => $key ];
 100                                 }
 101                                 # Block new readers/writers...
 102                                 $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
 103                                 # Bail if there are any existing readers...
 104                                 $blocked = $db->selectField(
 105                                         'filelocks_shared',
 106                                         '1',
 107                                         [ 'fls_key' => $keys, "fls_session != $encSession" ],
 108                                         __METHOD__
 109                                 );
 110                         }
 111                 }
 112
 113                 if ( $blocked ) {
 114                         foreach ( $paths as $path ) {
 115                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 116                         }
 117                 }
 118
 119                 return $status;
 120         }
 121
 122         /**
 123          * @see QuorumLockManager::releaseAllLocks()
 124          * @return StatusValue
 125          */
 126         protected function releaseAllLocks() {
 127                 $status = StatusValue::newGood();
 128
 129                 foreach ( $this->conns as $lockDb => $db ) {
 130                         if ( $db->trxLevel() ) { // in transaction
 131                                 try {
 132                                         $db->rollback( __METHOD__ ); // finish transaction and kill any rows
 133                                 } catch ( DBError $e ) {
 134                                         $status->fatal( 'lockmanager-fail-db-release', $lockDb );
 135                                 }
 136                         }
 137                 }
 138
 139                 return $status;
 140         }
 141 }