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| 1 | <?php |
| 2 | /** |
| 3 | * @license GPL-2.0-or-later |
| 4 | * @file |
| 5 | */ |
| 6 | namespace Wikimedia\LockManager; |
| 7 | |
| 8 | use StatusValue; |
| 9 | use Wikimedia\ArrayUtils\ArrayUtils; |
| 10 | |
| 11 | /** |
| 12 | * Base class for lock managers that use a quorum of peer servers for locks. |
| 13 | * |
| 14 | * The resource space can also be sharded into separate peer groups. |
| 15 | * |
| 16 | * See MemcLockManager and RedisLockManager. |
| 17 | * |
| 18 | * @stable to extend |
| 19 | * @ingroup LockManager |
| 20 | * @since 1.20 |
| 21 | */ |
| 22 | abstract class QuorumLockManager extends LockManager { |
| 23 | /** @var array Map server names to data used by subclasses */ |
| 24 | protected $lockServers = []; |
| 25 | /** @var array list of down server names */ |
| 26 | protected $downServers = []; |
| 27 | /** @var int Minimum number of success to consider lock/unlock successful */ |
| 28 | protected $minVotes = 2; |
| 29 | |
| 30 | /** @inheritDoc */ |
| 31 | final protected function doLockByType( array $pathsByType ) { |
| 32 | $status = StatusValue::newGood(); |
| 33 | $lockedPaths = []; // files locked in this attempt (type => paths) |
| 34 | foreach ( $pathsByType as $type => $paths ) { |
| 35 | foreach ( $paths as $path ) { |
| 36 | if ( isset( $this->locksHeld[$path][$type] ) ) { |
| 37 | ++$this->locksHeld[$path][$type]; |
| 38 | } else { |
| 39 | $lockedPaths[$type][] = $path; |
| 40 | $status->merge( $this->doLockingRequest( $path, $type ) ); |
| 41 | if ( !$status->isOK() ) { |
| 42 | $status->merge( $this->doUnlockByType( $lockedPaths ) ); |
| 43 | return $status; |
| 44 | } else { |
| 45 | $this->locksHeld[$path][$type] = 1; // locked |
| 46 | } |
| 47 | } |
| 48 | } |
| 49 | } |
| 50 | |
| 51 | return $status; |
| 52 | } |
| 53 | |
| 54 | /** |
| 55 | * @stable to override |
| 56 | * |
| 57 | * @param array $pathsByType |
| 58 | * |
| 59 | * @return StatusValue |
| 60 | */ |
| 61 | protected function doUnlockByType( array $pathsByType ) { |
| 62 | $status = StatusValue::newGood(); |
| 63 | |
| 64 | foreach ( $pathsByType as $type => $paths ) { |
| 65 | foreach ( $paths as $path ) { |
| 66 | if ( !isset( $this->locksHeld[$path][$type] ) ) { |
| 67 | $status->warning( 'lockmanager-notlocked', $path ); |
| 68 | } else { |
| 69 | --$this->locksHeld[$path][$type]; |
| 70 | // Reference count the locks held and release locks when zero |
| 71 | if ( $this->locksHeld[$path][$type] <= 0 ) { |
| 72 | $status->merge( $this->doUnlockingRequest( $path, $type ) ); |
| 73 | unset( $this->locksHeld[$path][$type] ); |
| 74 | } |
| 75 | if ( $this->locksHeld[$path] === [] ) { |
| 76 | unset( $this->locksHeld[$path] ); // no SH or EX locks left for key |
| 77 | } |
| 78 | } |
| 79 | } |
| 80 | } |
| 81 | |
| 82 | if ( $this->locksHeld === [] ) { |
| 83 | $status->merge( $this->releaseAllLocks() ); |
| 84 | } |
| 85 | |
| 86 | return $status; |
| 87 | } |
| 88 | |
| 89 | /** |
| 90 | * Attempt to acquire locks with the peers. |
| 91 | * This is all or nothing; if any key is locked then this totally fails. |
| 92 | * |
| 93 | * @param string $path path to be locked |
| 94 | * @param string $type type of lock to be passed to ::getLocksOnServer() |
| 95 | * @return StatusValue |
| 96 | */ |
| 97 | final protected function doLockingRequest( string $path, string $type ) { |
| 98 | $status = StatusValue::newGood(); |
| 99 | $yesVotes = 0; // locks made on trustable servers |
| 100 | $votesLeft = count( $this->lockServers ); // remaining peers |
| 101 | $sortedServers = array_keys( $this->lockServers ); |
| 102 | // shuffle the servers based on hashing of the keys |
| 103 | ArrayUtils::consistentHashSort( $sortedServers, $path ); |
| 104 | $minVotes = min( $this->minVotes, count( $this->lockServers ) ); |
| 105 | foreach ( $sortedServers as $lockServer ) { |
| 106 | if ( !$this->isServerUp( $lockServer ) ) { |
| 107 | --$votesLeft; |
| 108 | $status->warning( 'lockmanager-fail-svr-acquire', $lockServer ); |
| 109 | $this->downServers[$lockServer] = time(); |
| 110 | continue; |
| 111 | } |
| 112 | $status->merge( $this->getLocksOnServer( $lockServer, [ $type => [ $path ] ] ) ); |
| 113 | if ( !$status->isOK() ) { |
| 114 | return $status; // vetoed; resource locked |
| 115 | } |
| 116 | ++$yesVotes; // success for this peer |
| 117 | if ( $yesVotes >= $minVotes ) { |
| 118 | return $status; // lock obtained |
| 119 | } |
| 120 | --$votesLeft; |
| 121 | $votesNeeded = $minVotes - $yesVotes; |
| 122 | if ( $votesNeeded > $votesLeft ) { |
| 123 | break; // short-circuit |
| 124 | } |
| 125 | } |
| 126 | // At this point, we must not have met the quorum |
| 127 | $status->setResult( false ); |
| 128 | |
| 129 | return $status; |
| 130 | } |
| 131 | |
| 132 | /** |
| 133 | * Attempt to release locks with the peers |
| 134 | * |
| 135 | * @param string $path the path to be unlocked |
| 136 | * @param string $type the type to be passed to ::freeLocksOnServer() |
| 137 | * @return StatusValue |
| 138 | */ |
| 139 | final protected function doUnlockingRequest( string $path, string $type ) { |
| 140 | $status = StatusValue::newGood(); |
| 141 | |
| 142 | $yesVotes = 0; // locks freed on trustable servers |
| 143 | $isDegraded = count( $this->downServers ); // not the normal quorum? |
| 144 | $sortedServers = array_keys( $this->lockServers ); |
| 145 | // shuffle the servers based on hashing of the keys |
| 146 | ArrayUtils::consistentHashSort( $sortedServers, $path ); |
| 147 | $minVotes = min( $this->minVotes, count( $this->lockServers ) ); |
| 148 | foreach ( $sortedServers as $lockServer ) { |
| 149 | if ( !$this->isServerUp( $lockServer ) ) { |
| 150 | $status->warning( 'lockmanager-fail-svr-release', $lockServer ); |
| 151 | } else { |
| 152 | // Attempt to release the lock on this peer |
| 153 | $status->merge( $this->freeLocksOnServer( $lockServer, [ $type => [ $path ] ] ) ); |
| 154 | ++$yesVotes; // success for this peer |
| 155 | // Normally the first peers form the quorum, and the others are ignored. |
| 156 | // Ignore them in this case, but not when an alternative quorum was used. |
| 157 | if ( $yesVotes >= $minVotes && !$isDegraded ) { |
| 158 | break; // lock released |
| 159 | } |
| 160 | } |
| 161 | } |
| 162 | |
| 163 | // Set a bad StatusValue if the quorum was not met. |
| 164 | // Assumes the same "up" servers as during the acquire step. |
| 165 | $status->setResult( $yesVotes >= $minVotes ); |
| 166 | |
| 167 | return $status; |
| 168 | } |
| 169 | |
| 170 | /** |
| 171 | * Check if a lock server is up. |
| 172 | * This should process cache results to reduce RTT. |
| 173 | * |
| 174 | * @param string $lockServer |
| 175 | * @return bool |
| 176 | */ |
| 177 | abstract protected function isServerUp( $lockServer ); |
| 178 | |
| 179 | /** |
| 180 | * Get a connection to a lock server and acquire locks |
| 181 | * |
| 182 | * @param string $lockServer |
| 183 | * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths |
| 184 | * @return StatusValue |
| 185 | */ |
| 186 | abstract protected function getLocksOnServer( $lockServer, array $pathsByType ); |
| 187 | |
| 188 | /** |
| 189 | * Get a connection to a lock server and release locks on $paths. |
| 190 | * |
| 191 | * Subclasses must effectively implement this or releaseAllLocks(). |
| 192 | * |
| 193 | * @param string $lockServer |
| 194 | * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths |
| 195 | * @return StatusValue |
| 196 | */ |
| 197 | abstract protected function freeLocksOnServer( $lockServer, array $pathsByType ); |
| 198 | |
| 199 | /** |
| 200 | * Release all locks that this session is holding. |
| 201 | * |
| 202 | * Subclasses must effectively implement this or freeLocksOnServer(). |
| 203 | * |
| 204 | * @return StatusValue |
| 205 | */ |
| 206 | abstract protected function releaseAllLocks(); |
| 207 | } |
| 208 | /** @deprecated class alias since 1.46 */ |
| 209 | class_alias( QuorumLockManager::class, 'QuorumLockManager' ); |