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| 1 | <?php |
| 2 | /** |
| 3 | * This program is free software; you can redistribute it and/or modify |
| 4 | * it under the terms of the GNU General Public License as published by |
| 5 | * the Free Software Foundation; either version 2 of the License, or |
| 6 | * (at your option) any later version. |
| 7 | * |
| 8 | * This program is distributed in the hope that it will be useful, |
| 9 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 10 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 11 | * GNU General Public License for more details. |
| 12 | * |
| 13 | * You should have received a copy of the GNU General Public License along |
| 14 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 15 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
| 16 | * http://www.gnu.org/copyleft/gpl.html |
| 17 | * |
| 18 | * @file |
| 19 | */ |
| 20 | |
| 21 | /** |
| 22 | * Base class for lock managers that use a quorum of peer servers for locks. |
| 23 | * |
| 24 | * The resource space can also be sharded into separate peer groups. |
| 25 | * |
| 26 | * See MemcLockManager and RedisLockManager. |
| 27 | * |
| 28 | * @stable to extend |
| 29 | * @ingroup LockManager |
| 30 | * @since 1.20 |
| 31 | */ |
| 32 | abstract class QuorumLockManager extends LockManager { |
| 33 | /** @var array Map of bucket indexes to peer server lists */ |
| 34 | protected $srvsByBucket = []; // (bucket index => (lsrv1, lsrv2, ...)) |
| 35 | |
| 36 | /** @var array Map of degraded buckets */ |
| 37 | protected $degradedBuckets = []; // (bucket index => UNIX timestamp) |
| 38 | |
| 39 | final protected function doLockByType( array $pathsByType ) { |
| 40 | $status = StatusValue::newGood(); |
| 41 | |
| 42 | $pathsByTypeByBucket = []; // (bucket => type => paths) |
| 43 | // Get locks that need to be acquired (buckets => locks)... |
| 44 | foreach ( $pathsByType as $type => $paths ) { |
| 45 | foreach ( $paths as $path ) { |
| 46 | if ( isset( $this->locksHeld[$path][$type] ) ) { |
| 47 | ++$this->locksHeld[$path][$type]; |
| 48 | } else { |
| 49 | $bucket = $this->getBucketFromPath( $path ); |
| 50 | $pathsByTypeByBucket[$bucket][$type][] = $path; |
| 51 | } |
| 52 | } |
| 53 | } |
| 54 | |
| 55 | // Acquire locks in each bucket in bucket order to reduce contention. Any blocking |
| 56 | // mutexes during the acquisition step will not involve circular waiting on buckets. |
| 57 | ksort( $pathsByTypeByBucket ); |
| 58 | |
| 59 | $lockedPaths = []; // files locked in this attempt (type => paths) |
| 60 | // Attempt to acquire these locks... |
| 61 | foreach ( $pathsByTypeByBucket as $bucket => $bucketPathsByType ) { |
| 62 | // Try to acquire the locks for this bucket |
| 63 | $status->merge( $this->doLockingRequestBucket( $bucket, $bucketPathsByType ) ); |
| 64 | if ( !$status->isOK() ) { |
| 65 | $status->merge( $this->doUnlockByType( $lockedPaths ) ); |
| 66 | |
| 67 | return $status; |
| 68 | } |
| 69 | // Record these locks as active |
| 70 | foreach ( $bucketPathsByType as $type => $paths ) { |
| 71 | foreach ( $paths as $path ) { |
| 72 | $this->locksHeld[$path][$type] = 1; // locked |
| 73 | // Keep track of what locks were made in this attempt |
| 74 | $lockedPaths[$type][] = $path; |
| 75 | } |
| 76 | } |
| 77 | } |
| 78 | |
| 79 | return $status; |
| 80 | } |
| 81 | |
| 82 | /** |
| 83 | * @stable to override |
| 84 | * |
| 85 | * @param array $pathsByType |
| 86 | * |
| 87 | * @return StatusValue |
| 88 | */ |
| 89 | protected function doUnlockByType( array $pathsByType ) { |
| 90 | $status = StatusValue::newGood(); |
| 91 | |
| 92 | $pathsByTypeByBucket = []; // (bucket => type => paths) |
| 93 | foreach ( $pathsByType as $type => $paths ) { |
| 94 | foreach ( $paths as $path ) { |
| 95 | if ( !isset( $this->locksHeld[$path][$type] ) ) { |
| 96 | $status->warning( 'lockmanager-notlocked', $path ); |
| 97 | } else { |
| 98 | --$this->locksHeld[$path][$type]; |
| 99 | // Reference count the locks held and release locks when zero |
| 100 | if ( $this->locksHeld[$path][$type] <= 0 ) { |
| 101 | unset( $this->locksHeld[$path][$type] ); |
| 102 | $bucket = $this->getBucketFromPath( $path ); |
| 103 | $pathsByTypeByBucket[$bucket][$type][] = $path; |
| 104 | } |
| 105 | if ( $this->locksHeld[$path] === [] ) { |
| 106 | unset( $this->locksHeld[$path] ); // no SH or EX locks left for key |
| 107 | } |
| 108 | } |
| 109 | } |
| 110 | } |
| 111 | |
| 112 | // Remove these specific locks if possible, or at least release |
| 113 | // all locks once this process is currently not holding any locks. |
| 114 | foreach ( $pathsByTypeByBucket as $bucket => $bucketPathsByType ) { |
| 115 | $status->merge( $this->doUnlockingRequestBucket( $bucket, $bucketPathsByType ) ); |
| 116 | } |
| 117 | if ( $this->locksHeld === [] ) { |
| 118 | $status->merge( $this->releaseAllLocks() ); |
| 119 | $this->degradedBuckets = []; // safe to retry the normal quorum |
| 120 | } |
| 121 | |
| 122 | return $status; |
| 123 | } |
| 124 | |
| 125 | /** |
| 126 | * Attempt to acquire locks with the peers for a bucket. |
| 127 | * This is all or nothing; if any key is locked then this totally fails. |
| 128 | * |
| 129 | * @param int $bucket |
| 130 | * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths |
| 131 | * @return StatusValue |
| 132 | */ |
| 133 | final protected function doLockingRequestBucket( $bucket, array $pathsByType ) { |
| 134 | return $this->collectPledgeQuorum( |
| 135 | $bucket, |
| 136 | function ( $lockSrv ) use ( $pathsByType ) { |
| 137 | return $this->getLocksOnServer( $lockSrv, $pathsByType ); |
| 138 | } |
| 139 | ); |
| 140 | } |
| 141 | |
| 142 | /** |
| 143 | * Attempt to release locks with the peers for a bucket |
| 144 | * |
| 145 | * @param int $bucket |
| 146 | * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths |
| 147 | * @return StatusValue |
| 148 | */ |
| 149 | final protected function doUnlockingRequestBucket( $bucket, array $pathsByType ) { |
| 150 | return $this->releasePledges( |
| 151 | $bucket, |
| 152 | function ( $lockSrv ) use ( $pathsByType ) { |
| 153 | return $this->freeLocksOnServer( $lockSrv, $pathsByType ); |
| 154 | } |
| 155 | ); |
| 156 | } |
| 157 | |
| 158 | /** |
| 159 | * Attempt to acquire pledges with the peers for a bucket. |
| 160 | * This is all or nothing; if any key is already pledged then this totally fails. |
| 161 | * |
| 162 | * @param int $bucket |
| 163 | * @param callable $callback Pledge method taking a server name and yielding a StatusValue |
| 164 | * @return StatusValue |
| 165 | */ |
| 166 | final protected function collectPledgeQuorum( $bucket, callable $callback ) { |
| 167 | $status = StatusValue::newGood(); |
| 168 | |
| 169 | $yesVotes = 0; // locks made on trustable servers |
| 170 | $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers |
| 171 | $quorum = floor( $votesLeft / 2 + 1 ); // simple majority |
| 172 | // Get votes for each peer, in order, until we have enough... |
| 173 | foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) { |
| 174 | if ( !$this->isServerUp( $lockSrv ) ) { |
| 175 | --$votesLeft; |
| 176 | $status->warning( 'lockmanager-fail-svr-acquire', $lockSrv ); |
| 177 | $this->degradedBuckets[$bucket] = time(); |
| 178 | continue; // server down? |
| 179 | } |
| 180 | // Attempt to acquire the lock on this peer |
| 181 | $status->merge( $callback( $lockSrv ) ); |
| 182 | if ( !$status->isOK() ) { |
| 183 | return $status; // vetoed; resource locked |
| 184 | } |
| 185 | ++$yesVotes; // success for this peer |
| 186 | if ( $yesVotes >= $quorum ) { |
| 187 | return $status; // lock obtained |
| 188 | } |
| 189 | --$votesLeft; |
| 190 | $votesNeeded = $quorum - $yesVotes; |
| 191 | if ( $votesNeeded > $votesLeft ) { |
| 192 | break; // short-circuit |
| 193 | } |
| 194 | } |
| 195 | // At this point, we must not have met the quorum |
| 196 | $status->setResult( false ); |
| 197 | |
| 198 | return $status; |
| 199 | } |
| 200 | |
| 201 | /** |
| 202 | * Attempt to release pledges with the peers for a bucket |
| 203 | * |
| 204 | * @param int $bucket |
| 205 | * @param callable $callback Pledge method taking a server name and yielding a StatusValue |
| 206 | * @return StatusValue |
| 207 | */ |
| 208 | final protected function releasePledges( $bucket, callable $callback ) { |
| 209 | $status = StatusValue::newGood(); |
| 210 | |
| 211 | $yesVotes = 0; // locks freed on trustable servers |
| 212 | $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers |
| 213 | $quorum = floor( $votesLeft / 2 + 1 ); // simple majority |
| 214 | $isDegraded = isset( $this->degradedBuckets[$bucket] ); // not the normal quorum? |
| 215 | foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) { |
| 216 | if ( !$this->isServerUp( $lockSrv ) ) { |
| 217 | $status->warning( 'lockmanager-fail-svr-release', $lockSrv ); |
| 218 | } else { |
| 219 | // Attempt to release the lock on this peer |
| 220 | $status->merge( $callback( $lockSrv ) ); |
| 221 | ++$yesVotes; // success for this peer |
| 222 | // Normally the first peers form the quorum, and the others are ignored. |
| 223 | // Ignore them in this case, but not when an alternative quorum was used. |
| 224 | if ( $yesVotes >= $quorum && !$isDegraded ) { |
| 225 | break; // lock released |
| 226 | } |
| 227 | } |
| 228 | } |
| 229 | // Set a bad StatusValue if the quorum was not met. |
| 230 | // Assumes the same "up" servers as during the acquire step. |
| 231 | $status->setResult( $yesVotes >= $quorum ); |
| 232 | |
| 233 | return $status; |
| 234 | } |
| 235 | |
| 236 | /** |
| 237 | * Get the bucket for resource path. |
| 238 | * This should avoid throwing any exceptions. |
| 239 | * |
| 240 | * @param string $path |
| 241 | * @return int |
| 242 | */ |
| 243 | protected function getBucketFromPath( $path ) { |
| 244 | $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits) |
| 245 | return (int)base_convert( $prefix, 16, 10 ) % count( $this->srvsByBucket ); |
| 246 | } |
| 247 | |
| 248 | /** |
| 249 | * Check if a lock server is up. |
| 250 | * This should process cache results to reduce RTT. |
| 251 | * |
| 252 | * @param string $lockSrv |
| 253 | * @return bool |
| 254 | */ |
| 255 | abstract protected function isServerUp( $lockSrv ); |
| 256 | |
| 257 | /** |
| 258 | * Get a connection to a lock server and acquire locks |
| 259 | * |
| 260 | * @param string $lockSrv |
| 261 | * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths |
| 262 | * @return StatusValue |
| 263 | */ |
| 264 | abstract protected function getLocksOnServer( $lockSrv, array $pathsByType ); |
| 265 | |
| 266 | /** |
| 267 | * Get a connection to a lock server and release locks on $paths. |
| 268 | * |
| 269 | * Subclasses must effectively implement this or releaseAllLocks(). |
| 270 | * |
| 271 | * @param string $lockSrv |
| 272 | * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths |
| 273 | * @return StatusValue |
| 274 | */ |
| 275 | abstract protected function freeLocksOnServer( $lockSrv, array $pathsByType ); |
| 276 | |
| 277 | /** |
| 278 | * Release all locks that this session is holding. |
| 279 | * |
| 280 | * Subclasses must effectively implement this or freeLocksOnServer(). |
| 281 | * |
| 282 | * @return StatusValue |
| 283 | */ |
| 284 | abstract protected function releaseAllLocks(); |
| 285 | |
| 286 | final protected function doLock( array $paths, $type ) { |
| 287 | // @phan-suppress-previous-line PhanPluginNeverReturnMethod |
| 288 | throw new LogicException( __METHOD__ . ': proxy class does not need this method.' ); |
| 289 | } |
| 290 | |
| 291 | final protected function doUnlock( array $paths, $type ) { |
| 292 | // @phan-suppress-previous-line PhanPluginNeverReturnMethod |
| 293 | throw new LogicException( __METHOD__ . ': proxy class does not need this method.' ); |
| 294 | } |
| 295 | } |