--- /dev/null
+<?php
+/**
+ * Version of LockManager that uses a quorum from peer servers for locks.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ * @ingroup LockManager
+ */
+
+/**
+ * Version of LockManager that uses a quorum from peer servers for locks.
+ * The resource space can also be sharded into separate peer groups.
+ *
+ * @ingroup LockManager
+ * @since 1.20
+ */
+abstract class QuorumLockManager extends LockManager {
+ /** @var array Map of bucket indexes to peer server lists */
+ protected $srvsByBucket = []; // (bucket index => (lsrv1, lsrv2, ...))
+
+ /** @var array Map of degraded buckets */
+ protected $degradedBuckets = []; // (bucket index => UNIX timestamp)
+
+ final protected function doLock( array $paths, $type ) {
+ return $this->doLockByType( [ $type => $paths ] );
+ }
+
+ final protected function doUnlock( array $paths, $type ) {
+ return $this->doUnlockByType( [ $type => $paths ] );
+ }
+
+ protected function doLockByType( array $pathsByType ) {
+ $status = StatusValue::newGood();
+
+ $pathsToLock = []; // (bucket => type => paths)
+ // Get locks that need to be acquired (buckets => locks)...
+ foreach ( $pathsByType as $type => $paths ) {
+ foreach ( $paths as $path ) {
+ if ( isset( $this->locksHeld[$path][$type] ) ) {
+ ++$this->locksHeld[$path][$type];
+ } else {
+ $bucket = $this->getBucketFromPath( $path );
+ $pathsToLock[$bucket][$type][] = $path;
+ }
+ }
+ }
+
+ $lockedPaths = []; // files locked in this attempt (type => paths)
+ // Attempt to acquire these locks...
+ foreach ( $pathsToLock as $bucket => $pathsToLockByType ) {
+ // Try to acquire the locks for this bucket
+ $status->merge( $this->doLockingRequestBucket( $bucket, $pathsToLockByType ) );
+ if ( !$status->isOK() ) {
+ $status->merge( $this->doUnlockByType( $lockedPaths ) );
+
+ return $status;
+ }
+ // Record these locks as active
+ foreach ( $pathsToLockByType as $type => $paths ) {
+ foreach ( $paths as $path ) {
+ $this->locksHeld[$path][$type] = 1; // locked
+ // Keep track of what locks were made in this attempt
+ $lockedPaths[$type][] = $path;
+ }
+ }
+ }
+
+ return $status;
+ }
+
+ protected function doUnlockByType( array $pathsByType ) {
+ $status = StatusValue::newGood();
+
+ $pathsToUnlock = []; // (bucket => type => paths)
+ foreach ( $pathsByType as $type => $paths ) {
+ foreach ( $paths as $path ) {
+ if ( !isset( $this->locksHeld[$path][$type] ) ) {
+ $status->warning( 'lockmanager-notlocked', $path );
+ } else {
+ --$this->locksHeld[$path][$type];
+ // Reference count the locks held and release locks when zero
+ if ( $this->locksHeld[$path][$type] <= 0 ) {
+ unset( $this->locksHeld[$path][$type] );
+ $bucket = $this->getBucketFromPath( $path );
+ $pathsToUnlock[$bucket][$type][] = $path;
+ }
+ if ( !count( $this->locksHeld[$path] ) ) {
+ unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
+ }
+ }
+ }
+ }
+
+ // Remove these specific locks if possible, or at least release
+ // all locks once this process is currently not holding any locks.
+ foreach ( $pathsToUnlock as $bucket => $pathsToUnlockByType ) {
+ $status->merge( $this->doUnlockingRequestBucket( $bucket, $pathsToUnlockByType ) );
+ }
+ if ( !count( $this->locksHeld ) ) {
+ $status->merge( $this->releaseAllLocks() );
+ $this->degradedBuckets = []; // safe to retry the normal quorum
+ }
+
+ return $status;
+ }
+
+ /**
+ * Attempt to acquire locks with the peers for a bucket.
+ * This is all or nothing; if any key is locked then this totally fails.
+ *
+ * @param int $bucket
+ * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+ * @return StatusValue
+ */
+ final protected function doLockingRequestBucket( $bucket, array $pathsByType ) {
+ return $this->collectPledgeQuorum(
+ $bucket,
+ function ( $lockSrv ) use ( $pathsByType ) {
+ return $this->getLocksOnServer( $lockSrv, $pathsByType );
+ }
+ );
+ }
+
+ /**
+ * Attempt to release locks with the peers for a bucket
+ *
+ * @param int $bucket
+ * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+ * @return StatusValue
+ */
+ final protected function doUnlockingRequestBucket( $bucket, array $pathsByType ) {
+ return $this->releasePledges(
+ $bucket,
+ function ( $lockSrv ) use ( $pathsByType ) {
+ return $this->freeLocksOnServer( $lockSrv, $pathsByType );
+ }
+ );
+ }
+
+ /**
+ * Attempt to acquire pledges with the peers for a bucket.
+ * This is all or nothing; if any key is already pledged then this totally fails.
+ *
+ * @param int $bucket
+ * @param callable $callback Pledge method taking a server name and yeilding a StatusValue
+ * @return StatusValue
+ */
+ final protected function collectPledgeQuorum( $bucket, callable $callback ) {
+ $status = StatusValue::newGood();
+
+ $yesVotes = 0; // locks made on trustable servers
+ $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
+ $quorum = floor( $votesLeft / 2 + 1 ); // simple majority
+ // Get votes for each peer, in order, until we have enough...
+ foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) {
+ if ( !$this->isServerUp( $lockSrv ) ) {
+ --$votesLeft;
+ $status->warning( 'lockmanager-fail-svr-acquire', $lockSrv );
+ $this->degradedBuckets[$bucket] = time();
+ continue; // server down?
+ }
+ // Attempt to acquire the lock on this peer
+ $status->merge( $callback( $lockSrv ) );
+ if ( !$status->isOK() ) {
+ return $status; // vetoed; resource locked
+ }
+ ++$yesVotes; // success for this peer
+ if ( $yesVotes >= $quorum ) {
+ return $status; // lock obtained
+ }
+ --$votesLeft;
+ $votesNeeded = $quorum - $yesVotes;
+ if ( $votesNeeded > $votesLeft ) {
+ break; // short-circuit
+ }
+ }
+ // At this point, we must not have met the quorum
+ $status->setResult( false );
+
+ return $status;
+ }
+
+ /**
+ * Attempt to release pledges with the peers for a bucket
+ *
+ * @param int $bucket
+ * @param callable $callback Pledge method taking a server name and yeilding a StatusValue
+ * @return StatusValue
+ */
+ final protected function releasePledges( $bucket, callable $callback ) {
+ $status = StatusValue::newGood();
+
+ $yesVotes = 0; // locks freed on trustable servers
+ $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
+ $quorum = floor( $votesLeft / 2 + 1 ); // simple majority
+ $isDegraded = isset( $this->degradedBuckets[$bucket] ); // not the normal quorum?
+ foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) {
+ if ( !$this->isServerUp( $lockSrv ) ) {
+ $status->warning( 'lockmanager-fail-svr-release', $lockSrv );
+ } else {
+ // Attempt to release the lock on this peer
+ $status->merge( $callback( $lockSrv ) );
+ ++$yesVotes; // success for this peer
+ // Normally the first peers form the quorum, and the others are ignored.
+ // Ignore them in this case, but not when an alternative quorum was used.
+ if ( $yesVotes >= $quorum && !$isDegraded ) {
+ break; // lock released
+ }
+ }
+ }
+ // Set a bad StatusValue if the quorum was not met.
+ // Assumes the same "up" servers as during the acquire step.
+ $status->setResult( $yesVotes >= $quorum );
+
+ return $status;
+ }
+
+ /**
+ * Get the bucket for resource path.
+ * This should avoid throwing any exceptions.
+ *
+ * @param string $path
+ * @return int
+ */
+ protected function getBucketFromPath( $path ) {
+ $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
+ return (int)base_convert( $prefix, 16, 10 ) % count( $this->srvsByBucket );
+ }
+
+ /**
+ * Check if a lock server is up.
+ * This should process cache results to reduce RTT.
+ *
+ * @param string $lockSrv
+ * @return bool
+ */
+ abstract protected function isServerUp( $lockSrv );
+
+ /**
+ * Get a connection to a lock server and acquire locks
+ *
+ * @param string $lockSrv
+ * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+ * @return StatusValue
+ */
+ abstract protected function getLocksOnServer( $lockSrv, array $pathsByType );
+
+ /**
+ * Get a connection to a lock server and release locks on $paths.
+ *
+ * Subclasses must effectively implement this or releaseAllLocks().
+ *
+ * @param string $lockSrv
+ * @param array $pathsByType Map of LockManager::LOCK_* constants to lists of paths
+ * @return StatusValue
+ */
+ abstract protected function freeLocksOnServer( $lockSrv, array $pathsByType );
+
+ /**
+ * Release all locks that this session is holding.
+ *
+ * Subclasses must effectively implement this or freeLocksOnServer().
+ *
+ * @return StatusValue
+ */
+ abstract protected function releaseAllLocks();
+}
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