MediaWiki  1.28.1
QuorumLockManager.php
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1 <?php
31 abstract class QuorumLockManager extends LockManager {
33  protected $srvsByBucket = []; // (bucket index => (lsrv1, lsrv2, ...))
34 
36  protected $degradedBuckets = []; // (bucket index => UNIX timestamp)
37 
38  final protected function doLock( array $paths, $type ) {
39  return $this->doLockByType( [ $type => $paths ] );
40  }
41 
42  final protected function doUnlock( array $paths, $type ) {
43  return $this->doUnlockByType( [ $type => $paths ] );
44  }
45 
46  protected function doLockByType( array $pathsByType ) {
48 
49  $pathsToLock = []; // (bucket => type => paths)
50  // Get locks that need to be acquired (buckets => locks)...
51  foreach ( $pathsByType as $type => $paths ) {
52  foreach ( $paths as $path ) {
53  if ( isset( $this->locksHeld[$path][$type] ) ) {
54  ++$this->locksHeld[$path][$type];
55  } else {
56  $bucket = $this->getBucketFromPath( $path );
57  $pathsToLock[$bucket][$type][] = $path;
58  }
59  }
60  }
61 
62  $lockedPaths = []; // files locked in this attempt (type => paths)
63  // Attempt to acquire these locks...
64  foreach ( $pathsToLock as $bucket => $pathsToLockByType ) {
65  // Try to acquire the locks for this bucket
66  $status->merge( $this->doLockingRequestBucket( $bucket, $pathsToLockByType ) );
67  if ( !$status->isOK() ) {
68  $status->merge( $this->doUnlockByType( $lockedPaths ) );
69 
70  return $status;
71  }
72  // Record these locks as active
73  foreach ( $pathsToLockByType as $type => $paths ) {
74  foreach ( $paths as $path ) {
75  $this->locksHeld[$path][$type] = 1; // locked
76  // Keep track of what locks were made in this attempt
77  $lockedPaths[$type][] = $path;
78  }
79  }
80  }
81 
82  return $status;
83  }
84 
85  protected function doUnlockByType( array $pathsByType ) {
87 
88  $pathsToUnlock = []; // (bucket => type => paths)
89  foreach ( $pathsByType as $type => $paths ) {
90  foreach ( $paths as $path ) {
91  if ( !isset( $this->locksHeld[$path][$type] ) ) {
92  $status->warning( 'lockmanager-notlocked', $path );
93  } else {
94  --$this->locksHeld[$path][$type];
95  // Reference count the locks held and release locks when zero
96  if ( $this->locksHeld[$path][$type] <= 0 ) {
97  unset( $this->locksHeld[$path][$type] );
98  $bucket = $this->getBucketFromPath( $path );
99  $pathsToUnlock[$bucket][$type][] = $path;
100  }
101  if ( !count( $this->locksHeld[$path] ) ) {
102  unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
103  }
104  }
105  }
106  }
107 
108  // Remove these specific locks if possible, or at least release
109  // all locks once this process is currently not holding any locks.
110  foreach ( $pathsToUnlock as $bucket => $pathsToUnlockByType ) {
111  $status->merge( $this->doUnlockingRequestBucket( $bucket, $pathsToUnlockByType ) );
112  }
113  if ( !count( $this->locksHeld ) ) {
114  $status->merge( $this->releaseAllLocks() );
115  $this->degradedBuckets = []; // safe to retry the normal quorum
116  }
117 
118  return $status;
119  }
120 
129  final protected function doLockingRequestBucket( $bucket, array $pathsByType ) {
131 
132  $yesVotes = 0; // locks made on trustable servers
133  $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
134  $quorum = floor( $votesLeft / 2 + 1 ); // simple majority
135  // Get votes for each peer, in order, until we have enough...
136  foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) {
137  if ( !$this->isServerUp( $lockSrv ) ) {
138  --$votesLeft;
139  $status->warning( 'lockmanager-fail-svr-acquire', $lockSrv );
140  $this->degradedBuckets[$bucket] = time();
141  continue; // server down?
142  }
143  // Attempt to acquire the lock on this peer
144  $status->merge( $this->getLocksOnServer( $lockSrv, $pathsByType ) );
145  if ( !$status->isOK() ) {
146  return $status; // vetoed; resource locked
147  }
148  ++$yesVotes; // success for this peer
149  if ( $yesVotes >= $quorum ) {
150  return $status; // lock obtained
151  }
152  --$votesLeft;
153  $votesNeeded = $quorum - $yesVotes;
154  if ( $votesNeeded > $votesLeft ) {
155  break; // short-circuit
156  }
157  }
158  // At this point, we must not have met the quorum
159  $status->setResult( false );
160 
161  return $status;
162  }
163 
171  final protected function doUnlockingRequestBucket( $bucket, array $pathsByType ) {
173 
174  $yesVotes = 0; // locks freed on trustable servers
175  $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
176  $quorum = floor( $votesLeft / 2 + 1 ); // simple majority
177  $isDegraded = isset( $this->degradedBuckets[$bucket] ); // not the normal quorum?
178  foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) {
179  if ( !$this->isServerUp( $lockSrv ) ) {
180  $status->warning( 'lockmanager-fail-svr-release', $lockSrv );
181  } else {
182  // Attempt to release the lock on this peer
183  $status->merge( $this->freeLocksOnServer( $lockSrv, $pathsByType ) );
184  ++$yesVotes; // success for this peer
185  // Normally the first peers form the quorum, and the others are ignored.
186  // Ignore them in this case, but not when an alternative quorum was used.
187  if ( $yesVotes >= $quorum && !$isDegraded ) {
188  break; // lock released
189  }
190  }
191  }
192  // Set a bad StatusValue if the quorum was not met.
193  // Assumes the same "up" servers as during the acquire step.
194  $status->setResult( $yesVotes >= $quorum );
195 
196  return $status;
197  }
198 
206  protected function getBucketFromPath( $path ) {
207  $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
208  return (int)base_convert( $prefix, 16, 10 ) % count( $this->srvsByBucket );
209  }
210 
218  abstract protected function isServerUp( $lockSrv );
219 
227  abstract protected function getLocksOnServer( $lockSrv, array $pathsByType );
228 
238  abstract protected function freeLocksOnServer( $lockSrv, array $pathsByType );
239 
247  abstract protected function releaseAllLocks();
248 }
the array() calling protocol came about after MediaWiki 1.4rc1.
getLocksOnServer($lockSrv, array $pathsByType)
Get a connection to a lock server and acquire locks.
releaseAllLocks()
Release all locks that this session is holding.
array $srvsByBucket
Map of bucket indexes to peer server lists.
getBucketFromPath($path)
Get the bucket for resource path.
array $degradedBuckets
Map of degraded buckets.
doUnlockByType(array $pathsByType)
doUnlockingRequestBucket($bucket, array $pathsByType)
Attempt to release locks with the peers for a bucket.
freeLocksOnServer($lockSrv, array $pathsByType)
Get a connection to a lock server and release locks on $paths.
doUnlock(array $paths, $type)
isServerUp($lockSrv)
Check if a lock server is up.
static newGood($value=null)
Factory function for good results.
Definition: StatusValue.php:76
doLock(array $paths, $type)
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Definition: distributors.txt:9
doLockByType(array $pathsByType)
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Definition: injection.txt:35
Class for handling resource locking.
Definition: LockManager.php:47
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Definition: hooks.txt:1046
Version of LockManager that uses a quorum from peer servers for locks.
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Definition: hooks.txt:2491
doLockingRequestBucket($bucket, array $pathsByType)
Attempt to acquire locks with the peers for a bucket.