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[13] prevent lock values from going negative with memcache backend #10180

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Merged
MorrisJobke merged 1 commit into from
Jul 11, 2018
Merged

[13] prevent lock values from going negative with memcache backend #10180

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10 changes: 8 additions & 2 deletions lib/private/Lock/MemcacheLockingProvider.php
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Original file line number Diff line number Diff line change
Expand Up @@ -89,14 +89,20 @@ public function acquireLock($path, $type) {
*/
public function releaseLock($path, $type) {
if ($type === self::LOCK_SHARED) {
$newValue = 0;
if ($this->getOwnSharedLockCount($path) === 1) {
$removed = $this->memcache->cad($path, 1); // if we're the only one having a shared lock we can remove it in one go
if (!$removed) { //someone else also has a shared lock, decrease only
$this->memcache->dec($path);
$newValue = $this->memcache->dec($path);
}
} else {
// if we own more than one lock ourselves just decrease
$this->memcache->dec($path);
$newValue = $this->memcache->dec($path);
}

// if we somehow release more locks then exists, reset the lock
if ($newValue < 0) {
$this->memcache->cad($path, $newValue);
}
} else if ($type === self::LOCK_EXCLUSIVE) {
$this->memcache->cad($path, 'exclusive');
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12 changes: 12 additions & 0 deletions tests/lib/Lock/LockingProvider.php
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Original file line number Diff line number Diff line change
Expand Up @@ -243,4 +243,16 @@ public function testChangeLockToSharedFromShared() {
$this->instance->acquireLock('foo', ILockingProvider::LOCK_SHARED);
$this->instance->changeLock('foo', ILockingProvider::LOCK_SHARED);
}

public function testReleaseNonExistingShared() {
$this->instance->acquireLock('foo', ILockingProvider::LOCK_SHARED);
$this->instance->releaseLock('foo', ILockingProvider::LOCK_SHARED);

// releasing a lock once to many should not result in a locked state
$this->instance->releaseLock('foo', ILockingProvider::LOCK_SHARED);

$this->instance->acquireLock('foo', ILockingProvider::LOCK_EXCLUSIVE);
$this->assertTrue($this->instance->isLocked('foo', ILockingProvider::LOCK_EXCLUSIVE));
$this->instance->releaseLock('foo', ILockingProvider::LOCK_EXCLUSIVE);
}
}