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prevent lock values from going negative with memcache backend 

This can be caused by the code releasing more locks then it acquires,
once the lock value becomes negative it's likely that it will never be able
to change into an exclusive lock again.

Signed-off-by: Robin Appelman <robin@icewind.nl>
This commit is contained in:
Robin Appelman 2018-07-05 14:39:10 +02:00
parent 42912a0e25
commit 3d5acbb1d0
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GPG Key ID: 42B69D8A64526EFB
2 changed files with 20 additions and 2 deletions
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10
lib/private/Lock/MemcacheLockingProvider.php
View File

@ -90,14 +90,20 @@ class MemcacheLockingProvider extends AbstractLockingProvider {
*/
public function releaseLock(string $path, int $type) {
if ($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');

12
tests/lib/Lock/LockingProvider.php
View File

@ -243,4 +243,16 @@ abstract class LockingProvider extends TestCase {
$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);
}
}