HDDS-12356. OM Gatekeeper Prototype #5
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szetszwo
reviewed
Apr 4, 2025
| */ | ||
| public final class LockInfo implements Comparable<LockInfo> { | ||
| private final String key; | ||
| private final boolean isWriteLock; |
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Use an enum is better than a boolean; see "Never Use Booleans for Something That Has Two States Now, but Might Have More Later".
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| public AutoCloseable lock(OmLockInfo lockInfo) throws InterruptedException, TimeoutException { | ||
| // Common case is 1 volume, 1 bucket, and at most 2 key locks. | ||
| List<Lock> locks = new ArrayList<>(4); | ||
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| Optional<LockInfo> optionalVolumeLock = lockInfo.getVolumeLock(); | ||
| Optional<LockInfo> optionalBucketLock = lockInfo.getBucketLock(); | ||
| Optional<Set<LockInfo>> optionalKeyLocks = lockInfo.getKeyLocks(); | ||
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| if (optionalVolumeLock.isPresent()) { | ||
| LockInfo volumeLockInfo = optionalVolumeLock.get(); | ||
| if (volumeLockInfo.isWriteLock()) { | ||
| locks.add(volumeLocks.get(volumeLockInfo.getKey()).writeLock()); | ||
| } else { | ||
| locks.add(volumeLocks.get(volumeLockInfo.getKey()).readLock()); | ||
| } | ||
| } | ||
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| if (optionalBucketLock.isPresent()) { | ||
| LockInfo bucketLockInfo = optionalBucketLock.get(); | ||
| if (bucketLockInfo.isWriteLock()) { | ||
| locks.add(bucketLocks.get(bucketLockInfo.getKey()).writeLock()); | ||
| } else { | ||
| locks.add(bucketLocks.get(bucketLockInfo.getKey()).readLock()); | ||
| } | ||
| } | ||
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| if (optionalKeyLocks.isPresent()) { | ||
| for (Lock keyLock: keyLocks.bulkGet(optionalKeyLocks.get())) { | ||
| locks.add(keyLock); | ||
| } | ||
| } | ||
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| acquireLocks(locks); | ||
| return () -> releaseLocks(locks); | ||
| } |
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The lock overhead probably is quite high in this method.
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| @Override | ||
| public int compareTo(@NotNull LockInfo other) { | ||
| return Integer.compare(hashCode(), other.hashCode()); |
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Sort by hashCode won't work with guava Striped. For example
- the number of stripe: 1024.
- hash code A = 1
- hash code B = 1025.
compareTo will return non-zero but they are mapped to the same lock.
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| private final LockInfo volumeLock; | ||
| private final LockInfo bucketLock; | ||
| private final Set<LockInfo> keyLocks; |
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If we require locking on two or more volumes/buckets later on, it will require a lot of code change.
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| private void acquireLocks(List<Lock> locks) throws TimeoutException, InterruptedException { | ||
| List<Lock> acquiredLocks = new ArrayList<>(locks.size()); | ||
| for (Lock lock: locks) { | ||
| if (lock.tryLock(timeoutMillis, TimeUnit.MILLISECONDS)) { | ||
| try { | ||
| acquiredLocks.add(lock); | ||
| } catch (Throwable e) { | ||
| // We acquired this lock but were unable to add it to our acquired locks list. | ||
| lock.unlock(); | ||
| releaseLocks(acquiredLocks); | ||
| throw e; | ||
| } | ||
| } else { | ||
| releaseLocks(acquiredLocks); | ||
| throw new TimeoutException("Failed to acquire lock after the given timeout."); | ||
| } | ||
| } | ||
| } |
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Concurrently, if the lock.tryLock(..) is interrupted, the partial lock won't be released. Getting everything right with timeout is not easy.
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What changes were proposed in this pull request?
Prototype for the granular locking framework OBS implementation. The following aspects are considered in this design:
OmLockInfowill be consumed by all of the ~100 OM requests, so it should be as minimal as possible.OmRequestGatekeeperprovides one public method with a simple contract, and an initial implementation that is as simple as possible.Since this is prototype/demonstration code, see inline for comments on how the pieces will fit together.
What is the link to the Apache JIRA
HDDS-12356
How was this patch tested?
N/A, for demonstration and discussion only.