Prevent parallel file lock clear #3714
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...ne/src/main/java/com/apple/foundationdb/record/lucene/directory/FDBDirectoryLockFactory.java
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ScottDugas
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...ne/src/main/java/com/apple/foundationdb/record/lucene/directory/FDBDirectoryLockFactory.java
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| private void fileLockClearFlushAndClose(boolean isRecovery) { | ||
| synchronized (clearingLockNowLock) { | ||
| // Here: this function is being called from too many paths. Until cleanup, this guard is here to avoid recursions |
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If indeed all that the synchronized block is trying to do is protect a boolean, then an AtomicBoolean can do the job. It seems as if we are not trying to create a totally exclusive code flow but just prevent "too many" runs of the same methods, right?
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Changed to AtomicBoolean.
The code supposed to prevent concurrent lock clears, which seems to be caused by concurrent, possibly recursive, calls to directory close.
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Had to undo the AtomicBoolean use as some tests were failing.
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I'm curious: Which tests failed?
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Not sure, but it might have been testMultiClose.
...ne/src/main/java/com/apple/foundationdb/record/lucene/directory/FDBDirectoryLockFactory.java
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FDBDirectory: When file lock clear is called in parallel by multiple threads, synchronically waiting for the first thread's clear to complete seems to be a better strategy. Resolves FoundationDB#3713
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| closed = flushed; // allow close retry | ||
| closingContext = null; | ||
| synchronized (clearingLockNowLock) { | ||
| // clearing under lock to avoid spotbugsMain's "Inconsistent synchronization" issue. |
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Should this be in a finally around all the code above?
i.e. what happens if the asyncToSync calls above fail?
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Good point!
I've moved it to a fileLockFunc's whenComplete step.
| private void fileLockClearFlushAndClose(boolean isRecovery) { | ||
| synchronized (clearingLockNowLock) { | ||
| // Here: this function is being called from too many paths. Until cleanup, this guard is here to avoid recursions | ||
| if (clearingLockNow) { |
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I've only seen it for lazy instantiation, but would it be worth to duplicate this before the synchronized lock to avoid entering the Synchronized lock if already clearing?
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I can either do that or remove the synchronized lock altogether (since our concern is recursion, the synchronized lock might be an overkill...)
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| private void fileLockClearFlushAndClose(boolean isRecovery) { |
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It sounds like there are some concurrency challenges with FDBDirectoryLock, it would probably be good to add some tests that try to clear this lock concurrently.
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FDBDirectory: When file lock clear is called in parallel by multiple threads, synchronically waiting for the first thread's clear to complete seems to be a better strategy.
Resolves #3713