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Fix NRE in AsyncReaderWriterLock.ReadLock method #2469

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Merged
merged 1 commit into from
Aug 5, 2020
Merged

Fix NRE in AsyncReaderWriterLock.ReadLock method #2469

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12 changes: 7 additions & 5 deletions src/NHibernate/Util/AsyncReaderWriterLock.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -82,23 +82,23 @@ public async Task<Releaser> WriteLockAsync()

public Releaser ReadLock()
{
if (CanEnterReadLock())
if (CanEnterReadLock(out var waitingReadLockSemaphore))
{
return _readerReleaser;
}

_waitingReadLockSemaphore.Wait();
waitingReadLockSemaphore.Wait();

return _readerReleaser;
}

public Task<Releaser> ReadLockAsync()
{
return CanEnterReadLock() ? _readerReleaserTask : ReadLockInternalAsync();
return CanEnterReadLock(out var waitingReadLockSemaphore) ? _readerReleaserTask : ReadLockInternalAsync();

async Task<Releaser> ReadLockInternalAsync()
{
await _waitingReadLockSemaphore.WaitAsync().ConfigureAwait(false);
await waitingReadLockSemaphore.WaitAsync().ConfigureAwait(false);

return _readerReleaser;
}
Expand Down Expand Up @@ -165,14 +165,15 @@ private void ExitWriteLock()
}
}

private bool CanEnterReadLock()
private bool CanEnterReadLock(out SemaphoreSlim waitingReadLockSemaphore)
{
lock (_writeLockSemaphore)
{
AssertNotDisposed();
if (_writersWaiting == 0 && _writeLockSemaphore.CurrentCount > 0)
{
_currentReaders++;
waitingReadLockSemaphore = null;

return true;
}
Expand All @@ -183,6 +184,7 @@ private bool CanEnterReadLock()
}

_readersWaiting++;
waitingReadLockSemaphore = _waitingReadLockSemaphore;

return false;
}
Expand Down