public ValueTask DisposeAsync()
{
if (_objAsyncLock._intDisposedStatus > 1)
{
throw new ObjectDisposedException(nameof(_objAsyncLock));
}
DebuggableSemaphoreSlim objNextSemaphoreSlim = _objAsyncLock._objCurrentSemaphore.Value;
if (_objNextSemaphore != objNextSemaphoreSlim)
{
if (objNextSemaphoreSlim == _objCurrentSemaphore)
{
throw new InvalidOperationException(
"_objNextSemaphore was expected to be the current semaphore. Instead, the old semaphore was never unset.");
}
if (objNextSemaphoreSlim == null)
{
throw new InvalidOperationException(
"_objNextSemaphore was expected to be the current semaphore. Instead, the current semaphore is null.\n\n"
+ "This may be because AsyncLocal's control flow is the inverse of what one expects, so acquiring "
+ "the lock inside a function and then leaving the function before exiting the lock can produce this situation.");
}
throw new InvalidOperationException("_objNextSemaphore was expected to be the current semaphore");
}
// Update _objAsyncLock._objCurrentSemaphore in the calling ExecutionContext
// and defer any awaits to DisposeCoreAsync(). If this isn't done, the
// update will happen in a copy of the ExecutionContext and the caller
// won't see the changes.
_objAsyncLock._objCurrentSemaphore.Value = _objCurrentSemaphore;
return(DisposeCoreAsync());
}
private async Task <IAsyncDisposable> TakeWriteLockCoreAsync(DebuggableSemaphoreSlim objCurrentSemaphore, SafeWriterSemaphoreRelease objRelease, CancellationToken token)
{
try
{
await objCurrentSemaphore.WaitAsync(token);
if (Interlocked.Increment(ref _intCountActiveReaders) == 1)
{
try
{
// Wait for the reader lock only if there have been no other write locks before us
if (_objTopLevelWriterSemaphore.CurrentCount != 0 || objCurrentSemaphore == _objTopLevelWriterSemaphore)
{
await _objReaderSemaphore.WaitAsync(token);
}
}
catch
{
Interlocked.Decrement(ref _intCountActiveReaders);
throw;
}
}
}
catch (OperationCanceledException)
{
//swallow this because it must be handled as a disposal in the original ExecutionContext
}
return(objRelease);
}
public SafeWriterSemaphoreRelease(DebuggableSemaphoreSlim objLastSemaphore, DebuggableSemaphoreSlim objCurrentSemaphore, DebuggableSemaphoreSlim objNextSemaphore, AsyncFriendlyReaderWriterLock objReaderWriterLock)
{
if (objCurrentSemaphore == null)
{
throw new ArgumentNullException(nameof(objCurrentSemaphore));
}
if (objNextSemaphore == null)
{
throw new ArgumentNullException(nameof(objNextSemaphore));
}
if (objLastSemaphore == objCurrentSemaphore)
{
throw new InvalidOperationException(
"Last and current semaphores are identical, this should not happen.");
}
if (objCurrentSemaphore == objNextSemaphore)
{
throw new InvalidOperationException(
"Current and next semaphores are identical, this should not happen.");
}
if (objLastSemaphore == objNextSemaphore)
{
throw new InvalidOperationException(
"Last and next semaphores are identical, this should not happen.");
}
_objLastSemaphore = objLastSemaphore;
_objCurrentSemaphore = objCurrentSemaphore;
_objNextSemaphore = objNextSemaphore;
_objReaderWriterLock = objReaderWriterLock;
}
private static async Task <IAsyncDisposable> TakeLockCoreAsync(DebuggableSemaphoreSlim objCurrentSemaphore, SafeSemaphoreRelease objRelease, CancellationToken token)
{
try
{
await objCurrentSemaphore.WaitAsync(token);
}
catch (OperationCanceledException)
{
//swallow this because it must be handled as a disposal in the original ExecutionContext
}
return(objRelease);
}
public Task <IAsyncDisposable> TakeLockAsync()
{
if (_intDisposedStatus != 0)
{
return(Task.FromException <IAsyncDisposable>(new ObjectDisposedException(nameof(AsyncLock))));
}
DebuggableSemaphoreSlim objNextSemaphore = Utils.SemaphorePool.Get();
DebuggableSemaphoreSlim objCurrentSemaphore = _objCurrentSemaphore.Value ?? _objTopLevelSemaphore;
_objCurrentSemaphore.Value = objNextSemaphore;
SafeSemaphoreRelease objRelease = new SafeSemaphoreRelease(objCurrentSemaphore, objNextSemaphore, this);
return(TakeLockCoreAsync(objCurrentSemaphore, objRelease));
}
/// <summary>
/// Try to asynchronously obtain a lock for reading.
/// </summary>
public Task EnterReadLockAsync(CancellationToken token = default)
{
if (_intDisposedStatus != 0)
{
return(Task.FromException(new ObjectDisposedException(nameof(AsyncFriendlyReaderWriterLock))));
}
token.ThrowIfCancellationRequested();
if (_objTopLevelWriterSemaphore.CurrentCount != 0)
{
return(TakeReadLockCoreLightAsync(token));
}
DebuggableSemaphoreSlim objCurrentSemaphore = _objCurrentWriterSemaphore.Value?.Item2 ?? _objTopLevelWriterSemaphore;
return(TakeReadLockCoreAsync(objCurrentSemaphore, token));
}
/// <summary>
/// Try to synchronously obtain a lock for reading.
/// </summary>
public void EnterReadLock(CancellationToken token = default)
{
if (_intDisposedStatus != 0)
{
throw new ObjectDisposedException(nameof(AsyncFriendlyReaderWriterLock));
}
token.ThrowIfCancellationRequested();
// Only do the complicated steps if any write lock is currently being held, otherwise skip it and just process the read lock
if (_objTopLevelWriterSemaphore.CurrentCount == 0)
{
// Temporarily acquiring a write lock just to mess with the read locks is a bottleneck, so don't do any such setting unless we need it
DebuggableSemaphoreSlim objCurrentSemaphore = _objCurrentWriterSemaphore.Value?.Item2 ?? _objTopLevelWriterSemaphore;
objCurrentSemaphore.SafeWait(token);
try
{
if (Interlocked.Increment(ref _intCountActiveReaders) == 1)
{
try
{
_objReaderSemaphore.SafeWait(token);
}
catch
{
Interlocked.Decrement(ref _intCountActiveReaders);
throw;
}
}
}
finally
{
objCurrentSemaphore.Release();
}
}
else if (Interlocked.Increment(ref _intCountActiveReaders) == 1)
{
try
{
_objReaderSemaphore.SafeWait(token);
}
catch
{
Interlocked.Decrement(ref _intCountActiveReaders);
throw;
}
}
}
public void Dispose()
{
if (_objAsyncLock._intDisposedStatus > 1)
{
throw new ObjectDisposedException(nameof(_objAsyncLock));
}
DebuggableSemaphoreSlim objNextSemaphoreSlim = _objAsyncLock._objCurrentSemaphore.Value;
if (_objNextSemaphore != objNextSemaphoreSlim)
{
if (objNextSemaphoreSlim == _objCurrentSemaphore)
{
throw new InvalidOperationException(
"_objNextSemaphore was expected to be the current semaphore. Instead, the old semaphore was never unset.");
}
if (objNextSemaphoreSlim == null)
{
throw new InvalidOperationException(
"_objNextSemaphore was expected to be the current semaphore. Instead, the current semaphore is null.\n\n"
+ "This may be because AsyncLocal's control flow is the inverse of what one expects, so acquiring "
+ "the lock inside a function and then leaving the function before exiting the lock can produce this situation.");
}
throw new InvalidOperationException("_objNextSemaphore was expected to be the current semaphore");
}
_objAsyncLock._objCurrentSemaphore.Value = _objCurrentSemaphore;
try
{
if (_objCurrentSemaphore.CurrentCount == 0)
{
_objNextSemaphore.SafeWait();
try
{
_objCurrentSemaphore.Release();
}
finally
{
_objNextSemaphore.Release();
}
}
}
finally
{
Utils.SemaphorePool.Return(ref _objNextSemaphore);
}
}
private async Task <IAsyncDisposable> TakeWriteLockCoreAsync(DebuggableSemaphoreSlim objCurrentSemaphore, SafeWriterSemaphoreRelease objRelease)
{
await objCurrentSemaphore.WaitAsync();
if (Interlocked.Increment(ref _intCountActiveReaders) == 1)
{
try
{
// Wait for the reader lock only if there have been no other write locks before us
if (_objTopLevelWriterSemaphore.CurrentCount != 0 || objCurrentSemaphore == _objTopLevelWriterSemaphore)
{
await _objReaderSemaphore.WaitAsync();
}
}
catch
{
Interlocked.Decrement(ref _intCountActiveReaders);
throw;
}
}
return(objRelease);
}
/// <summary>
/// Try to asynchronously obtain a lock for writing.
/// The returned SafeSemaphoreWriterRelease must be stored for when the write lock is to be released.
/// </summary>
public Task <IAsyncDisposable> EnterWriteLockAsync()
{
if (_intDisposedStatus != 0)
{
return(Task.FromException <IAsyncDisposable>(new ObjectDisposedException(nameof(AsyncFriendlyReaderWriterLock))));
}
(DebuggableSemaphoreSlim objLastSemaphore, DebuggableSemaphoreSlim objCurrentSemaphore)
= _objCurrentWriterSemaphore.Value
?? new Tuple <DebuggableSemaphoreSlim, DebuggableSemaphoreSlim>(null, _objTopLevelWriterSemaphore);
DebuggableSemaphoreSlim objNextSemaphore = Utils.SemaphorePool.Get();
// Extremely hacky solution to buggy semaphore (re)cycling in AsyncLocal
// TODO: Fix this properly. The problem is that after an AsyncLocal shallow-copy in a different context, the semaphores can get returned in the copy without altering the original AsyncLocal
while (objNextSemaphore == objCurrentSemaphore || objNextSemaphore == objLastSemaphore)
{
objNextSemaphore = Utils.SemaphorePool.Get();
}
_objCurrentWriterSemaphore.Value = new Tuple <DebuggableSemaphoreSlim, DebuggableSemaphoreSlim>(objCurrentSemaphore, objNextSemaphore);
SafeWriterSemaphoreRelease objRelease = new SafeWriterSemaphoreRelease(objLastSemaphore, objCurrentSemaphore, objNextSemaphore, this);
return(TakeWriteLockCoreAsync(objCurrentSemaphore, objRelease));
}
public IDisposable TakeLock(CancellationToken token = default)
{
if (_intDisposedStatus != 0)
{
throw new ObjectDisposedException(nameof(AsyncLock));
}
token.ThrowIfCancellationRequested();
DebuggableSemaphoreSlim objNextSemaphore = Utils.SemaphorePool.Get();
DebuggableSemaphoreSlim objCurrentSemaphore = _objCurrentSemaphore.Value ?? _objTopLevelSemaphore;
_objCurrentSemaphore.Value = objNextSemaphore;
try
{
objCurrentSemaphore.SafeWait(token);
}
catch
{
_objCurrentSemaphore.Value = objCurrentSemaphore;
Utils.SemaphorePool.Return(ref objNextSemaphore);
throw;
}
return(new SafeSemaphoreRelease(objCurrentSemaphore, objNextSemaphore, this));
}
/// <summary>
/// Heavier read lock entrant, used if a write lock is already being held somewhere
/// </summary>
private async Task TakeReadLockCoreAsync(DebuggableSemaphoreSlim objCurrentSemaphore, CancellationToken token = default)
{
await objCurrentSemaphore.WaitAsync(token);
try
{
if (Interlocked.Increment(ref _intCountActiveReaders) == 1)
{
try
{
await _objReaderSemaphore.WaitAsync(token);
}
catch
{
Interlocked.Decrement(ref _intCountActiveReaders);
throw;
}
}
}
finally
{
objCurrentSemaphore.Release();
}
}
private static async Task <IAsyncDisposable> TakeLockCoreAsync(DebuggableSemaphoreSlim objCurrentSemaphore, SafeSemaphoreRelease objRelease)
{
await objCurrentSemaphore.WaitAsync();
return(objRelease);
}
public SafeSemaphoreRelease(DebuggableSemaphoreSlim objCurrentSemaphore, DebuggableSemaphoreSlim objNextSemaphore, AsyncLock objAsyncLock)
{
_objCurrentSemaphore = objCurrentSemaphore;
_objNextSemaphore = objNextSemaphore;
_objAsyncLock = objAsyncLock;
}
/// <summary>
/// Try to synchronously obtain a lock for writing.
/// The returned SafeSemaphoreWriterRelease must be stored for when the write lock is to be released.
/// </summary>
public IDisposable EnterWriteLock(CancellationToken token = default)
{
if (_intDisposedStatus != 0)
{
throw new ObjectDisposedException(nameof(AsyncFriendlyReaderWriterLock));
}
token.ThrowIfCancellationRequested();
(DebuggableSemaphoreSlim objLastSemaphore, DebuggableSemaphoreSlim objCurrentSemaphore)
= _objCurrentWriterSemaphore.Value
?? new Tuple <DebuggableSemaphoreSlim, DebuggableSemaphoreSlim>(null, _objTopLevelWriterSemaphore);
DebuggableSemaphoreSlim objNextSemaphore = Utils.SemaphorePool.Get();
// Extremely hacky solution to buggy semaphore (re)cycling in AsyncLocal
// TODO: Fix this properly. The problem is that after an AsyncLocal shallow-copy in a different context, the semaphores can get returned in the copy without altering the original AsyncLocal
while (objNextSemaphore == objCurrentSemaphore || objNextSemaphore == objLastSemaphore)
{
objNextSemaphore = Utils.SemaphorePool.Get();
}
_objCurrentWriterSemaphore.Value = new Tuple <DebuggableSemaphoreSlim, DebuggableSemaphoreSlim>(objCurrentSemaphore, objNextSemaphore);
SafeWriterSemaphoreRelease objRelease = new SafeWriterSemaphoreRelease(objLastSemaphore, objCurrentSemaphore, objNextSemaphore, this);
try
{
objCurrentSemaphore.SafeWait(token);
}
catch
{
_objCurrentWriterSemaphore.Value = new Tuple <DebuggableSemaphoreSlim, DebuggableSemaphoreSlim>(objLastSemaphore, objCurrentSemaphore);
Utils.SemaphorePool.Return(ref objNextSemaphore);
throw;
}
try
{
if (Interlocked.Increment(ref _intCountActiveReaders) == 1)
{
try
{
// Wait for the reader lock only if there have been no other write locks before us
if (_objTopLevelWriterSemaphore.CurrentCount != 0 || objCurrentSemaphore == _objTopLevelWriterSemaphore)
{
_objReaderSemaphore.SafeWait(token);
}
}
catch
{
Interlocked.Decrement(ref _intCountActiveReaders);
throw;
}
}
}
catch
{
_objCurrentWriterSemaphore.Value = new Tuple <DebuggableSemaphoreSlim, DebuggableSemaphoreSlim>(objLastSemaphore, objCurrentSemaphore);
try
{
// ReSharper disable once MethodSupportsCancellation
objNextSemaphore.SafeWait();
try
{
objCurrentSemaphore.Release();
}
finally
{
objNextSemaphore.Release();
}
}
finally
{
Utils.SemaphorePool.Return(ref objNextSemaphore);
}
throw;
}
return(objRelease);
}
