public override ValueTask <bool> WaitToReadAsync(CancellationToken cancellationToken) { // Outside of the lock, check if there are any items waiting to be read. If there are, we're done. if (cancellationToken.IsCancellationRequested) { return(new ValueTask <bool>(Task.FromCanceled <bool>(cancellationToken))); } if (!_parent._items.IsEmpty) { return(new ValueTask <bool>(true)); } SingleConsumerUnboundedChannel <T> parent = _parent; AsyncOperation <bool> oldWaitingReader = null, newWaitingReader; lock (parent.SyncObj) { // Again while holding the lock, check to see if there are any items available. if (!parent._items.IsEmpty) { return(new ValueTask <bool>(true)); } // There aren't any items; if we're done writing, there never will be more items. if (parent._doneWriting != null) { return(parent._doneWriting != ChannelUtilities.s_doneWritingSentinel ? new ValueTask <bool>(Task.FromException <bool>(parent._doneWriting)) : new ValueTask <bool>(false)); } // Try to use the singleton waiter. If it's currently being used, then the channel // is being used erroneously, and we cancel the outstanding operation. oldWaitingReader = parent._waitingReader; if (!cancellationToken.CanBeCanceled && _waiterSingleton.TryOwnAndReset()) { newWaitingReader = _waiterSingleton; if (newWaitingReader == oldWaitingReader) { // The previous operation completed, so null out the "old" waiter // so we don't end up canceling the new operation. oldWaitingReader = null; } } else { newWaitingReader = new AsyncOperation <bool>(_parent._runContinuationsAsynchronously, cancellationToken); } parent._waitingReader = newWaitingReader; } oldWaitingReader?.TrySetCanceled(); return(newWaitingReader.ValueTaskOfT); }
public override ValueTask <T> ReadAsync(CancellationToken cancellationToken) { if (cancellationToken.IsCancellationRequested) { return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken))); } if (TryRead(out T item)) { return(new ValueTask <T>(item)); } SingleConsumerUnboundedChannel <T> parent = _parent; AsyncOperation <T> oldBlockedReader, newBlockedReader; lock (parent.SyncObj) { // Now that we hold the lock, try reading again. if (TryRead(out item)) { return(new ValueTask <T>(item)); } // If no more items will be written, fail the read. if (parent._doneWriting != null) { return(ChannelUtilities.GetInvalidCompletionValueTask <T>(parent._doneWriting)); } // Try to use the singleton reader. If it's currently being used, then the channel // is being used erroneously, and we cancel the outstanding operation. oldBlockedReader = parent._blockedReader; if (!cancellationToken.CanBeCanceled && _readerSingleton.TryOwnAndReset()) { newBlockedReader = _readerSingleton; if (newBlockedReader == oldBlockedReader) { // The previous operation completed, so null out the "old" reader // so we don't end up canceling the new operation. oldBlockedReader = null; } } else { newBlockedReader = new AsyncOperation <T>(_parent._runContinuationsAsynchronously, cancellationToken); } parent._blockedReader = newBlockedReader; } oldBlockedReader?.TrySetCanceled(); return(newBlockedReader.ValueTaskOfT); }
public override ValueTask <T> ReadAsync(CancellationToken cancellationToken) { if (cancellationToken.IsCancellationRequested) { return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken))); } // Dequeue an item if we can. UnboundedChannel <T> parent = _parent; if (parent._items.TryDequeue(out T item)) { CompleteIfDone(parent); return(new ValueTask <T>(item)); } lock (parent.SyncObj) { parent.AssertInvariants(); // Try to dequeue again, now that we hold the lock. if (parent._items.TryDequeue(out item)) { CompleteIfDone(parent); return(new ValueTask <T>(item)); } // There are no items, so if we're done writing, fail. if (parent._doneWriting != null) { return(ChannelUtilities.GetInvalidCompletionValueTask <T>(parent._doneWriting)); } // If we're able to use the singleton reader, do so. if (!cancellationToken.CanBeCanceled) { AsyncOperation <T> singleton = _readerSingleton; if (singleton.TryOwnAndReset()) { parent._blockedReaders.EnqueueTail(singleton); return(singleton.ValueTaskOfT); } } // Otherwise, create and queue a reader. var reader = new AsyncOperation <T>(parent._runContinuationsAsynchronously, cancellationToken); parent._blockedReaders.EnqueueTail(reader); return(reader.ValueTaskOfT); } }
public override ValueTask <T> ReadAsync(CancellationToken cancellationToken) { if (cancellationToken.IsCancellationRequested) { return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken))); } BoundedChannel <T> parent = _parent; lock (parent.SyncObj) { parent.AssertInvariants(); // If there are any items, hand one back. if (!parent._items.IsEmpty) { return(new ValueTask <T>(DequeueItemAndPostProcess())); } // There weren't any items. If we're done writing so that there // will never be more items, fail. if (parent._doneWriting != null) { return(ChannelUtilities.GetInvalidCompletionValueTask <T>(parent._doneWriting)); } // If we're able to use the singleton reader, do so. if (!cancellationToken.CanBeCanceled) { AsyncOperation <T> singleton = _readerSingleton; if (singleton.TryOwnAndReset()) { parent._blockedReaders.EnqueueTail(singleton); return(singleton.ValueTaskOfT); } } // Otherwise, queue a reader. Note that in addition to checking whether synchronous continuations were requested, // we also check whether the supplied cancellation token can be canceled. The writer calls UnregisterCancellation // while holding the lock, and if a callback needs to be unregistered and is currently running, it needs to wait // for that callback to complete so that the subsequent code knows it won't be contending with another thread // trying to complete the operation. However, if we allowed a synchronous continuation from this operation, that // cancellation callback could end up running arbitrary code, including code that called back into the reader or // writer and tried to take the same lock held by the thread running UnregisterCancellation... deadlock. As such, // we only allow synchronous continuations here if both a) the caller requested it and the token isn't cancelable. var reader = new AsyncOperation <T>(parent._runContinuationsAsynchronously | cancellationToken.CanBeCanceled, cancellationToken); parent._blockedReaders.EnqueueTail(reader); return(reader.ValueTaskOfT); } }
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken) { if (cancellationToken.IsCancellationRequested) { return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken))); } UnboundedChannel <T> parent = _parent; lock (parent.SyncObj) { parent.AssertInvariants(); // If there are any items, return one. if (parent._items.TryDequeue(out T item)) { // Dequeue an item if (parent._doneWriting != null && parent._items.IsEmpty) { // If we've now emptied the items queue and we're not getting any more, complete. ChannelUtilities.Complete(parent._completion, parent._doneWriting); } return(new ValueTask <T>(item)); } // There are no items, so if we're done writing, fail. if (parent._doneWriting != null) { return(ChannelUtilities.GetInvalidCompletionValueTask <T>(parent._doneWriting)); } // If we're able to use the singleton reader, do so. if (!cancellationToken.CanBeCanceled) { AsyncOperation <T> singleton = _readerSingleton; if (singleton.TryOwnAndReset()) { parent._blockedReaders.EnqueueTail(singleton); return(singleton.ValueTaskOfT); } } // Otherwise, create and queue a reader. var reader = new AsyncOperation <T>(parent._runContinuationsAsynchronously, cancellationToken); parent._blockedReaders.EnqueueTail(reader); return(reader.ValueTaskOfT); } }
public override ValueTask <bool> WaitToReadAsync(CancellationToken cancellationToken) { if (cancellationToken.IsCancellationRequested) { return(new ValueTask <bool>(Task.FromCanceled <bool>(cancellationToken))); } if (!_parent._items.IsEmpty) { return(new ValueTask <bool>(true)); } UnboundedChannel <T> parent = _parent; lock (parent.SyncObj) { parent.AssertInvariants(); // Try again to read now that we're synchronized with writers. if (!parent._items.IsEmpty) { return(new ValueTask <bool>(true)); } // There are no items, so if we're done writing, there's never going to be data available. if (parent._doneWriting != null) { return(parent._doneWriting != ChannelUtilities.s_doneWritingSentinel ? new ValueTask <bool>(Task.FromException <bool>(parent._doneWriting)) : new ValueTask <bool>(false)); } // If we're able to use the singleton waiter, do so. if (!cancellationToken.CanBeCanceled) { AsyncOperation <bool> singleton = _waiterSingleton; if (singleton.TryOwnAndReset()) { ChannelUtilities.QueueWaiter(ref parent._waitingReadersTail, singleton); return(singleton.ValueTaskOfT); } } // Otherwise, create and queue a waiter. var waiter = new AsyncOperation <bool>(parent._runContinuationsAsynchronously, cancellationToken); ChannelUtilities.QueueWaiter(ref parent._waitingReadersTail, waiter); return(waiter.ValueTaskOfT); } }
public override ValueTask <bool> WaitToReadAsync(CancellationToken cancellationToken) { if (cancellationToken.IsCancellationRequested) { return(new ValueTask <bool>(Task.FromCanceled <bool>(cancellationToken))); } BoundedChannel <T> parent = _parent; lock (parent.SyncObj) { parent.AssertInvariants(); // If there are any items available, a read is possible. if (!parent._items.IsEmpty) { return(new ValueTask <bool>(true)); } // There were no items available, so if we're done writing, a read will never be possible. if (parent._doneWriting != null) { return(parent._doneWriting != ChannelUtilities.s_doneWritingSentinel ? new ValueTask <bool>(Task.FromException <bool>(parent._doneWriting)) : new ValueTask <bool>(false)); } // There were no items available, but there could be in the future, so ensure // there's a blocked reader task and return it. // If we're able to use the singleton waiter, do so. if (!cancellationToken.CanBeCanceled) { AsyncOperation <bool> singleton = _waiterSingleton; if (singleton.TryOwnAndReset()) { ChannelUtilities.QueueWaiter(ref parent._waitingReadersTail, singleton); return(singleton.ValueTaskOfT); } } // Otherwise, queue a reader. var waiter = new AsyncOperation <bool>(parent._runContinuationsAsynchronously, cancellationToken); ChannelUtilities.QueueWaiter(ref _parent._waitingReadersTail, waiter); return(waiter.ValueTaskOfT); } }
public override ValueTask <T> ReadAsync(CancellationToken cancellationToken) { if (cancellationToken.IsCancellationRequested) { return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken))); } BoundedChannel <T> parent = _parent; lock (parent.SyncObj) { parent.AssertInvariants(); // If there are any items, hand one back. if (!parent._items.IsEmpty) { return(new ValueTask <T>(DequeueItemAndPostProcess())); } // There weren't any items. If we're done writing so that there // will never be more items, fail. if (parent._doneWriting != null) { return(ChannelUtilities.GetInvalidCompletionValueTask <T>(parent._doneWriting)); } // If we're able to use the singleton reader, do so. if (!cancellationToken.CanBeCanceled) { AsyncOperation <T> singleton = _readerSingleton; if (singleton.TryOwnAndReset()) { parent._blockedReaders.EnqueueTail(singleton); return(singleton.ValueTaskOfT); } } // Otherwise, queue the reader. var reader = new AsyncOperation <T>(parent._runContinuationsAsynchronously, cancellationToken); parent._blockedReaders.EnqueueTail(reader); return(reader.ValueTaskOfT); } }