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)) :
public override bool TryWrite(T item)
{
SingleConsumerUnboundedChannel <T> parent = _parent;
while (true) // in case a reader was canceled and we need to try again
{
AsyncOperation <T> blockedReader = null;
AsyncOperation <bool> waitingReader = null;
lock (parent.SyncObj)
{
// If writing is completed, exit out without writing.
if (parent._doneWriting != null)
{
return(false);
}
// If there's a blocked reader, store it into a local for completion outside of the lock.
// If there isn't a blocked reader, queue the item being written; then if there's a waiting
blockedReader = parent._blockedReader;
if (blockedReader != null)
{
parent._blockedReader = null;
}
else
{
parent._items.Enqueue(item);
waitingReader = parent._waitingReader;
if (waitingReader == null)
{
return(true);
}
parent._waitingReader = null;
}
}
// If we get here, we grabbed a blocked or a waiting reader.
Debug.Assert((blockedReader != null) ^ (waitingReader != null), "Expected either a blocked or waiting reader, but not both");
// If we have a waiting reader, notify it that an item was written and exit.
if (waitingReader != null)
{
// If we get here, we grabbed a waiting reader.
waitingReader.TrySetResult(item: true);
return(true);
}
// Otherwise we have a blocked reader: complete it with the item being written.
// In the case of a ReadAsync(CancellationToken), it's possible the reader could
// have been completed due to cancellation by the time we get here. In that case,
// we'll loop around to try again so as not to lose the item being written.
Debug.Assert(blockedReader != null);
if (blockedReader.TrySetResult(item))
{
return(true);
}
}
}
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);
}
internal UnboundedChannelReader(SingleConsumerUnboundedChannel <T> parent)
{
_parent = parent;
_readerSingleton = new AsyncOperation <T>(parent._runContinuationsAsynchronously)
{
UnsafeState = ResettableValueTaskSource.States.Released
};
_waiterSingleton = new AsyncOperation <bool>(parent._runContinuationsAsynchronously)
{
UnsafeState = ResettableValueTaskSource.States.Released
};
}
public override bool TryRead(out T item)
{
SingleConsumerUnboundedChannel<T> parent = _parent;
if (parent._items.TryDequeue(out item))
{
if (parent._doneWriting != null && parent._items.IsEmpty)
{
ChannelUtilities.Complete(parent._completion, parent._doneWriting);
}
return true;
}
return false;
}
public override ValueTask <T> ReadAsync(CancellationToken cancellationToken)
{
{
return(TryRead(out T item) ?
new ValueTask <T>(item) :
ReadAsyncCore(cancellationToken));
}
ValueTask <T> ReadAsyncCore(CancellationToken ct)
{
SingleConsumerUnboundedChannel <T> parent = _parent;
if (ct.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(ct)));
}
lock (parent.SyncObj)
{
// Now that we hold the lock, try reading again.
if (TryRead(out T 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));
}
Debug.Assert(parent._blockedReader == null || parent._blockedReader.Task.IsCanceled,
"Incorrect usage; multiple outstanding reads were issued against this single-consumer channel");
// Store the reader to be completed by a writer.
var reader = ReaderInteractor <T> .Create(parent._runContinuationsAsynchronously, ct);
parent._blockedReader = reader;
return(new ValueTask <T>(reader.Task));
}
}
}
public override Task <bool> WaitToReadAsync(CancellationToken cancellationToken)
{
// Outside of the lock, check if there are any items waiting to be read. If there are, we're done.
return
(cancellationToken.IsCancellationRequested ? Task.FromCanceled <bool>(cancellationToken) :
!_parent._items.IsEmpty ? ChannelUtilities.s_trueTask :
WaitToReadAsyncCore(cancellationToken));
Task <bool> WaitToReadAsyncCore(CancellationToken ct)
{
SingleConsumerUnboundedChannel <T> parent = _parent;
ReaderInteractor <bool> oldWaiter = null, newWaiter;
lock (parent.SyncObj)
{
// Again while holding the lock, check to see if there are any items available.
if (!parent._items.IsEmpty)
{
return(ChannelUtilities.s_trueTask);
}
// 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 ?
Task.FromException <bool>(parent._doneWriting) :
ChannelUtilities.s_falseTask);
}
// Create the new waiter. We're a bit more tolerant of a stray waiting reader
// than we are of a blocked reader, as with usage patterns it's easier to leave one
// behind, so we just cancel any that may have been waiting around.
oldWaiter = parent._waitingReader;
parent._waitingReader = newWaiter = ReaderInteractor <bool> .Create(parent._runContinuationsAsynchronously, ct);
}
oldWaiter?.TrySetCanceled();
return(newWaiter.Task);
}
}
internal UnboundedChannelReader(SingleConsumerUnboundedChannel <T> parent)
{
_parent = parent;
_readerSingleton = new AsyncOperation <T>(parent._runContinuationsAsynchronously, pooled: true);
_waiterSingleton = new AsyncOperation <bool>(parent._runContinuationsAsynchronously, pooled: true);
}
public override bool TryComplete(Exception error)
{
AsyncOperation <T> blockedReader = null;
AsyncOperation <bool> waitingReader = null;
bool completeTask = false;
SingleConsumerUnboundedChannel <T> parent = _parent;
lock (parent.SyncObj)
{
// If we're already marked as complete, there's nothing more to do.
if (parent._doneWriting != null)
{
return(false);
}
// Mark as complete for writing.
parent._doneWriting = error ?? ChannelUtilities.s_doneWritingSentinel;
// If we have no more items remaining, then the channel needs to be marked as completed
// and readers need to be informed they'll never get another item. All of that needs
// to happen outside of the lock to avoid invoking continuations under the lock.
if (parent._items.IsEmpty)
{
completeTask = true;
if (parent._blockedReader != null)
{
blockedReader = parent._blockedReader;
parent._blockedReader = null;
}
if (parent._waitingReader != null)
{
waitingReader = parent._waitingReader;
parent._waitingReader = null;
}
}
}
// Complete the channel task if necessary
if (completeTask)
{
ChannelUtilities.Complete(parent._completion, error);
}
Debug.Assert(blockedReader == null || waitingReader == null, "There should only ever be at most one reader.");
// Complete a blocked reader if necessary
if (blockedReader != null)
{
error = ChannelUtilities.CreateInvalidCompletionException(error);
blockedReader.TrySetException(error);
}
// Complete a waiting reader if necessary. (We really shouldn't have both a blockedReader
// and a waitingReader, but it's more expensive to prevent it than to just tolerate it.)
if (waitingReader != null)
{
if (error != null)
{
waitingReader.TrySetException(error);
}
else
{
waitingReader.TrySetResult(item: false);
}
}
// Successfully completed the channel
return(true);
}
internal UnboundedChannelWriter(SingleConsumerUnboundedChannel <T> parent) => _parent = parent;