private ValueTask <T> ReadAsync(CancellationToken cancellationToken = default(CancellationToken))
{
// Fast-path cancellation check
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
AssertInvariants();
// If there are any items, hand one back.
if (!_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 (_doneWriting != null)
{
return(ChannelUtilities.GetErrorValueTask <T>(_doneWriting));
}
// Otherwise, queue the reader.
var reader = ReaderInteractor <T> .Create(_runContinuationsAsynchronously, cancellationToken);
_blockedReaders.EnqueueTail(reader);
return(new ValueTask <T>(reader.Task));
}
}
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
// Now that we hold the lock, try reading again.
T item;
if (TryRead(out item))
{
return(new ValueTask <T>(item));
}
// If no more items will be written, fail the read.
if (_doneWriting != null)
{
return(ChannelUtilities.GetInvalidCompletionValueTask <T>(_doneWriting));
}
Debug.Assert(_blockedReader == null || ((_blockedReader as ReaderInteractor <T>)?.Task.IsCanceled ?? false),
"Incorrect usage; multiple outstanding reads were issued against this single-consumer channel");
// Store the reader to be completed by a writer.
ReaderInteractor <T> reader = ReaderInteractor <T> .Create(_runContinuationsAsynchronously, cancellationToken);
_blockedReader = reader;
return(new ValueTask <T>(reader.Task));
}
}
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
AssertInvariants();
// If we're already completed, nothing to read.
if (_completion.Task.IsCompleted)
{
return(new ValueTask <T>(
_completion.Task.IsCanceled ? Task.FromCanceled <T>(new CancellationToken(true)) :
Task.FromException <T>(
_completion.Task.IsFaulted ?
ChannelUtilities.CreateInvalidCompletionException(_completion.Task.Exception.InnerException) :
ChannelUtilities.CreateInvalidCompletionException())));
}
// If there are any blocked writers, find one to pair up with
// and get its data. Writers that got canceled will remain in the queue,
// so we need to loop to skip past them.
while (!_blockedWriters.IsEmpty)
{
WriterInteractor <T> w = _blockedWriters.DequeueHead();
if (w.Success(default(VoidResult)))
{
return(new ValueTask <T>(w.Item));
}
}
// No writer found to pair with. Queue the reader.
var r = ReaderInteractor <T> .Create(true, cancellationToken);
_blockedReaders.EnqueueTail(r);
// And let any waiting writers know it's their lucky day.
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: true);
return(new ValueTask <T>(r.Task));
}
}
/// <summary>Gets or creates a "waiter" (e.g. WaitForRead/WriteAsync) interactor.</summary>
/// <param name="waiter">The field storing the waiter interactor.</param>
/// <param name="runContinuationsAsynchronously">true to force continuations to run asynchronously; otherwise, false.</param>
/// <param name="cancellationToken">The token to use to cancel the wait.</param>
internal static Task <bool> GetOrCreateWaiter(ref ReaderInteractor <bool> waiter, bool runContinuationsAsynchronously, CancellationToken cancellationToken)
{
// Get the existing waiters interactor.
ReaderInteractor <bool> w = waiter;
// If there isn't one, create one. This explicitly does not include the cancellation token,
// as we reuse it for any number of waiters that overlap.
if (w == null)
{
waiter = w = ReaderInteractor <bool> .Create(runContinuationsAsynchronously);
}
// If the cancellation token can't be canceled, then just return the waiter task.
// If it can, we need to return a task that will complete when the waiter task does but that can also be canceled.
// Easiest way to do that is with a cancelable continuation.
return(cancellationToken.CanBeCanceled ?
w.Task.ContinueWith(t => t.Result, cancellationToken, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default) :
w.Task);
}
private Task <bool> WaitToReadAsync(CancellationToken cancellationToken = default)
{
// Outside of the lock, check if there are any items waiting to be read. If there are, we're done.
if (!_items.IsEmpty)
{
return(ChannelUtilities.TrueTask);
}
// Now check for cancellation.
if (cancellationToken.IsCancellationRequested)
{
return(Task.FromCanceled <bool>(cancellationToken));
}
ReaderInteractor <bool> oldWaiter = null, newWaiter;
lock (SyncObj)
{
// Again while holding the lock, check to see if there are any items available.
if (!_items.IsEmpty)
{
return(ChannelUtilities.TrueTask);
}
// There aren't any items; if we're done writing, there never will be more items.
if (_doneWriting != null)
{
return(_doneWriting != ChannelUtilities.DoneWritingSentinel ?
Task.FromException <bool>(_doneWriting) :
ChannelUtilities.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 = _waitingReader;
_waitingReader = newWaiter = ReaderInteractor <bool> .Create(_runContinuationsAsynchronously, cancellationToken);
}
oldWaiter?.TrySetCanceled();
return(newWaiter.Task);
}
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
AssertInvariants();
// If there are any items, return one.
T item;
if (_items.TryDequeue(out item))
{
// Dequeue an item
if (_doneWriting != null && _items.IsEmpty)
{
// If we've now emptied the items queue and we're not getting any more, complete.
ChannelUtilities.Complete(_completion, _doneWriting);
}
return(new ValueTask <T>(item));
}
// There are no items, so if we're done writing, fail.
if (_doneWriting != null)
{
return(ChannelUtilities.GetInvalidCompletionValueTask <T>(_doneWriting));
}
// Otherwise, queue the reader.
ReaderInteractor <T> reader = ReaderInteractor <T> .Create(_runContinuationsAsynchronously, cancellationToken);
_blockedReaders.EnqueueTail(reader);
return(new ValueTask <T>(reader.Task));
}
}