/// <summary>Dequeues an item, and then fixes up our state around writers and completion.</summary>
/// <returns>The dequeued item.</returns>
private T DequeueItemAndPostProcess()
{
Debug.Assert(Monitor.IsEntered(SyncObj));
// Dequeue an item.
T item = _items.DequeueHead();
// If we're now empty and we're done writing, complete the channel.
if (_doneWriting != null && _items.IsEmpty)
{
ChannelUtilities.Complete(_completion, _doneWriting);
}
// If there are any writers blocked, there's now room for at least one
// to be promoted to have its item moved into the items queue. We need
// to loop while trying to complete the writer in order to find one that
// hasn't yet been canceled (canceled writers transition to canceled but
// remain in the physical queue).
while (!_blockedWriters.IsEmpty)
{
WriterInteractor <T> w = _blockedWriters.DequeueHead();
if (w.Success(default(VoidResult)))
{
_items.EnqueueTail(w.Item);
return(item);
}
}
// There was no blocked writer, so see if there's a WaitToWriteAsync
// we should wake up.
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: true);
// Return the item
return(item);
}
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));
}
}
private bool TryComplete(Exception error = null)
{
bool completeTask;
lock (SyncObj)
{
AssertInvariants();
// If we've already marked the channel as completed, bail.
if (_doneWriting != null)
{
return(false);
}
// Mark that we're done writing.
_doneWriting = error ?? ChannelUtilities.DoneWritingSentinel;
completeTask = _items.IsEmpty;
}
// If there are no items in the queue, complete the channel's task,
// as no more data can possibly arrive at this point. We do this outside
// of the lock in case we'll be running synchronous completions, and we
// do it before completing blocked/waiting readers, so that when they
// wake up they'll see the task as being completed.
if (completeTask)
{
ChannelUtilities.Complete(_completion, error);
}
// At this point, _blockedReaders/Writers and _waitingReaders/Writers will not be mutated:
// they're only mutated by readers/writers while holding the lock, and only if _doneWriting is null.
// We also know that only one thread (this one) will ever get here, as only that thread
// will be the one to transition from _doneWriting false to true. As such, we can
// freely manipulate _blockedReaders and _waitingReaders without any concurrency concerns.
ChannelUtilities.FailInteractors <ReaderInteractor <T>, T>(_blockedReaders, error);
ChannelUtilities.FailInteractors <WriterInteractor <T>, VoidResult>(_blockedWriters, error);
ChannelUtilities.WakeUpWaiters(ref _waitingReaders, result: false);
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: false);
// Successfully transitioned to completed.
return(true);
}
private Task WriteAsync(T item, CancellationToken cancellationToken = default(CancellationToken))
{
if (cancellationToken.IsCancellationRequested)
{
return(Task.FromCanceled(cancellationToken));
}
lock (SyncObj)
{
// Fail if we've already completed
if (_completion.Task.IsCompleted)
{
return
(_completion.Task.IsCanceled ? Task.FromCanceled <T>(new CancellationToken(true)) :
Task.FromException <T>(
_completion.Task.IsFaulted ?
ChannelUtilities.CreateInvalidCompletionException(_completion.Task.Exception.InnerException) :
ChannelUtilities.CreateInvalidCompletionException()));
}
// Try to find a reader to pair with. Canceled readers remain in the queue,
// so we need to loop until we find one.
while (!_blockedReaders.IsEmpty)
{
ReaderInteractor <T> r = _blockedReaders.DequeueHead();
if (r.Success(item))
{
return(Task.CompletedTask);
}
}
// No reader was available. Queue the writer.
var w = WriterInteractor <T> .Create(true, cancellationToken, item);
_blockedWriters.EnqueueTail(w);
// And let any waiting readers know it's their lucky day.
ChannelUtilities.WakeUpWaiters(ref _waitingReaders, result: true);
return(w.Task);
}
}
private bool TryComplete(Exception error = null)
{
lock (SyncObj)
{
AssertInvariants();
// Mark the channel as being done. Since there's no buffered data, we can complete immediately.
if (_completion.Task.IsCompleted)
{
return(false);
}
ChannelUtilities.Complete(_completion, error);
// Fail any blocked readers/writers, as there will be no writers/readers to pair them with.
ChannelUtilities.FailInteractors <ReaderInteractor <T>, T>(_blockedReaders, ChannelUtilities.CreateInvalidCompletionException(error));
ChannelUtilities.FailInteractors <WriterInteractor <T>, VoidResult>(_blockedWriters, ChannelUtilities.CreateInvalidCompletionException(error));
// Let any waiting readers and writers know there won't be any more data
ChannelUtilities.WakeUpWaiters(ref _waitingReaders, result: false, error: error);
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: false, error: error);
}
return(true);
}
