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));
}
// Otherwise, queue the reader.
var reader = ReaderInteractor <T> .Create(parent._runContinuationsAsynchronously, cancellationToken);
parent._blockedReaders.EnqueueTail(reader);
return(new ValueTask <T>(reader.Task));
}
}
/// <summary>Wake up all of the waiters and null out the field.</summary>
/// <param name="waiters">The waiters.</param>
/// <param name="result">The value with which to complete each waiter.</param>
internal static void WakeUpWaiters(ref ReaderInteractor <bool> waiters, bool result)
{
ReaderInteractor <bool> w = waiters;
if (w != null)
{
w.Success(result);
waiters = null;
}
}
/// <summary>Wake up all of the waiters and null out the field.</summary>
/// <param name="waiters">The waiters.</param>
/// <param name="result">The success value with which to complete each waiter if <paramref name="error">error</paramref> is null.</param>
/// <param name="error">The failure with which to cmplete each waiter, if non-null.</param>
internal static void WakeUpWaiters(ref ReaderInteractor <bool> waiters, bool result, Exception error = null)
{
ReaderInteractor <bool> w = waiters;
if (w != null)
{
if (error != null)
{
w.Fail(error);
}
else
{
w.Success(result);
}
waiters = null;
}
}
/// <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);
}
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);
}
}
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));
}
// Otherwise, queue the reader.
var reader = ReaderInteractor <T> .Create(parent._runContinuationsAsynchronously, cancellationToken);
parent._blockedReaders.EnqueueTail(reader);
return(new ValueTask <T>(reader.Task));
}
}
