/// <summary>Asynchronously writes an item to the channel.</summary>
/// <param name="item">The value to write to the channel.</param>
/// <param name="cancellationToken">A <see cref="CancellationToken"/> used to cancel the write operation.</param>
/// <returns>A <see cref="Task"/> that represents the asynchronous write operation.</returns>
public virtual Task WriteAsync(T item, CancellationToken cancellationToken = default(CancellationToken))
{
try
{
return
(cancellationToken.IsCancellationRequested ? Task.FromCanceled <T>(cancellationToken) :
TryWrite(item) ? Task.CompletedTask :
WriteAsyncCore(item, cancellationToken));
}
catch (Exception e)
{
return(Task.FromException(e));
}
async Task WriteAsyncCore(T innerItem, CancellationToken ct)
{
while (await WaitToWriteAsync(ct).ConfigureAwait(false))
{
if (TryWrite(innerItem))
{
return;
}
}
throw ChannelUtilities.CreateInvalidCompletionException();
}
}
/// <summary>Mark the channel as being complete, meaning no more items will be written to it.</summary>
/// <param name="error">Optional Exception indicating a failure that's causing the channel to complete.</param>
/// <exception cref="InvalidOperationException">The channel has already been marked as complete.</exception>
public void Complete(Exception error = null)
{
if (!TryComplete(error))
{
throw ChannelUtilities.CreateInvalidCompletionException();
}
}
private async Task WriteAsyncCore(T innerItem, CancellationToken ct)
{
while (await WaitToWriteAsync(ct).ConfigureAwait(false))
{
if (TryWrite(innerItem))
{
return;
}
}
throw ChannelUtilities.CreateInvalidCompletionException();
}
public override ValueTask WriteAsync(T item, CancellationToken cancellationToken) => cancellationToken.IsCancellationRequested ? new ValueTask(Task.FromCanceled(cancellationToken)) : TryWrite(item) ? default : new ValueTask(Task.FromException(ChannelUtilities.CreateInvalidCompletionException(_parent._doneWriting)));
public override bool TryComplete(Exception error)
{
UnboundedChannel <T> parent = _parent;
bool completeTask;
lock (parent.SyncObj)
{
parent.AssertInvariants();
// If we've already marked the channel as completed, bail.
if (parent._doneWriting != null)
{
return(false);
}
// Mark that we're done writing.
parent._doneWriting = error ?? ChannelUtilities.s_doneWritingSentinel;
completeTask = parent._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(parent._completion, error);
}
// At this point, _blockedReaders and _waitingReaders will not be mutated:
// they're only mutated by readers while holding the lock, and only if _doneWriting is null.
// freely manipulate _blockedReaders and _waitingReaders without any concurrency concerns.
ChannelUtilities.FailOperations <AsyncOperation <T>, T>(parent._blockedReaders, ChannelUtilities.CreateInvalidCompletionException(error));
ChannelUtilities.WakeUpWaiters(ref parent._waitingReadersTail, result: false, error: error);
// Successfully transitioned to completed.
return(true);
}
public override ValueTask WriteAsync(T item, CancellationToken cancellationToken) => // Writing always succeeds (unless we've already completed writing or cancellation has been requested), // so just TryWrite and return a completed task. cancellationToken.IsCancellationRequested ? new ValueTask(Task.FromCanceled(cancellationToken)) : TryWrite(item) ? default : new ValueTask(Task.FromException(ChannelUtilities.CreateInvalidCompletionException(_parent._doneWriting)));
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);
}