/// <summary>
/// Writes a new buffer into the channel. The task returned by this operation only completes when the next
/// Read has been queued, or the Reader has completed, since the buffer provided here needs to be kept alive
/// until the matching Read finishes (because we don't have ownership tracking when working with unowned buffers)
/// </summary>
/// <param name="buffer"></param>
/// <param name="cancellationToken"></param>
/// <returns></returns>
// Called by the WRITER
public async Task WriteAsync(OwnedMemory <byte> buffer, CancellationToken cancellationToken)
{
// If Writing has stopped, why is the caller writing??
if (Writing.Status != TaskStatus.WaitingForActivation)
{
throw new OperationCanceledException("Writing has ceased on this Channel");
}
// If Reading has stopped, we cancel. We don't write unless there's a reader ready in this channel.
if (Reading.Status != TaskStatus.WaitingForActivation)
{
throw new OperationCanceledException("Reading has ceased on this Channel");
}
// Register for cancellation on this token for the duration of the write
using (cancellationToken.Register(state => ((UnownedBufferChannel)state).CancelWriter(), this))
{
// Wait for reading to start
await ReadingStarted;
// Cancel this task if this write is cancelled
cancellationToken.ThrowIfCancellationRequested();
// Allocate a new segment to hold the buffer being written.
using (var segment = new BufferSegment(buffer))
{
segment.End = buffer.Memory.Length;
if (_head == null || _head.ReadableBytes == 0)
{
// Update the head to point to the head of the buffer.
_head = segment;
}
else if (_tail != null)
{
// Add this segment to the end of the chain
_tail.Next = segment;
}
// Always update tail to the buffer's tail
_tail = segment;
// Trigger the continuation
Complete();
// Wait for another read to come (or for the end of Reading, which will also trigger this gate to open) in before returning
await _readWaiting;
if (_head.ReadableBytes > 0)
{
// We need to preserve any buffers that haven't been consumed
_head = BufferSegment.Clone(new ReadCursor(_head), new ReadCursor(_tail, _tail?.End ?? 0), out _tail);
}
}
// Cancel this task if this write is cancelled
cancellationToken.ThrowIfCancellationRequested();
}
}
private ReadableBuffer(ref ReadableBuffer buffer)
{
var begin = buffer._start;
var end = buffer._end;
BufferSegment segmentTail;
var segmentHead = BufferSegment.Clone(begin, end, out segmentTail);
begin = new ReadCursor(segmentHead);
end = new ReadCursor(segmentTail, segmentTail.End);
_start = begin;
_end = end;
_length = buffer._length;
begin.TryGetBuffer(end, out _first, out begin);
}
private ReadableBuffer(ref ReadableBuffer buffer)
{
var begin = buffer._start;
var end = buffer._end;
BufferSegment segmentTail;
var segmentHead = BufferSegment.Clone(begin, end, out segmentTail);
begin = new ReadCursor(segmentHead);
end = new ReadCursor(segmentTail, segmentTail.End);
_start = begin;
_end = end;
_isOwner = true;
_first = buffer._first;
_length = buffer._length;
}
internal void Append(ReadableBuffer buffer)
{
if (buffer.IsEmpty)
{
return; // nothing to do
}
EnsureAlloc();
BufferSegment clonedEnd;
var clonedBegin = BufferSegment.Clone(buffer.Start, buffer.End, out clonedEnd);
if (_writingHead == null)
{
// No active write
if (_commitHead == null)
{
// No allocated buffers yet, not locking as _readHead will be null
_commitHead = clonedBegin;
}
else
{
Debug.Assert(_commitHead.Next == null);
// Allocated buffer, append as next segment
_commitHead.Next = clonedBegin;
}
}
else
{
Debug.Assert(_writingHead.Next == null);
// Active write, append as next segment
_writingHead.Next = clonedBegin;
}
// Move write head to end of buffer
_writingHead = clonedEnd;
}