// Reading
void IPipeReader.Advance(ReadCursor consumed, ReadCursor examined)
{
BufferSegment returnStart = null;
BufferSegment returnEnd = null;
// Reading commit head shared with writer
Action continuation = null;
lock (_sync)
{
var examinedEverything = examined.Segment == _commitHead && examined.Index == _commitHeadIndex;
if (!consumed.IsDefault)
{
if (_readHead == null)
{
PipelinesThrowHelper.ThrowInvalidOperationException(ExceptionResource.AdvanceToInvalidCursor);
return;
}
returnStart = _readHead;
returnEnd = consumed.Segment;
// Check if we crossed _maximumSizeLow and complete backpressure
var consumedBytes = ReadCursor.GetLength(returnStart, returnStart.Start, consumed.Segment, consumed.Index);
var oldLength = _length;
_length -= consumedBytes;
if (oldLength >= _maximumSizeLow &&
_length < _maximumSizeLow)
{
continuation = _writerAwaitable.Complete();
}
// Check if we consumed entire last segment
// if we are going to return commit head
// we need to check that there is no writing operation that
// might be using tailspace
if (consumed.Index == returnEnd.End &&
!(_commitHead == returnEnd && _writingState.IsActive))
{
var nextBlock = returnEnd.Next;
if (_commitHead == returnEnd)
{
_commitHead = nextBlock;
_commitHeadIndex = nextBlock?.Start ?? 0;
}
_readHead = nextBlock;
returnEnd = nextBlock;
}
else
{
_readHead = consumed.Segment;
_readHead.Start = consumed.Index;
}
}
// We reset the awaitable to not completed if we've examined everything the producer produced so far
// but only if writer is not completed yet
if (examinedEverything && !_writerCompletion.IsCompleted)
{
// Prevent deadlock where reader awaits new data and writer await backpressure
if (!_writerAwaitable.IsCompleted)
{
PipelinesThrowHelper.ThrowInvalidOperationException(ExceptionResource.BackpressureDeadlock);
}
_readerAwaitable.Reset();
}
_readingState.End(ExceptionResource.NoReadToComplete);
}
while (returnStart != null && returnStart != returnEnd)
{
returnStart.Dispose();
returnStart = returnStart.Next;
}
TrySchedule(_writerScheduler, continuation);
}
