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Fixing Receive/Close race 

Fixing a race where removing the last message from the channel would trigger draining the event queue (in channel Completion continuation) which would prevent from raising the Received event for the very message that was read from the channel.
This commit is contained in:
moozzyk 2017-03-13 15:14:40 -07:00
parent 4bacbfeb05
commit 2f2d3a6f24
1 changed files with 11 additions and 1 deletions
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12
src/Microsoft.AspNetCore.Sockets.Client/Connection.cs
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@ -110,8 +110,16 @@ namespace Microsoft.AspNetCore.Sockets.Client
{
Interlocked.Exchange(ref _connectionState, ConnectionState.Disconnected);
_logger.LogDebug("Draining event queue");
// There is an inherent race between receive and close. Removing the last message from the channel
// makes Input.Completion task completed and runs this continuation. We need to await _receiveLoopTask
// to make sure that the message removed from the channel is processed before we drain the queue.
// There is a short window between we start the channel and assign the _receiveLoopTask a value.
// To make sure that _receiveLoopTask can be awaited (i.e. is not null) we need to await _startTask.
_logger.LogDebug("Ensuring all outstanding messages are processed.");
await _startTask;
await _receiveLoopTask;
_logger.LogDebug("Draining event queue");
await _eventQueue.Drain();
_logger.LogDebug("Raising Closed event");
@ -209,6 +217,8 @@ namespace Microsoft.AspNetCore.Sockets.Client
_logger.LogDebug("Scheduling raising Received event.");
var ignore = _eventQueue.Enqueue(() =>
{
_logger.LogDebug("Raising Received event.");
// Do not "simplify" - event handlers can be removed from a different thread
var receivedEventHandler = Received;
if (receivedEventHandler != null)