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Process cancelled tasks from SerialStream.Unix read/write request queues when a timeout occurs #55188

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Process cancelled tasks from SerialStream.Unix read/write request queues when a timeout occurs #55188

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20 changes: 20 additions & 0 deletions src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Unix.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -415,6 +415,7 @@ internal int Read(byte[] array, int offset, int count, int timeout)
}
catch (OperationCanceledException)
{
ProcessCancelledIORequests(_readQueue);
throw new TimeoutException();
}
}
Expand Down Expand Up @@ -506,6 +507,7 @@ internal void Write(byte[] array, int offset, int count, int timeout)
}
catch (OperationCanceledException)
{
ProcessCancelledIORequests(_writeQueue);
throw new TimeoutException();
}
}
Expand All @@ -527,6 +529,8 @@ private int EndReadWrite(IAsyncResult asyncResult)
}
catch (OperationCanceledException)
{
ProcessCancelledIORequests(_readQueue);
ProcessCancelledIORequests(_writeQueue);
throw new TimeoutException();
}
}
Expand Down Expand Up @@ -807,6 +811,22 @@ private static int DoIORequest(ConcurrentQueue<SerialStreamIORequest> q, Request
return 0;
}

private static void ProcessCancelledIORequests(ConcurrentQueue<SerialStreamIORequest> q)
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@krwq krwq Aug 12, 2021 •
edited
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I don't think this will be thread safe as is. Currently there is multiple threads which can enqueue and only one dequeuing. With this change you will have multiple threads potentially dequeueing. Since we do Peek & Dequeue here and IOLoop you might end up with one thread peeking and different one dequeuing. See i.e.

runtime/src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Unix.cs

Line 790 in 98efcdf

// assumes dequeue-ing happens on a single thread

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Instead consider calling this inside of the IOLoop in the idle state (make sure to write a comment about why we do that)

{
// assumes dequeue-ing happens on a single thread
while (q.TryPeek(out SerialStreamIORequest r))
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consider cleaning all completed instead, similarly as done here:

runtime/src/libraries/System.IO.Ports/src/System/IO/Ports/SerialStream.Unix.cs

Lines 793 to 798 in 98efcdf

if (r.IsCompleted)
{
q.TryDequeue(out _);
// take another item since we haven't processed anything
continue;
}

{
if (r.Task.IsCanceled)
{
q.TryDequeue(out _);
}
else
{
return;
}
}
}

private void IOLoop()
{
bool eofReceived = false;
Expand Down