Asynchronous socket reading: the initiating thread must not be exited - what to do?

Question

I have a NetworkStream which I read asynchronously (using async/await)

await Task<int>.Factory.FromAsync((cb, state) => stream.BeginRead(buffer, offset, readLen - offset), stream.EndRead, null);

Unfortunatly, an io exception sometimes occurs: "The I/O operation has been aborted because of either a thread exit or an application request."

I believe I hit a requirement documented in Socke.EndReceive: http://msdn.microsoft.com/en-us/library/w7wtt64b.aspx . Which states:

All I/O initiated by a given thread is canceled when that thread exits. A pending asynchronous operation can fail if the thread exits before the operation completes.

Because the async method runs on the default scheduler, this requirement cannot be assured.

Is there a way around this? Do I need to start a dedicated Thread to initiate I/O?

best regards, Dirk

Answer 1

I have asked the same question on the parallelextensions forum:

http://social.msdn.microsoft.com/Forums/en-US/parallelextensions/thread/d116f7b0-c8ee-4ce4-a9b8-4c38120e45a4

Basically, the ThreadPool will not stop any threads that has asynchronous I/O pending. So as long as one starts the socket operation on the ThreadPool this problem should not occur.

Answer 2

I would recommend using dedicated I/O threads that never terminate. That is what a lot of real-world code does.

One of the best ways to do it is to have the threads loop around GetQueuedCompletionStatus. If you need to make one of the I/O threads perform an I/O operation, call either PostQueuedCompletionStatus or QueueUserAPC to get the I/O thread to post the operation.

CAUTION: You must handle the case where these operations fail. QueueUserAPC, for example, can fail if too many APCs are already queued.