ChallengeSpot the bug in the stream
Consider the following code:
This is meant to add timeout support for a stream.
There is a subtle bug in the code, can you spot it? What would be the implications here?
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Hmm. There is no cancellation of the Memory ReadAsync in case the Delay task completes first. ReadAsync will continue increasing the position which is not thread-safe, so there might be problems if another process continues to work on the stream after this method has finished.
To continue Nik's observation:
After you cancel the ReadAsync because of timing out, you still want to wait for the asTask to finish. Just because you told it to cancel, doesn't mean it actually can or did.
Also keep in mind that you will now need to catch the TaskCanceledException that ReadAsync will throw because of the 'timeout cancellation token'.
And when you start to use a 'timeout cancellation token', you can do
new CancellationToken(_delay)instead of using
Don't forget to create a linked cancellation token (but only if
cancellationToken.CanBeCanceled == true)
You should be awaiting
asTaskand returning that. You introduce the potential for deadlock when you call
Nicholas, can you elaborate? As far as I can see, asTask must have a result at line 26. And accessing Result when the task has a result doesn't do anything that can hurt us.
It is likely that ReadAsync almost always completes before Delay but in that case you are leaving dangling unfinished timer. This can lead to resource strain as you can have many read operations in progress generating more and more active Delay tasks and system timers. If the read operation doesn't time out you should always cancel the pending delay task. use
maybe add fast path for cancellationToken == default - skipping the whole timeout logic
The return value of WhenAny is Task<Task> - so the return value's Result is the Task that completed. Your if statement should check for
if (result.Result == delay)
Oh just noticed the await.. ignore my comment :)