JEP 425 (Virtual Threads) - Cancellation

[David Holmes]

On 2/05/2022 7:15 pm, Attila Kelemen wrote:
> Alan Bateman <Alan.Bateman at oracle.com> ezt írta (időpont: 2022. máj.
> 2., H, 9:42):
>>
>> Search for the sentence "To allow for interruption and cancellation, the
>> blocking I/O methods ..." in the Networking section of the JEP as it
>> deals with this topic.
> 
> That part seems to be only about sockets, while I would like to see the other
> most common I/O operations to address the problem. Sure, as David mentioned
> in a previous email, it is not a trivial change (I'm not even
> proposing that this JEP
> should include it, just that this would be a good time to release a cancellation
> JEP building on this virtual thread JEP), but still the current state is a major
> inconvenience. In fact, I just recently learned that, there can be a
> scenario where
> if you block on an `InputStream` (stdout/stderr of started process) of a started
> `Process`, then you will be trapped in the blocking call forever (even
> destroy/destroyForcibly of the process won't help), unless you steal and close
> the underlying `FileChannel` via reflection.

On the surface that seems like a bug in the Process API. Termination of 
the child process should be detected and the captured streams closed.

David

>> As David said, this is more in the area of the (still in draft)
>> Structured Concurrency JEP. There have been several prototypes that
>> explored the cancellation space. The draft JEP has an explicit non-goal
>> to provide a new cancellation mechanism but leaves the door open to
>> re-visiting in a future JEP.
> 
> I looked up the Structured Concurrency JEP, but the only one I have found
> is this draft: https://openjdk.java.net/jeps/8277129 However, this explicitly
> states that it will not address the current cancellation issues. That is, there
> are a lot of blocking APIs not declaring a thrown `InterruptedException`, and
> as far as I can see a JEP addressing cancellation should consider these
> cases as well. Can you point me to JEPs / discussion where cancellation
> issues were / are being considered?
> 
> 
> Thanks,
> Attila