RFR 8056143: interrupted java/lang/management/MemoryMXBean/LowMemoryTest.java leaves running process

[Jaroslav Bachorik]

On 10/15/2014 10:11 AM, David Holmes wrote:
> On 15/10/2014 5:50 PM, Jaroslav Bachorik wrote:
>> On 10/15/2014 02:10 AM, David Holmes wrote:
>>> On 14/10/2014 8:46 PM, Jaroslav Bachorik wrote:
>>>> Please, review the following test change
>>>>
>>>> Issue : https://bugs.openjdk.java.net/browse/JDK-8056143
>>>> Webrev: http://cr.openjdk.java.net/~jbachorik/8056143/webrev.00
>>>>
>>>> The method jdk.testlibrary.ProcessTools.getOutput(process) waits for
>>>> the
>>>> given process to finish (process.waitFor()) before grabbing its
>>>> outputs.
>>>> However, the code does not handle the process.waitFor() being
>>>> interrupted correctly - it just goes ahead and tries to obtain the exit
>>>> code which will fail and leave the tested process running.
>>>>
>>>> The correct way is to forcibly destroy the process when
>>>> process.waitFor() is interrupted or throws ExecutionException to make
>>>> sure the process has actually exited before checking its exit code.
>>>
>>> Why is this correct? What gives the thread calling getOutput the right
>>> to terminate the target process just because that thread was interrupted
>>> while waiting? If the interrupting thread intended the interrupt to mean
>>> "forcibly terminate the process and interrupt all threads waiting on it"
>>> then that thread should be doing the termination _not_ the one that was
>>> interrupted!
>>
>> Process.waitFor() gets interrupted by a thread unknown to the actual
>> test case - probably the JTreg timeout thread. The interrupting thread
>> doesn't know that it is supposed to destroy a process. Once JTreg can
>> take care of cleaning up process tree upon exit this code wouldn't be
>> needed.
>>
>> I was contemplating adding the check for "null" returned from
>> ProcessTools.getOutput() and destroying the process inside the caller
>> code - but this would have the same results as doing it in
>> ProcessTools.getOutput() with the drawback of duplicating the same check
>> everywhere ProcessTools.getOutput() would be used.
>>
>> A silent postcondition of ProcessTools.getOuptut() is that the target
>> process has finished - and it holds for all the code paths except the
>> InterruptedException handler.
>
> That doesn't mean it is up to getOutput to forcibly terminate the
> process. Multi-process cancellation is tricky, and yes eventually jtreg
> will handle it. But this seems the wrong place to handle it now. Part of
> the flaw here is that getOutput should itself throw InterruptedException
> so that the caller is forced to deal with this - instead it just
> re-asserts the interrupt state. The caller has to be aware that the
> thread can be interrupted and do something appropriate - which may mean
> punting to its caller. This is akin to a thread catching
> InterruptedException and calling System.exit - it simply is not its job
> to make that kind of decision at that level!

There is no other decision to make. Not as it is written today. You can 
call ProcessTools.getOutput() and check whether the result is null and 
then end the test process. There is no other sensible action. The 
Process.waitFor() was interrupted you have no data to perform the checks 
against so the test will fail and as such it should stop any external 
processes it has started.

Yes, I can go through all the tests using ProcessTools.getOutput() and 
add `if (output == null) process.destroyForcible();` - would this make 
it a better solution than putting this logic inside 
ProcessTools.getOutput()?

-JB-

>
> David
>
>> -JB-
>>
>>
>>
>>>
>>> David
>>>
>>>> Thanks,
>>>>
>>>> -JB-
>>