RFR 8177932 (process) java/lang/ProcessHandle/OnExitTest.java failed with "Process A should not be alive"

[Roger Riggs]

Hi Frank

Thanks for the review.

On 9/6/2017 1:41 AM, Frank Yuan wrote:
> Hi Roger
>
> I think this is the cause and I believe the patch will work.
>
> However, I have the following concern and minor comments:
> a. Is it possible that following scenario happens?
>     1. process A exits
>     2. Completion thread in onExist runs and gets 0 as origStart, and then sleeps 5s
>     3. process reaper thread reaps the process A, and then the pid is reused
>     4. Completion thread gets a value as startTime, and then has to wait the new process termination
>    I am not sure if the startTime may be zero except the process is a zombie, if the startTime may be zero only when the process is a zombie, we can change the condition to: if (startTime > 0 && startTime != origStart), otherwise we can't avoid such scenario, but if ProcessHandleImpl.onExit() passes startTime field to function completion, it may be a little bit better, at least, onExit() can be consistent with isAlive().
Note that the startTime in the ProcessHandle is acquired by 
ProcessHandle.of which uses isAlive,
and may be 0.
StartTime is optional and the provision to ignore startTime = 0 is 
intended to cover cases
where the underlying operating system did not or could not provide a 
reasonable start time.

We have not see any issues with pid re-use and I would prefer to avoid 
over engineering the code
for a non-issue.
With the proposed fix, the onExit completion handler and isAlive are 
consistent.

>
> b. Should we rollback the change of JDK-8184808, at least, update the comment in that change?
I'll update the comment.  Double checking using kill seems to be more 
reliable.
>
> c. Should we remove @key intermittent and the debug info added in JDK-8183019?

I'd prefer to leave them for some to make sure the issue does not re-appear.
I created a subtask to re-check in 2 months.

Roger

>
> Thanks
> Frank
>
>> -----Original Message-----
>> From: core-libs-dev [mailto:core-libs-dev-bounces at openjdk.java.net] On Behalf Of Roger Riggs
>> Subject: RFR 8177932 (process) java/lang/ProcessHandle/OnExitTest.java failed with "Process A should not be alive"
>>
>> Please review a fix for an intermittent issue with ProcessHandle.onExit.
>> On Solaris, the start time of a process reported through
>> /proc/pid/psinfo changes to
>> zero when the process is exiting.  The onExit implementation incorrectly
>> interpreted zero
>> meaning the pid had been re-used and the process was no longer alive.
>> However,
>> ProcessHandle.isAlive considered zero to be missing information and the
>> process was still alive.
>>
>> Webrev:
>>     http://cr.openjdk.java.net/~rriggs/webrev-onexit-8177932/
>>
>> Issue:
>>     https://bugs.openjdk.java.net/browse/JDK-8177932
>>
>> Thanks, Roger
>