A Bug about the JVM Attach mechanism

[David Holmes]

Hi Yasumasa,

On 21/06/2019 5:12 am, Yasumasa Suenaga wrote:
> Hi,
> 
> Can we fix this issue like this webrev?
>    http://cr.openjdk.java.net/~ysuenaga/JDK-8225690/proposal/

I'm not clear how this addresses the issue with deleting the file? The 
file still has to exist IIUC for the mechanism to work.

This seems more suited to fixing the "multiple attach threads" problem.

David

> I could reproduce this issue with ConcAttachTest.java in it
> on my laptop.
> (Fedora 30 x64 on Hyper-V guest: Core i3-8145U x 2vcpu)
> 
> If we need to fix based on current implementation, I think
> we need to use atomic operation.
> But if we can refactor around here, we might be able to another approach 
> - e.g. using monitors/mutexes
> 
> 
> Thanks,
> 
> Yasumasa
> 
> 
> On 2019/06/21 5:49, David Holmes wrote:
>> Sorry it took me a while to understand the specifics of the problem. :)
>>
>> David
>>
>> On 20/06/2019 3:37 am, nijiaben wrote:
>>> Yes Alan, I mean this
>>> ------------------?Original?------------------
>>> *From: *?"Alan Bateman"<Alan.Bateman at oracle.com>;
>>> *Date: *?Thu, Jun 20, 2019 02:54 PM
>>> *To: *?"nijiaben"<nijiaben at perfma.com>; "David
>>> Holmes"<david.holmes at oracle.com>;
>>> "serviceability-dev"<serviceability-dev at openjdk.java.net>;
>>> "jdk8u-dev"<jdk8u-dev at openjdk.java.net>;
>>> "hotspot-runtime-dev"<hotspot-runtime-dev at openjdk.java.net>;
>>> *Subject: *?Re: A Bug about the JVM Attach mechanism
>>> On 20/06/2019 05:10, nijiaben wrote:
>>>   > :
>>>   > I know this mechanism, can we provide means of recovery to avoid
>>> unavailability caused by accidental deletion?
>>>   >
>>> Are you concerned about tmpreaper or cron jobs that periodically cleanup
>>> /tmp? There may indeed be an issue for applications that run for weeks
>>> or months. If someone is using jmap, jcmd or other tools using the
>>> attach API then it will trigger the attach listener to start. When they
>>> come back in a few weeks then the .java_pid<pid> file may have been
>>> removed so they cannot attach. Is this what what you are pointing out?
>>>
>>> -Alan