A Bug about the JVM Attach mechanism

[Yasumasa Suenaga]

On 2019/06/21 22:51, David Holmes wrote:
> 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.

Yes, my proposal focuses to "multiple attach threads".
I shared my patch because it might help the work for this issue.

This patch would guard multithread-issue in Attach Listener.
So unix domain socket file will create just once.


Yasumasa


> 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