A Bug about the JVM Attach mechanism

[Yasumasa Suenaga]

Hi,

 >> 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.

How about this change?
   http://cr.openjdk.java.net/~ysuenaga/JDK-8225690/proposal.2/

I think it can fix both JDK-8225690 and JDK-8225193.

This webrev implements for Linux only.
If we work further based on this, we need to implement 
AttachListener::check_socket_file() for each OS's implementation.


Thanks,

Yasumasa


On 2019/06/21 23:16, Yasumasa Suenaga wrote:
> 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