Protocol version of Attach API

[David Holmes]

On 27/02/2019 8:48 am, Alex Menkov wrote:
> 
> On 02/26/2019 13:58, David Holmes wrote:
>> On 27/02/2019 7:50 am, Chris Plummer wrote:
>>>>> Also want to point out that this issue might be two-way: 8 can't 
>>>>> attach to 13 and 13 may have issues attaching to 8 (what happens 
>>>>> with the extra argument that is sent?).
>>>>
>>>> You can't expect an old release to accept new and unknown args. That 
>>>> is perfectly fine.
>>>
>>> But we should expect that you can attach from 13 to 8. If unknown 
>>> args are sent, we would need for them to be quietly ignored.
>>
>> That depends on how well the code was written in 8, but I think it 
>> perfectly fine to get an error if you try to send a command that 8 
>> doesn't (fully) understand.
> 
> Looks like AttachOperation::arg_count_max is used not just as max arg 
> count, but also to calculate packet size which needs to be read from the 
> socket on unix systems (it's expected to be the same for all 
> operations). So it cannot be easily fixed.

Yes that is the problem as I have now stated many times - it should be 
prpeared to read a variable sized packet, but instead expects a fixed 
size on. However it should be easily fixable. I'm testing Yasumasa's fix 
now.

> BTW as far as I got Windows if not affected. Looking into the code 
> (src/hotspot/os/windows/attachListener_windows.cpp) I suppose the 
> feature implemented by JDK-8215622 does not work at Windows as 
> Win32AttachListener still support only 3 args.

There were changes on Windows for JDK-8215622 in the Java code, but you 
are right that Win32AttachListener::enqueue only accepts and passes on 
three args! Yet the updated BasicJmapTest passes on windows ... or 
appears to, the log information for those specific tests is missing due 
to the "output overflow" problem.

I'm also double-checking Solaris.

> In my opinion it would be better to revert fix for JDK-8215622 and 
> rethink how to implement it without changing AttachOperation::arg_count_max

Let's see how Yasumasa's fix works out.

Thanks,
David

> --alex
> 
> 
>>
>> David
>>
>>
>>>
>>> Chris
>>>
>>>>
>>>> David
>>>> -----
>>>>
>>>>> Chris
>>>>>
>>>>>>
>>>>>>>
>>>>>>> ..Thomas
>>>>>>
>>>>>
>>>
>>>