Discussion about fixing deprecation in jdk.hotspot.agent

Wed Apr 1 22:16:13 UTC 2020

On 4/1/20 4:01 PM, Chris Plummer wrote:
> On 4/1/20 5:13 AM, Magnus Ihse Bursie wrote:
>>
>>
>> On 2020-04-01 12:22, Kevin Walls wrote:
>>> Hi Coleen and all -
>>>
>>> Given the choice I'd ask that we don't remove attach/detach because 
>>> it limits the scope of what a clhsdb can do in future. Commands like 
>>> jstack are a one-shot operation.  A Tool like clhsdb is ideally more 
>>> flexible than that.
>>>
>>> The SA is (I suggest) "too static" in its "there is one VM" 
>>> approach, so we can't write a Tool that attaches to multiple VMs. If 
>>> we remove attach/detach, it could not even gather information in a 
>>> series of requests.  This is not going to be in the product any time 
>>> soon, and maybe never, but it doesn't look right that we cut off 
>>> such experiments.
>>>
>>> Removing the Observer, yes would imply making detach into detach and 
>>> exit.  I think the clhsdb "attach" command would still work (once 
>>> only!) but is odd without detach (so do we make "bin/jhsdb clhsdb" 
>>> require parameters...).
>>>
>>> It looks like this changes the direction of the Tools in order to 
>>> remove the deprecation warnings.
>>>
>>> Magnus' webrev 
>>> http://cr.openjdk.java.net/~ihse/hotspot-agent-observer/webrev.01/ 
>>> does add/duplicate some code, but I like it for keeping things 
>>> working 8-)
>>
>> Here's an updated version of that approach that minimizes the amount 
>> of new code:
>>
>> http://cr.openjdk.java.net/~ihse/hotspot-agent-observer/webrev.03
>>
>> The difference is that I do not duplicate the classes themselves, I 
>> just subclass them to get a single point where the @SuppressWarnings 
>> can be put. The only change needed in the rest of the files is to 
>> make sure we import these classes instead of the ones in java.util.
>>
> HI Magnus,
>
> I think at this time this is probably the best approach. It's just two 
> new SA classes that are simple subclasses of Observer and Observable, 
> and a bunch new imports in any file that references them, right? I 
> would just suggest adding a comment to these two classes to indicate 
> why this is being done.
>

When I was looking at this, most of the files import the java.util 
version of Observer and Observable:

import java.util.Observable;
import java.util.Observer;

If you load the subclass, then these don't have to be changed in all the 
other files?

Coleen

> thanks,
>
> Chris
>> /Magnus
>>
>>>
>>>
>>> Thanks
>>> Kevin
>>>
>>>
>>> On 31/03/2020 22:20, coleen.phillimore at oracle.com wrote:
>>>>
>>>>
>>>> On 3/31/20 4:55 PM, Chris Plummer wrote:
>>>>> On 3/31/20 1:32 PM, coleen.phillimore at oracle.com wrote:
>>>>>>
>>>>>>
>>>>>> On 3/31/20 12:19 PM, Poonam Parhar wrote:
>>>>>>> Hello Coleen,
>>>>>>>
>>>>>>> Does the removal of this code only impact the 'reattach' 
>>>>>>> functionality, and it does not affect any commands available in 
>>>>>>> 'clhsdb' once it is attached to a core file? If that's true, 
>>>>>>> then I think it should be okay to remove this code.
>>>>>>
>>>>>> Hi Poonam,  Thank you for answering. Yes, this patch only removes 
>>>>>> the reattach functionality.  I tried out the other clhsdb 
>>>>>> commands from your wiki page, and they worked fine, including 
>>>>>> object and heap inspection.
>>>>> I'm trying to understand exactly when all these static initializes 
>>>>> are triggered. Is it only after you do an attach?
>>>>>
>>>>> The implementation of clhsdb reattach is exactly the same as doing 
>>>>> a detach followed by an attach to the same process. I'm not sure 
>>>>> how much value it has, but I think in general the removal of this 
>>>>> code means you can't detach and then attach to anything, even a 
>>>>> different pid. So "detach" might as well become "detach-and-exit", 
>>>>> because your clhsdb session is dead once you detach. Do we really 
>>>>> want to do this?
>>>>
>>>> Well, that was my question. It seems like you could just exit and 
>>>> start up jhsdb again and that's more like something someone would 
>>>> do just as easily.  Given the use cases that we've seen from 
>>>> sustaining, this appears to be unneeded functionality.
>>>>
>>>> The original mail was proposing adding more code to work around the 
>>>> deprecation messages.  It seems like more code should not be added 
>>>> for something that is unused.
>>>>
>>>> thanks,
>>>> Coleen
>>>>
>>>>>
>>>>> Chris
>>>>>>
>>>>>> Thanks,
>>>>>> Coleen
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Poonam
>>>>>>>
>>>>>>> On 3/31/20 5:34 AM, coleen.phillimore at oracle.com wrote:
>>>>>>>>
>>>>>>>> To answer my own question, this functionality is used to allow 
>>>>>>>> detach/reattach from {cl}hsdb.  Which seems to work on linux 
>>>>>>>> but not windows with this code removed.
>>>>>>>>
>>>>>>>> The next question is whether this is useful functionality to 
>>>>>>>> justify all this code (900+ and this new code that Magnus has 
>>>>>>>> added).  Can't you just exit and restart the clhsdb process on 
>>>>>>>> the core file or process?
>>>>>>>>
>>>>>>>> For the record, this is me playing with python to remove this 
>>>>>>>> code.
>>>>>>>>
>>>>>>>> http://cr.openjdk.java.net/~coleenp/2020/01/webrev/index.html
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Coleen
>>>>>>>>
>>>>>>>> On 3/30/20 3:04 PM, coleen.phillimore at oracle.com wrote:
>>>>>>>>>
>>>>>>>>> I was wondering why this is needed when debugging a core file, 
>>>>>>>>> which is the key thing we need the SA for:
>>>>>>>>>
>>>>>>>>>   /** This is used by both the debugger and any runtime 
>>>>>>>>> system. It is
>>>>>>>>>       the basic mechanism by which classes which mimic 
>>>>>>>>> underlying VM
>>>>>>>>>       functionality cause themselves to be initialized. The given
>>>>>>>>>       observer will be notified (with arguments (null, null)) 
>>>>>>>>> when the
>>>>>>>>>       VM is re-initialized, as well as when it registers 
>>>>>>>>> itself with
>>>>>>>>>       the VM. */
>>>>>>>>>   public static void registerVMInitializedObserver(Observer o) {
>>>>>>>>>     vmInitializedObservers.add(o);
>>>>>>>>>     o.update(null, null);
>>>>>>>>>   }
>>>>>>>>>
>>>>>>>>> It seems like if it isn't needed, we shouldn't add these 
>>>>>>>>> classes and remove their use.
>>>>>>>>>
>>>>>>>>> Coleen
>>>>>>>>>
>>>>>>>>> On 3/30/20 8:14 AM, Magnus Ihse Bursie wrote:
>>>>>>>>>> No opinions on this?
>>>>>>>>>>
>>>>>>>>>> /Magnus
>>>>>>>>>>
>>>>>>>>>> On 2020-03-25 23:34, Magnus Ihse Bursie wrote:
>>>>>>>>>>> Hi everyone,
>>>>>>>>>>>
>>>>>>>>>>> As a follow-up to the ongoing review for JDK-8241618, I have 
>>>>>>>>>>> also looked at fixing the deprecation warnings in 
>>>>>>>>>>> jdk.hotspot.agent. These fall in three broad categories:
>>>>>>>>>>>
>>>>>>>>>>> * Deprecation of the boxing type constructors (e.g. "new 
>>>>>>>>>>> Integer(42)").
>>>>>>>>>>>
>>>>>>>>>>> * Deprecation of java.util.Observer and Observable.
>>>>>>>>>>>
>>>>>>>>>>> * The rest (mostly Class.newInstance(), and a few number of 
>>>>>>>>>>> other odd deprecations)
>>>>>>>>>>>
>>>>>>>>>>> The first category is trivial to fix. The last category need 
>>>>>>>>>>> some special discussion. But the overwhelming majority of 
>>>>>>>>>>> deprecation warnings come from the use of Observer and 
>>>>>>>>>>> Observable. This really dwarfs anything else, and needs to 
>>>>>>>>>>> be handled first, otherwise it's hard to even spot the other 
>>>>>>>>>>> issues.
>>>>>>>>>>>
>>>>>>>>>>> My analysis of the situation is that the deprecation of 
>>>>>>>>>>> Observer and Observable seems a bit harsh, from the PoV of 
>>>>>>>>>>> jdk.hotspot.agent. Sure, it might be limited, but I think it 
>>>>>>>>>>> does exactly what is needed here. So the migration suggested 
>>>>>>>>>>> in Observable (java.beans or java.util.concurrent) seems 
>>>>>>>>>>> overkill. If there are genuine threading issues at play 
>>>>>>>>>>> here, this assumption might be wrong, and then maybe going 
>>>>>>>>>>> the j.u.c. route is correct.
>>>>>>>>>>>
>>>>>>>>>>> But if that's not, the main goal should be to stay with the 
>>>>>>>>>>> current implementation. One way to do this is to sprinkle 
>>>>>>>>>>> the code with @SuppressWarning. But I think a better way 
>>>>>>>>>>> would be to just implement our own Observer and Observable. 
>>>>>>>>>>> After all, the classes are trivial.
>>>>>>>>>>>
>>>>>>>>>>> I've made a mock-up of this solution, were I just copied the 
>>>>>>>>>>> java.util.Observer and Observable, and removed the 
>>>>>>>>>>> deprecation annotations. The only thing needed for the rest 
>>>>>>>>>>> of the code is to make sure we import these; I've done this 
>>>>>>>>>>> for three arbitrarily selected classes just to show what the 
>>>>>>>>>>> change would typically look like. Here's the mock-up:
>>>>>>>>>>>
>>>>>>>>>>> http://cr.openjdk.java.net/~ihse/hotspot-agent-observer/webrev.01 
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Let me know what you think.
>>>>>>>>>>>
>>>>>>>>>>> /Magnus
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>
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