Discussion about fixing deprecation in jdk.hotspot.agent
Chris Plummer
chris.plummer at oracle.com
Wed Apr 1 20:01:15 UTC 2020
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.
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
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
>>>
>
More information about the serviceability-dev
mailing list