Discussion about fixing deprecation in jdk.hotspot.agent

[coleen.phillimore at oracle.com]

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
>>
>