RFR: JDK-8149925 We don't need jdk.internal.ref.Cleaner any more

[Kim Barrett]

> On Feb 17, 2016, at 4:06 AM, Peter Levart <peter.levart at gmail.com> wrote:
> 
> Hi Kim,
> 
> Thanks for looking into this. Answers inline…

Peter,

Thanks for the explanations.

> On 02/17/2016 01:20 AM, Kim Barrett wrote:
>>> However, I recall Roger saying there were existing tests that
>> failed when certain uses of sun.misc.Cleaner were replaced with
>> java.lang.ref.Cleaner. I don't remember the details, but maybe Roger
>> does.
> 
> If the failing test was the following:
> 
> java/nio/Buffer/DirectBufferAllocTest.java
> 
> ...then it has been taken care of (see Bits.java).

That looks familiar. And yes, I see what you did there, and I don't
think Roger's initial prototype testing did anything similar, so
indeed this is likely the failure he encountered.

Though I'm still inclined to object to that form of drainQueue (see
below).

>> I don't understand why CleanerImpl needs to be changed to public in
>> order to provide access to the new drainQueue. Wouldn't it be better
>> to add Cleaner.drainQueue?
> 
> An interesting idea. But I don't know if such functionality is generally useful enough to commit to it in a public API.

java.desktop:sun.java2d.Disposer.pollRemove seems to me to be
addressing an essentially similar requirement, with
java.desktop:sun.font.StrikeCache being the user of that API.

Of course, that's already got all the scaffolding for using phantom
references, and there's no need to rewrite it to use
java.lang.ref.Cleaner.  But maybe there are others like this?

In any case, I really dislike the approach of exposing the CleanerImpl
object to get at this functionality.

>> Some of the other changes here don't seem related to the problem at
>> hand. ...
> 
> One thing that this change unfortunately requires is to get rid of lambdas and method references in the implementation and dependencies of java.land.ref.Cleaner API, because it gets used early in the boot-up sequence when java.lang.invoke infrastructure is not ready yet.

Oh, right!  Bootstrapping issues!

> The alternative to CleanerCleanable is a no-op Runnable implementation passed to PhantomCleanableRef constructor. …

OK.  Now I understand.

> Making CleanerImpl implement Runnable …

I'd be fine with this if the CleanerImpl wasn't exposed as part of the
drainQueue functionality.

>> ------------------------------------------------------------------------------
>> src/java.base/share/classes/sun/nio/fs/NativeBuffer.java
>>   76     Cleaner.Cleanable cleanable() {
>>   77         return cleanable;
>>   78     }
>> 
>> [pre-existing, but if we're changing things anyway...]
>> 
>> I'm kind of surprised by an accessor function (both here and in the
>> original code) rather than a cleanup function.  Is there a use case
>> for anything other than buffer.cleanable().clean()?
> 
> It can't be, since both old Cleaner and new Cleanable have only got a single method - clean().

So this could be replaced with

  void clean() {
    cleanable.clean();
  }

To me, that seems better.

>> Similarly for the DirectBuffer interface.
> 
> This one is a critical method, used by various 3rd party softwares...

I want to cover my ears when people start talking about some of the
things that have done…  OK.