We don't need jdk.internal.ref.Cleaner any more
chris.hegarty at oracle.com
Tue Feb 9 13:35:19 UTC 2016
On 08/02/16 10:58, Peter Levart wrote:
> On 02/08/2016 10:33 AM, Chris Hegarty wrote:
>> On 8 Feb 2016, at 06:27, Alan Bateman<Alan.Bateman at oracle.com> wrote:
>>> On 07/02/2016 22:20, Peter Levart wrote:
>>>> If the decision to remove sun.misc.Cleaner was partly influenced by the desire to maintain just 2 instead of 3 Cleaner(s), then my proposal to migrate JDK code to the public API might enable Oracle to reconsider keeping sun.misc.Cleaner.
>>> The main issue driving this is the design principles that we have listed in JEP 200. We don't want a standard module (java.base in this case) exporting a non-standard API. This means surgery to jettison the sun.misc package from java.base and move it to its own module (jdk.unsupported is the proposal in JEP 260). This is painful of course but we are at least in good shape for the most critical internal API, sun.misc.Unsafe.
>>> For sun.misc.Cleaner then the original proposal was for it to be a critical internal API too but it become clear that changing the type of internal/private fields in the NIO buffer and channel classes would break libraries that have been hacking into those fields. If they are changing away then there seems little motive to keep sun.misc.Cleaner so Chris moved into into jdk.internal.ref for now. As to whether we even need to keep jdk.internal.ref.Cleaner then I think the only remaining question was whether the special handling of Cleaner in the Reference implementation was worth it or not. It may not be, in which case your current proposal to just remove seems right.
>> Alan’s summary of the situation is spot on.
>> Before moving sun.misc.Cleaner to jdk.internal.ref, I did enquire if it would be
>> possible to just remove it and use the new public Cleaner, but I got feedback
>> that there were some issues with failing NIO tests ( it appeared that Cleaners
>> were not running as quickly as possible ). I didn’t look further into that at the
>> time, since the VM still had special knowledge of these cleaners, but as you
>> say this is now removed. It is probably a good time to revisit this.
> Hi Chris,
> Are you referring to the following test:
> test/java/nio/Buffer/DirectBufferAllocTest.java ?
> This test was written specifically for the following issue:
> ...which exercises multi-threaded allocation of direct buffers. Even
> sun.misc.Cleaner was not quick enough to promptly deallocate them, so
> allocation path was patched to help ReferenceHandler thread while
> re-attempting to allocate new direct buffers. Transitioning to
> java.lang.ref.Cleaner which uses additional thread to process
> Cleanable(s), direct-buffer allocation path must help the Cleaner thread
> too. See:
Ah, I was not aware of this. So additional threads attempting to
allocate already help out with cleaning. So moving away from the
ReferenceHandler Thread is not such a big deal as I was thinking.
> ...for the place where this is performed...
I did look through your changes and I think they are good. I'd like
to spend a little more time on the details.
> Regards, Peter
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