We don't need jdk.internal.ref.Cleaner any more
peter.levart at gmail.com
Mon Feb 8 10:58:34 UTC 2016
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.
Are you referring to the following test:
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
...for the place where this is performed...
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