Peter,
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.bate...@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.
-Chris.
Hi Chris,
Are you referring to the following test:
test/java/nio/Buffer/DirectBufferAllocTest.java ?
This test was written specifically for the following issue:
https://bugs.openjdk.java.net/browse/JDK-6857566
...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.
http://cr.openjdk.java.net/~plevart/jdk9-dev/removeInternalCleaner/webrev.02/src/java.base/share/classes/java/nio/Bits.java.sdiff.html
...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.
-Chris.
Regards, Peter
