Bug ID: JDK-8175797 (ref) Reference::enqueue method should clear the reference object before enqueuing

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JDK 10	JDK 8	JDK 9	Other
10Fixed	8u351Fixed	9 b161Fixed	openjdk8u352Fixed

Soft, weak, and phantom references are automatically-cleared references (see JDK-8071507).   The referent is cleared before the reference object is enqueued.

The `enqueue` method should behave the same and it should clear the reference before enqueuing it to the registered queue.

Surveying the existing usage of this enqueue method, it's a common pattern that Reference::clear is called before or after enqueuing.

JDK 8u Fix Request: This fix is required for compliance with Java SE 8 Maintenance Release 4: https://jcp.org/en/jsr/detail?id=337
12-08-2022
A pull request was submitted for review. URL: https://git.openjdk.org/jdk8u-dev/pull/99 Date: 2022-08-11 19:12:23 +0000
11-08-2022
A pull request was submitted for review. URL: https://git.openjdk.java.net/jdk8u-ri/pull/5 Date: 2022-04-20 00:15:58 +0000
20-04-2022
URL: http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/bc1bf2be03bc User: lana Date: 2017-03-15 14:49:32 +0000
15-03-2017
URL: http://hg.openjdk.java.net/jdk9/dev/jdk/rev/bc1bf2be03bc User: mchung Date: 2017-03-09 15:42:25 +0000
09-03-2017
FC Extension Request The proposed spec and implementation is low risk [1] as a follow-up spec change per JDK-8071507. I have looked at the existing usage of this enqueue method from Maven artifacts shows that Reference::clear is called either before or after calling Reference::enqueue as a pair. In addition, existing code polls the enqueued reference from a ReferenceQueue that is expected that the reference object may have been cleared. We expect that the compatibility risk should be low and existing applications being impacted by this change should be very low. `jdk.ref.disableClearBeforeEnqueue` system property is introduced to disable the new behavior in case an existing application is impacted by this change and need time to fix their code. The fix is ready and I expect to integrate by 3/15 or earlier. [1] http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8175797/webrev.00/index.html
08-03-2017

CSR :	CCC-8175797 - (ref) Reference::enqueue should clear the reference object before enqueuing
Relates :	JDK-8178832 - (ref) jdk.lang.ref.disableClearBeforeEnqueue property is ignored
Relates :	JDK-8193780 - (ref) Remove the undocumented "jdk.lang.ref.disableClearBeforeEnqueue" system property
Relates :	JDK-8203028 - Simplify reference processing in light of JDK-8175797
Relates :	JDK-8071507 - (ref) Clear phantom reference as soft and weak references do
Relates :	JDK-8215985 - ZGC: Simplify reference processing in light of JDK-8175797