Bug ID: JDK-8133348 Reference.reachabilityFence

Type: Sub-task
Component: core-libs
Sub-Component: java.lang
Affected Version: 9

Priority: P4
Status: Resolved
Resolution: Fixed

Submitted: 2015-08-11
Updated: 2019-06-12
Resolved: 2015-12-14

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JDK 9
9 b103Fixed

This RFE covers the implementation of Fences.reachabilityFence, as suggested by Doug Lea.

Proof of concept, plus tests:
 http://cr.openjdk.java.net/~shade/8133348/

Notes from Vitaly on possible key performance issues with the current implementation approach: http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-December/020366.html http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-December/020367.html 1) current impl/prototype is purposely barred from inlining - this will be a compiler optimization fence, particularly bad in loops 2) the expected "try { ... use(r) ... } finally { reachabilityFence(r); }" idiom will significantly increase bytecode size, possibly impacting inlining. 3) what impact will this have, if any, on register allocation when a ref's lifetime is artificially extended without any "real" use. The thinking here is compiler should spill it and never reload, but it was unclear if it will do the right thing in its current form. Discussion thread on concurrency-interest: http://cs.oswego.edu/pipermail/concurrency-interest/2015-December/014609.html

14-12-2015

Blocks :	JDK-8145459 - Cleaner - use Reference.reachabilityFence
Duplicate :	JDK-8055183 - Decide whether this can be GCed
Relates :	JDK-8169605 - reachabilityFence needs to be optimized away by the JIT
Relates :	JDK-8177915 - Clarify Reference.reachabilityFence use
Relates :	JDK-8146090 - java/lang/ref/ReachabilityFenceTest.java fails with -XX:+DeoptimizeALot
Relates :	JDK-8055183 - Decide whether this can be GCed
Relates :	JDK-8130398 - Coalesce prolog and epilog for empty methods
Relates :	JDK-8225675 - Outdated citation of JLS in java.lang.ref.Reference