Bug ID: JDK-8221102 Allow GC threads to participate in threads claiming protocol

JDK-8221102 : Allow GC threads to participate in threads claiming protocol

Type: Bug
Component: hotspot
Sub-Component: gc
Affected Version: 13

Priority: P2
Status: Closed
Resolution: Fixed
OS: generic
CPU: generic

Submitted: 2019-03-19
Updated: 2019-08-08
Resolved: 2019-04-02

Versions (Unresolved/Resolved/Fixed)

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Resolved: Release in which this issue/RFE has been resolved.
Fixed : Release in which this issue/RFE has been fixed. The release containing this fix may be available for download as an Early Access Release or a General Availability Release.

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JDK 13
13 b15Fixed

Related Reports

Blocks :	JDK-8221435 - Shenandoah should not mark through weak roots
Relates :	JDK-8221785 - Add parallel threads_do variant for all threads
Relates :	JDK-8219613 - Use NonJavaThread PtrQueues
Relates :	JDK-8221516 - fatal error: Thread SATB queue has an unexpected active state

Sub Tasks

JDK-8221688 :	Quarantine Shenandoah string dedup tests - Resolved
JDK-8221875 :	Unquarantine Shenandoah string dedup tests - Resolved

Description

JDK-8219613 introduced SATB queues for NonJavaThreads. In Shenandoah (and likely G1) the StringDedupThread needs SATB queues. Also, in Shenandoah, all threads' SATB queues get flushed at end of marking using the thread claiming protocol. Currently, only Java threads and the VMThread participate in this, which means that the StringDedupThread will not have its SATB queue flushed at the end.
This change is proposing a mechanism to allow (some) GC threads to participate in thread claiming.

Comments

In fact, it seems very dangerous to do 'manual' claiming, e.g. do thread->claim_oops_do() in a ThreadClosure that is called via Threads::threads_do(). The usual thread claiming only does Java threads and VM thread, and only verifies those. Any other thread would not reliably claim.

19-03-2019