8253241: Update comment on java_suspend_self_with_safepoint_check() #225

reinrich · 2020-09-17T13:57:04Z

After JDK-8252414 the safepoint/handshake code does not take _suspend_flags into accout anymore in its assessment if a thread is safepoint/handshake safe. This change updates the comment on JavaThread::java_suspend_self_with_safepoint_check().

I have (not yet) fixed the line breaks (fill-paragraph in emacs lingo) for a clearer diff.

Also I could inline the (*) footnote.

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Issue

JDK-8253241: Update comment on java_suspend_self_with_safepoint_check()

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Daniel D. Daugherty (@dcubed-ojdk - Reviewer) ⚠️ Review applies to 177221c
David Holmes (@dholmes-ora - Reviewer)

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$ git fetch https://git.openjdk.java.net/jdk pull/225/head:pull/225
$ git checkout pull/225

bridgekeeper · 2020-09-17T13:58:52Z

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openjdk · 2020-09-17T14:00:31Z

@reinrich The following label will be automatically applied to this pull request: hotspot-runtime.

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mlbridge · 2020-09-17T14:06:16Z

Webrevs

01: Full - Incremental (e1ac0b9)
00: Full (177221c)

dcubed-ojdk

The updated wording in the comment looks good to me.

I still get a headache when thinking about the associated
suspend/resume races, but that's my problem and not yours.

openjdk · 2020-09-18T21:50:18Z

@reinrich This change now passes all automated pre-integration checks. In addition to the automated checks, the change must also fulfill all project specific requirements

After integration, the commit message will be:

8253241: Update comment on java_suspend_self_with_safepoint_check()

Reviewed-by: dcubed, dholmes

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Since the source branch of this PR was last updated there have been 79 commits pushed to the master branch:

bd67975: 8253349: Remove unimplemented SharedRuntime::native_method_throw_unsupported_operation_exception_entry
bddb822: 8253240: No javadoc for DecimalFormatSymbols.hashCode()
c68a31d: 8253499: Problem list runtime/cds/DeterministicDump.java
93a2018: 8252195: AWT Accessibility API nested classes rely on default constructors
426c904: 8253392: remove PhaseCCP_DCE declaration
65af837: 8253496: [BACKOUT] JDK-8253208 Move CDS related code to a separate class
581f0f2: 8253493: Shenandoah: Remove ShenandoahSerialRoot definition
7b86012: 8253492: Miss comma after second copyright year in FDBigInteger.java
0f26ab1: 8252518: cache result of CompilerToVM.getComponentType
c1df13b: 8253208: Move CDS related code to a separate class
... and 69 more: https://git.openjdk.java.net/jdk/compare/ce93cbce77e1f4baa52676826c8ae27d474360b6...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid automatic rebasing, please merge master into your branch, and then specify the current head hash when integrating, like this: /integrate bd6797543f6812d0b1cc5d45d40aec82674040e8.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

dcubed-ojdk · 2020-09-18T21:52:31Z

Please wait for @dholmes-ora to review this change.

reinrich · 2020-09-19T21:18:58Z

The updated wording in the comment looks good to me.

Thanks for looking over it.

I still get a headache when thinking about the associated
suspend/resume races, but that's my problem and not yours.

I'd think the suspend/resume implementation could be simplified if the suspender would always direct handshake the suspendee. JavaThread::is_ext_suspend_completed() could be removed then. Likewise the suspend equivalent optimization. And I would not expect an impact on performance by doing it.

reinrich · 2020-09-19T21:19:26Z

Please wait for @dholmes-ora to review this change.

Sure.

dholmes-ora · 2020-09-21T04:12:39Z

src/hotspot/share/runtime/thread.cpp

+// The correct thread state of a suspended thread is _thread_blocked. With that state
+// safepoint/handshake code will count it as safepoint/handshake safe. Also it allows
+// another thread to continue if it is waiting in is_ext_suspend_completed() for this
+// thread to change state from _thread_in_native_trans to the target state.


The revised wording doesn't really convey the situation to me. We have to set the thread-state to _thread_blocked so that a thread waiting in _is_ext_suspend_completed can proceed (there is no generic "target" state - it must be _thread_blocked). I would simplify and rephrase as follows:

"We have to set the thread state directly to _thread_blocked so that it will be seen to be safepoint/handshake safe whilst suspended. This is also necessary to allow a thread in is_ext_suspend_completed, that observed the _thread_in_native_trans state, to proceed."

Ok, I will use your version.

dholmes-ora

LGTM! :) Thanks

reinrich · 2020-09-22T09:12:18Z

Thanks :)
I'll integrate this after another 24h.

reinrich · 2020-09-23T07:15:59Z

/integrate

openjdk · 2020-09-23T07:17:42Z

@reinrich Since your change was applied there have been 79 commits pushed to the master branch:

bd67975: 8253349: Remove unimplemented SharedRuntime::native_method_throw_unsupported_operation_exception_entry
bddb822: 8253240: No javadoc for DecimalFormatSymbols.hashCode()
c68a31d: 8253499: Problem list runtime/cds/DeterministicDump.java
93a2018: 8252195: AWT Accessibility API nested classes rely on default constructors
426c904: 8253392: remove PhaseCCP_DCE declaration
65af837: 8253496: [BACKOUT] JDK-8253208 Move CDS related code to a separate class
581f0f2: 8253493: Shenandoah: Remove ShenandoahSerialRoot definition
7b86012: 8253492: Miss comma after second copyright year in FDBigInteger.java
0f26ab1: 8252518: cache result of CompilerToVM.getComponentType
c1df13b: 8253208: Move CDS related code to a separate class
... and 69 more: https://git.openjdk.java.net/jdk/compare/ce93cbce77e1f4baa52676826c8ae27d474360b6...master

Your commit was automatically rebased without conflicts.

Pushed as commit 226faa5.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8253241: Update comment on java_suspend_self_with_safepoint_check()

177221c

openjdk bot added the hotspot-runtime hotspot-runtime-dev@openjdk.org label Sep 17, 2020

reinrich marked this pull request as ready for review September 17, 2020 14:01

openjdk bot added the rfr Pull request is ready for review label Sep 17, 2020

dcubed-ojdk approved these changes Sep 18, 2020

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dholmes-ora reviewed Sep 21, 2020

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openjdk bot closed this Sep 23, 2020

openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated labels Sep 23, 2020

openjdk bot removed the rfr Pull request is ready for review label Sep 23, 2020

reinrich deleted the JDK-8253241 branch September 23, 2020 07:22

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