8276824: refactor Thread::is_JavaThread_protected #6315

dcubed-ojdk · 2021-11-09T15:07:58Z

Refactor Thread::is_JavaThread_protected(const JavaThread* p, bool checkTLHOnly)
into: bool Thread::is_JavaThread_protected(const JavaThread* p)
and: Thread::is_JavaThread_protected_by_TLH(const JavaThread* p).
Also change callers that passed checkTLHOnly == true into calls to
Thread::is_JavaThread_protected_by_TLH(const JavaThread* p).

This refactoring is being tested with Mach5 Tier[1-3] (in process).

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Issue

JDK-8276824: refactor Thread::is_JavaThread_protected

Reviewers

Coleen Phillimore (@coleenp - Reviewer)
Robbin Ehn (@robehn - Reviewer) ⚠️ Review applies to 02aefa6
David Holmes (@dholmes-ora - Reviewer)

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bridgekeeper · 2021-11-09T15:08:10Z

👋 Welcome back dcubed! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

dcubed-ojdk · 2021-11-09T15:08:33Z

/label add hotspot-runtime

openjdk · 2021-11-09T15:09:59Z

@dcubed-ojdk
The hotspot-runtime label was successfully added.

dcubed-ojdk · 2021-11-09T15:17:08Z

@coleenp, @dholmes-ora and @robehn - since the three of you were involved in the
review for: "JDK-8249004 Reduce ThreadsListHandle overhead in relation to direct handshakes"
I would like you to chime in on this refactoring. Thanks!

Advantages to this version (from my POV):

Thread::is_JavaThread_protected() is smaller and simpler without the flag.
Thread::is_JavaThread_protected_by_TLH() is very small and straight forward.

Disadvantages to this version (from my POV):

current_thread is materialized in both functions instead of just once.

@dholmes-ora says that materializing current_thread is no longer as expensive as
it used to be so I'm not worried about the disadvantage anymore.

mlbridge · 2021-11-09T15:25:45Z

Webrevs

01: Full - Incremental (ea536662)
00: Full (02aefa66)

coleenp

Thank you for this refactoring. A small suggestion, we'll see if it's popular or not.

coleenp · 2021-11-09T15:29:44Z

src/hotspot/share/runtime/thread.cpp

+// Is the target JavaThread protected by a ThreadsListHandle (TLH) associated
+// with the calling Thread?
+//
+bool Thread::is_JavaThread_protected_by_TLH(const JavaThread* p) {


I think you could pass JavaThread* current as the first parameter here. The naming will help to keep it straight and make this an assert(current == JavaThread::current() if this is deemed to be expensive.
At the callsites below, it would make it obvious that "this" isn't meant to be the current thread (and calling Thread::current() inside a (tbd) assert would make it clear which thread is which.

With this handshake code I continuously am trying to figure out which thread is current vs. target.

I'm not fond of passing the current thread in as a parameter because that could
make folks think that these functions can be called on any Thread*. They must
be called in the context of the current thread which is also why they are static.
I would like to rename the p parameter to target and I could add /*target*/
to the call sites to make things more clear.

openjdk · 2021-11-09T15:30:47Z

@dcubed-ojdk This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8276824: refactor Thread::is_JavaThread_protected

Reviewed-by: coleenp, rehn, dholmes

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 23 new commits pushed to the master branch:

e91e9d8: 8276721: G1: Refine G1EvacFailureObjectsSet::iterate
8822d41: 8274736: Concurrent read/close of SSLSockets causes SSLSessions to be invalidated unnecessarily
c1e41fe: 8276842: G1: Only calculate size in bytes from words when needed
c8b0ee6: 8276833: G1: Make G1EvacFailureRegions::par_iterate const
0699220: 8268882: C2: assert(n->outcnt() != 0 || C->top() == n || n->is_Proj()) failed: No dead instructions after post-alloc
d7012fb: 8276880: Remove java/lang/RuntimeTests/exec/ExecWithDir as unnecessary
f9024d0: 8230130: javadoc search result dialog shows cut off headers for long results
055de6f: 8223358: Incorrect HTML structure in annotation pages
a60e912: 8198626: java/awt/KeyboardFocusmanager/TypeAhead/TestDialogTypeAhead.html fails on mac
dde959d: 8276808: java/nio/channels/Channels/TransferTo.java timed out
... and 13 more: https://git.openjdk.java.net/jdk/compare/905e3e88137d46f90de7034e9fc324e97af873a6...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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

dcubed-ojdk · 2021-11-09T16:27:08Z

I've pushed changes to clarify the target thread parameter.

dcubed-ojdk · 2021-11-09T16:27:46Z

@coleenp and @robehn - Thanks for reviewing.

coleenp

Ok, thanks!

dcubed-ojdk · 2021-11-09T16:40:46Z

@robehn - are you okay with the comment updates?

dholmes-ora

Hi Dan,

I'm okay with the changes as-is but also would not object to passing the current thread to avoid manifesting it - we do that a lot in other parts of the VM.

One (multi-place) nit below.

Thanks,
David

dholmes-ora · 2021-11-10T02:54:07Z

src/hotspot/share/runtime/thread.cpp

@@ -1750,13 +1761,13 @@ void JavaThread::send_thread_stop(oop java_throwable)  {
 //   - Target thread will not enter any new monitors.
 //
 bool JavaThread::java_suspend() {
-  guarantee(Thread::is_JavaThread_protected(this, /* checkTLHOnly */ true),
+  guarantee(Thread::is_JavaThread_protected_by_TLH(/* target */ this),


Nit: there's no need to comment a single argument.

I added the comment due to this comment from @coleenp:

At the callsites below, it would make it obvious that "this" isn't meant to be the current thread (and calling Thread::current() inside a (tbd) assert would make it clear which thread is which.

I read @coleenp's comment as meaning that the uncommented this could be made more
obvious so I'm going to leave those two /* target */ comments for clarity.

dcubed-ojdk · 2021-11-12T19:04:51Z

@dholmes-ora - Thanks for re-review! I think we're good to go on this cleanup.

/integrate

openjdk · 2021-11-12T19:06:15Z

Going to push as commit 176d21d.
Since your change was applied there have been 69 commits pushed to the master branch:

74f3e69: 8277071: [BACKOUT] JDK-8276743 Make openjdk build Zip Archive generation "reproducible"
b85500e: 8276123: ZipFile::getEntry will not return a file entry when there is a directory entry of the same name within a Zip File
0d2980c: 8258192: Obsolete the CriticalJNINatives flag
5a2452c: 8274835: Remove unnecessary castings in java.base
3b2585c: 8276658: Clean up JNI local handles code
aeba653: 8276743: Make openjdk build Zip Archive generation "reproducible"
51a5731: 8277016: Use blessed modifier order in jdk.httpserver
c4b4432: 8277012: Use blessed modifier order in src/utils
13deb38: 8276848: sun.net.httpserver.simpleserver.CommandLinePositiveTest: test does not specify port
710f496: 8273277: C2: Move conditional negation into rc_predicate
... and 59 more: https://git.openjdk.java.net/jdk/compare/905e3e88137d46f90de7034e9fc324e97af873a6...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-11-12T19:06:37Z

@dcubed-ojdk Pushed as commit 176d21d.

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

8276824.cr0.patch

02aefa6

openjdk bot added the hotspot-runtime label Nov 9, 2021

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clarify the target thread parameter.

ea53666

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dcubed-ojdk deleted the JDK-8276824 branch Nov 12, 2021

8276824: refactor Thread::is_JavaThread_protected #6315

8276824: refactor Thread::is_JavaThread_protected #6315

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8276824: refactor Thread::is_JavaThread_protected #6315

8276824: refactor Thread::is_JavaThread_protected #6315

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dcubed-ojdk commented Nov 9, 2021 • edited by openjdk[bot] bot

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