8307483: New micros for j.u.c.LockSupport by ericcaspole · Pull Request #13815 · openjdk/jdk

ericcaspole · 2023-05-04T20:17:11Z

These micros were developed while investigating JDK-8305670 by myself and Sergey Kuksenko. The order of thread creation was important in that bug, so there are 2 JMH for creating sleepers before and after the worker threads.

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JDK-8307483: New micros for j.u.c.LockSupport

Reviewers

Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to 4a486cfd
Claes Redestad (@cl4es - Reviewer) ⚠️ Review applies to 4a486cfd

Contributors

Sergey Kuksenko <skuksenko@openjdk.org>

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/13815/head:pull/13815
$ git checkout pull/13815

Update a local copy of the PR:
$ git checkout pull/13815
$ git pull https://git.openjdk.org/jdk.git pull/13815/head

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Checkout this PR locally:
$ git pr checkout 13815

View PR using the GUI difftool:
$ git pr show -t 13815

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https://git.openjdk.org/jdk/pull/13815.diff

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ericcaspole · 2023-05-04T20:17:37Z

/contributor add skuksenko

bridgekeeper · 2023-05-04T20:17:56Z

👋 Welcome back ecaspole! 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.

openjdk · 2023-05-04T20:19:43Z

@ericcaspole
Contributor Sergey Kuksenko <skuksenko@openjdk.org> successfully added.

openjdk · 2023-05-04T20:21:02Z

@ericcaspole The following label will be automatically applied to this pull request:

core-libs

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2023-05-04T20:25:41Z

Webrevs

AlanBateman · 2023-05-05T14:31:29Z

test/micro/org/openjdk/bench/java/util/concurrent/UnparkBenchSleepersAfter.java

+        @Override
+        public void run() {
+            my_thread = Thread.currentThread();
+            while (!done) {


You might want to re-check IdleThread. From a quick look I would have expected "done" to be volatile. Also "my_thread" as it is set in the run with plain access.

Yes done must be volatile. Surprised this even worked as expected.

Same as we saw with isAlive before: LockSupport.park implicitly provides a compiler barrier. This done should be at least "opaque" to carry the same effect.

Yes, park() and unpark() having release and acquire semantics is not documented here, and the documentation for LockSupport explicitly says "Reliable usage requires the use of volatile (or atomic) variables to control when to park or unpark. Orderings of calls to these methods are maintained with respect to volatile variable accesses, but not necessarily non-volatile variable accesses."

Irrespective of park/unpark barriers, the JIT should have hoisted done and rewritten as:

if (!done) { while(true) { ... } }

Well I guess the park/unpark barriers prevented that.

shipilev

Cursory style reviews.

test/micro/org/openjdk/bench/java/util/concurrent/UnparkBenchSleepersAfter.java

shipilev · 2023-05-08T09:20:40Z

test/micro/org/openjdk/bench/java/util/concurrent/UnparkBenchSleepersAfter.java

+        for(int i=0; i < idle_threads.length; i++) {
+            new Thread(idle_threads[i] = new IdleThread()).start();
+        }


These idleThreads are not actually Thread-s, they are Runnable-s.

Suggested change

for(int i=0; i < idle_threads.length; i++) {

new Thread(idle_threads[i] = new IdleThread()).start();

}

for(int i = 0; i < idles; i++) {

Runnable r = new IdleRunnable();

idleRunnables[i] = r;

new Thread(r).start();

}

test/micro/org/openjdk/bench/java/util/concurrent/UnparkBenchSleepersAfter.java

shipilev · 2023-05-08T09:21:54Z

test/micro/org/openjdk/bench/java/util/concurrent/UnparkBenchSleepersAfter.java

+        @Override
+        public void run() {
+            my_thread = Thread.currentThread();
+            while (!done) {


Same as we saw with isAlive before: LockSupport.park implicitly provides a compiler barrier. This done should be at least "opaque" to carry the same effect.

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

ericcaspole · 2023-05-16T14:36:05Z

I think I fixed all the commented items, could anyone look?

shipilev

Looks okay, with a few remaining nits.

test/micro/org/openjdk/bench/java/util/concurrent/UnparkBenchSleepersBefore.java

test/micro/org/openjdk/bench/java/util/concurrent/UnparkBenchSleepersAfter.java

openjdk · 2023-05-17T10:26:22Z

@ericcaspole 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:

8307483: New micros for j.u.c.LockSupport

Co-authored-by: Sergey Kuksenko <skuksenko@openjdk.org>
Reviewed-by: shade, redestad

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 204 new commits pushed to the master branch:

6d4782b: 8307976: (fs) Files.createDirectories(dir) returns dir::toAbsolutePath instead of dir
f57c783: 8308239: Tighten up accessibility of nested classes in java.lang.invoke
64f6681: 8308246: PPC64le build broken after JDK-8304913
5763be7: 8307326: Package jdk.internal.classfile.java.lang.constant become obsolete
c7951cf: 8306304: Fix xlc17 clang warnings in ppc and aix code
285c833: 8308043: Deadlock in TestCSLocker.java due to blocking GC while allocating
1a6f981: 8308185: Update Http2TestServerConnection to use SSLSocket.startHandshake()
b300e73: 8308088: Improve class check in CollectedHeap::is_oop
e34ecc9: 8296469: Instrument VMError::report with reentrant iteration step for register and stack printing
5a92aae: 8308156: VerifyCACerts.java misses blank in error output
... and 194 more: https://git.openjdk.org/jdk/compare/a87262efb2c0f5ed1773533d69d7d2091eba1462...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.

cl4es

LGTM with @shipilev's suggestions

Apply Aleksey's suggestions of May 17 Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

ericcaspole · 2023-05-17T20:38:30Z

/integrate

Thanks Claes and Aleksey!

openjdk · 2023-05-17T20:39:37Z

Going to push as commit 6073edf.
Since your change was applied there have been 207 commits pushed to the master branch:

2409448: 8307365: JvmtiStressModule hit SIGSEGV in JvmtiEventControllerPrivate::recompute_thread_enabled
950c5df: 8307299: Move more DnD tests to open
8bedf2e: 8308292: Problemlist vmTestbase/nsk/jvmti/AttachOnDemand/attach020/TestDescription.java
6d4782b: 8307976: (fs) Files.createDirectories(dir) returns dir::toAbsolutePath instead of dir
f57c783: 8308239: Tighten up accessibility of nested classes in java.lang.invoke
64f6681: 8308246: PPC64le build broken after JDK-8304913
5763be7: 8307326: Package jdk.internal.classfile.java.lang.constant become obsolete
c7951cf: 8306304: Fix xlc17 clang warnings in ppc and aix code
285c833: 8308043: Deadlock in TestCSLocker.java due to blocking GC while allocating
1a6f981: 8308185: Update Http2TestServerConnection to use SSLSocket.startHandshake()
... and 197 more: https://git.openjdk.org/jdk/compare/a87262efb2c0f5ed1773533d69d7d2091eba1462...master

Your commit was automatically rebased without conflicts.

openjdk · 2023-05-17T20:39:53Z

@ericcaspole Pushed as commit 6073edf.

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

8307483: New micros for j.u.c.LockSupport

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openjdk bot added the rfr Pull request is ready for review label May 4, 2023

openjdk bot added the core-libs core-libs-dev@openjdk.org label May 4, 2023

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ericcaspole and others added 2 commits May 9, 2023 13:25

Apply Aleksey's suggestions from code review

96caa77

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

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openjdk bot added the ready Pull request is ready to be integrated label May 17, 2023

cl4es approved these changes May 17, 2023

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Apply Aleksey's suggestions of May 17 Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

openjdk bot added the integrated Pull request has been integrated label May 17, 2023

openjdk bot closed this May 17, 2023

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels May 17, 2023

-        for(int i=0; i < idle_threads.length; i++) {
-            new Thread(idle_threads[i] = new IdleThread()).start();
-        }
+        for(int i = 0; i < idles; i++) {
+            Runnable r = new IdleRunnable();
+            idleRunnables[i] = r;
+            new Thread(r).start();
+        }

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