8256306: ObjectMonitor::_contentions field should not be 'jint' by coleenp · Pull Request #3980 · openjdk/jdk

coleenp · 2021-05-11T15:01:18Z

I changed the _contentions and _waiters fields from jint to int and ran tests tier1-3. Tested tier1 with linux, mac, windows platforms. Also changed the _previous_owner_tid to unintptr_t from jlong, since that's what the cast did.

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Issue

JDK-8256306: ObjectMonitor::_contentions field should not be 'jint'

Reviewers

David Holmes (@dholmes-ora - Reviewer)
Thomas Stuefe (@tstuefe - Reviewer) ⚠️ Review applies to 7c28790
Daniel D. Daugherty (@dcubed-ojdk - Reviewer)

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bridgekeeper · 2021-05-11T15:04:18Z

👋 Welcome back coleenp! 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 · 2021-05-11T15:07:08Z

@coleenp The following labels will be automatically applied to this pull request:

hotspot-runtime
serviceability

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

bridgekeeper · 2021-06-08T15:58:48Z

@coleenp This pull request has been inactive for more than 8 weeks and will be automatically closed if another 8 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

mlbridge · 2021-06-21T15:16:40Z

Webrevs

01: Full - Incremental (07138653)
00: Full (7c287908)

dholmes-ora

Looks fine apart from use of INT32_MIN instead of INT_MIN.

Thanks,
David

src/hotspot/share/runtime/objectMonitor.cpp

dholmes-ora · 2021-06-21T23:56:36Z

src/hotspot/share/runtime/objectMonitor.cpp

    // Make a zero contentions field negative to force any contending threads
    // to retry. This is the second part of the async deflation dance.
-    if (Atomic::cmpxchg(&_contentions, (jint)0, -max_jint) != 0) {
+    if (Atomic::cmpxchg(&_contentions, (int)0, INT32_MIN) != 0) {


INT_MIN

Do we really need the cast on 0?

The original cast of (jint)0 was to get the right cmpxchg() selected.
I think that with the switch to INT32_MIN, a regular 0 instead of (int)0
should compile.

Yes, changing to INT_MIN is more correct and I don't need the cast to int now for zero. Recompiling on all platforms, including the picky ones for verification. Thanks!

openjdk · 2021-06-22T00:00:10Z

@coleenp 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:

8256306: ObjectMonitor::_contentions field should not be 'jint'

Reviewed-by: dholmes, stuefe, dcubed

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 13 new commits pushed to the master branch:

0c693e2: 8268290: Improve LockFreeQueue<> utility
33c23a1: 8264941: Remove CodeCache::mark_for_evol_deoptimization() method
18a1dd2: 8269031: linux x86_64 check for binutils 2.25 or higher after 8265783
2e639dd: 8267657: Add missing PrintC1Statistics before incrementing counters
1f0ea7c: 8268857: Merge VM_PrintJNI and VM_PrintThreads and remove the unused field 'is_deadlock' of DeadlockCycle
1a81815: 8269077: TestSystemGC uses "require vm.gc.G1" for large pages subtest
0458113: Merge
d3ad8cd: 8268672: C2: assert(!loop->is_member(u_loop)) failed: can be in outer loop or out of both loops only
f25e719: 8268717: Upstream: 8268673: Stack walk across optimized entry frame on fresh native thread fails
22ebd19: 8268362: [REDO] C2 crash when compile negative Arrays.copyOf length after loop
... and 3 more: https://git.openjdk.java.net/jdk/compare/cd20c01942dd8559a31e51ef2a595c6eba44b8ad...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.

tstuefe

LGTM

tstuefe · 2021-06-22T04:09:48Z

src/hotspot/share/runtime/objectMonitor.hpp

+    intptr_t ret_code = intptr_t(_waiters) | intptr_t(_cxq) | intptr_t(_EntryList);
+    int cnts = contentions(); // read once
+    if (cnts > 0) {
+      ret_code |= intptr_t(cnts);


I know it has nothing to do with your patch, but I am just curious. IIUC this is a strange way of saying "if A!=0 || B!=0 || C!=0..." . Is this for performance reasons? Also, why the "if (cnts > 0)", would that not be superfluous?

I think this code exists like this from when is_busy returned an uintptr_t. It should be nicely rewritten with if != 0s now and likely would have better performance. I won't do it with this change because these fields are volatile and I think should have Atomic::loads, which would lead to a lot of discussion that should happen independently. I'll file an RFE.

dcubed-ojdk · 2021-06-22T15:43:34Z

src/hotspot/share/runtime/objectMonitor.cpp

    // Make a zero contentions field negative to force any contending threads
    // to retry. This is the second part of the async deflation dance.
-    if (Atomic::cmpxchg(&_contentions, (jint)0, -max_jint) != 0) {
+    if (Atomic::cmpxchg(&_contentions, (int)0, INT32_MIN) != 0) {


The original cast of (jint)0 was to get the right cmpxchg() selected.
I think that with the switch to INT32_MIN, a regular 0 instead of (int)0
should compile.

src/hotspot/share/runtime/objectMonitor.hpp

dcubed-ojdk

Re-reviewed v01 incremental. Thumbs up!

dholmes-ora

Looks good!

Good catch on the padding @dcubed-ojdk !

Thanks,
David

coleenp · 2021-06-23T14:25:59Z

Thank you David, Dan and Thomas. There are a few other jlongs hanging around in that file, but that's for another day.
/integrate

openjdk · 2021-06-23T14:27:37Z

Going to push as commit f3ba269.
Since your change was applied there have been 33 commits pushed to the master branch:

52d5d1b: 8269188: [BACKOUT] Remove CodeCache::mark_for_evol_deoptimization() method
f2e690e: 8268720: Unspecified checks on NameAndType constants should not be performed
2c29d79: 8269206: A small typo in comment in test/lib/sun/hotspot/WhiteBox.java
6237630: 8269120: Build failure with GCC 6.3.0 after JDK-8017163
a5e4307: 8269134: Remove sparsePRT.inline.hpp after JDK-8017163
17daf32: 8269138: Move typeArrayOop.inline.hpp include to vectorSupport.cpp
36d82b6: 8268858: Determine register pressure automatically by the number of available registers for allocation
ae3eedc: 8268727: Remove unused slowpath locking method in OptoRuntime
cd678a3: 8268368: Adopt cast notation for JavaThread conversions
b6cfca8: Merge
... and 23 more: https://git.openjdk.java.net/jdk/compare/cd20c01942dd8559a31e51ef2a595c6eba44b8ad...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-06-23T14:27:54Z

@coleenp Pushed as commit f3ba269.

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

openjdk bot added serviceability serviceability-dev@openjdk.org hotspot-runtime hotspot-runtime-dev@openjdk.org labels May 11, 2021

coleenp force-pushed the jint branch from 10ceb67 to 8ee081c Compare June 16, 2021 21:38

8256306: ObjectMonitor::_contentions field should not be 'jint'

7c28790

coleenp force-pushed the jint branch from 8ee081c to 7c28790 Compare June 21, 2021 15:06

coleenp marked this pull request as ready for review June 21, 2021 15:11

openjdk bot added the rfr Pull request is ready for review label Jun 21, 2021

dholmes-ora approved these changes Jun 21, 2021

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openjdk bot added the ready Pull request is ready to be integrated label Jun 22, 2021

tstuefe approved these changes Jun 22, 2021

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dcubed-ojdk suggested changes Jun 22, 2021

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Fix INT32_MIN and cache padding.

0713865

dcubed-ojdk approved these changes Jun 22, 2021

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dholmes-ora approved these changes Jun 22, 2021

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openjdk bot closed this Jun 23, 2021

openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jun 23, 2021

coleenp deleted the jint branch June 23, 2021 14:32

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