8255070: Shenandoah: Use single thread for concurrent CLD liveness test #777

zhengyu123 · 2020-10-20T23:48:58Z

Since the concurrent liveness test does not touch any oops, there is no point to use multi-thread for the task, they just duplicate the work.

Also, multi-thread version requires to acquire ClassLoaderGraph_lock early, which is deadlock prone.

Progress

Change must not contain extraneous whitespace
Commit message must refer to an issue
Change must be properly reviewed

Testing

	Linux x64	Windows x64	macOS x64
Build	✔️ (5/5 passed)	✔️ (2/2 passed)	✔️ (2/2 passed)
Test (tier1)	✔️ (9/9 passed)	✔️ (9/9 passed)	✔️ (9/9 passed)

Issue

JDK-8255070: Shenandoah: Use single thread for concurrent CLD liveness test

Reviewers

Roman Kennke (@rkennke - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/777/head:pull/777
$ git checkout pull/777

bridgekeeper · 2020-10-20T23:49:26Z

👋 Welcome back zgu! 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 · 2020-10-20T23:50:49Z

@zhengyu123 The following labels will be automatically applied to this pull request:

hotspot-gc
shenandoah

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.

mlbridge · 2020-10-20T23:54:17Z

Webrevs

AzeemJiva · 2020-10-21T00:04:09Z

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

@@ -1941,7 +1941,7 @@ class ShenandoahConcurrentWeakRootsEvacUpdateTask : public AbstractGangTask {
  ShenandoahVMWeakRoots<true /*concurrent*/> _vm_roots;

  // Roots related to concurrent class unloading
-  ShenandoahClassLoaderDataRoots<true /* concurrent */, false /* single thread*/>
+  ShenandoahClassLoaderDataRoots<true /* concurrent */, true /* single thread*/>


Should the first input be false?

No. It runs concurrently, so will need to acquire ClassLoaderGraph_lock.

rkennke · 2020-10-21T12:47:31Z

src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.inline.hpp

+      assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
+      assert(Thread::current()->is_VM_thread(), "Can only be done by VM thread");
+      ClassLoaderDataGraph::always_strong_cld_do(clds);
+    }
  } else if (_semaphore.try_acquire()) {


It looks to me that we do:
if (_semaphore.try_acquire()) {

in both branches now. Can this be reshaped to do try_acquire() and claim_all() outermost?

rkennke · 2020-10-21T12:49:35Z

src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.inline.hpp

+      assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
+      assert(Thread::current()->is_VM_thread(), "Can only be done by VM thread");
+      ClassLoaderDataGraph::cld_do(clds);
+    }
  } else if (_semaphore.try_acquire()) {


Same as above. Also, the only difference to above is cld_do() vs always_strong_cld_do(), with lots of identical boilerplate. Can this be refactored into a generic method that takes the final target method as argument?

Refactored and retested. Thanks for the suggestion.

rkennke

Also, I'd change the commit message to begin uppercase after Shenandoah: "Use..."

rkennke · 2020-10-21T15:39:35Z

src/hotspot/share/gc/shenandoah/shenandoahRootProcessor.inline.hpp

+      if (SINGLE_THREADED) ClassLoaderDataGraph_lock->lock();
+      f(clds);
+      if (SINGLE_THREADED) ClassLoaderDataGraph_lock->unlock();
+      _semaphore.claim_all();


Would it be nicer to write this as follows?
if (SINGLE_THREADED) {
MutexLocker ml(ClassLoaderDataGraph_lock);
f(clds);
} else {
f(clds);
}

rkennke

Looks good to me! Thank you!

openjdk · 2020-10-21T18:03:28Z

@zhengyu123 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:

8255070: Shenandoah: Use single thread for concurrent CLD liveness test

Reviewed-by: rkennke

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 86 new commits pushed to the master branch:

8d9e6d0: 8255041: Zero: remove old JSR 292 support leftovers
0efdde1: 8238669: Long.divideUnsigned is extremely slow for certain values (Needs to be Intrinsic)
365f19c: 8254790: SIGSEGV in string_indexof_char and stringL_indexof_char intrinsics
f813a28: 8254692: (se) Clarify the behaviour of the non-abstract SelectorProvider::inheritedChannel
c9269bf: 8255036: Shenandoah: Reset GC state for root verifier
839f01d: 8242068: Signed JAR support for RSASSA-PSS and EdDSA
e559bd2: 8254889: name_and_sig_as_C_string usages in frame coding without ResourceMark
da97ab5: 8253474: Javadoc clean up in HttpsExchange, HttpsParameters, and HttpsServer
7e26404: 8255000: C2: Unify IGVN processing when loop opts are over
27230fa: 8255026: C2: Miscellaneous cleanups in Compile and PhaseIdealLoop code
... and 76 more: https://git.openjdk.java.net/jdk/compare/4ffed326fa3969b8d984109d9fceb02c968f6b44...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.

zhengyu123 · 2020-10-21T19:43:05Z

/integrate

openjdk · 2020-10-21T19:47:43Z

@zhengyu123 Since your change was applied there have been 87 commits pushed to the master branch:

6020991: 8255068: [JVMCI] errors during compiler creation can be hidden
8d9e6d0: 8255041: Zero: remove old JSR 292 support leftovers
0efdde1: 8238669: Long.divideUnsigned is extremely slow for certain values (Needs to be Intrinsic)
365f19c: 8254790: SIGSEGV in string_indexof_char and stringL_indexof_char intrinsics
f813a28: 8254692: (se) Clarify the behaviour of the non-abstract SelectorProvider::inheritedChannel
c9269bf: 8255036: Shenandoah: Reset GC state for root verifier
839f01d: 8242068: Signed JAR support for RSASSA-PSS and EdDSA
e559bd2: 8254889: name_and_sig_as_C_string usages in frame coding without ResourceMark
da97ab5: 8253474: Javadoc clean up in HttpsExchange, HttpsParameters, and HttpsServer
7e26404: 8255000: C2: Unify IGVN processing when loop opts are over
... and 77 more: https://git.openjdk.java.net/jdk/compare/4ffed326fa3969b8d984109d9fceb02c968f6b44...master

Your commit was automatically rebased without conflicts.

Pushed as commit 615b759.

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

Zhengyu Gu added 2 commits October 20, 2020 16:48

8255070: Shenandoah: use single thread for concurrent CLD liveness test

f8c5be0

Fix include

5b69d7b

openjdk bot added the rfr Pull request is ready for review label Oct 20, 2020

openjdk bot added hotspot-gc hotspot-gc-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Oct 20, 2020

AzeemJiva reviewed Oct 21, 2020

View reviewed changes

rkennke reviewed Oct 21, 2020

View reviewed changes

zhengyu123 changed the title ~~8255070: Shenandoah: use single thread for concurrent CLD liveness test~~ 8255070: Shenandoah: Use single thread for concurrent CLD liveness test Oct 21, 2020

Reduce duplicated code

c46f8d3

rkennke reviewed Oct 21, 2020

View reviewed changes

Replaced naked lock/unlock with MutexLocker

f2dded6

rkennke approved these changes Oct 21, 2020

View reviewed changes

openjdk bot added the ready Pull request is ready to be integrated label Oct 21, 2020

openjdk bot closed this Oct 21, 2020

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 Oct 21, 2020

zhengyu123 deleted the JDK-8255070-CLD-liveness branch February 11, 2021 14:59

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

8255070: Shenandoah: Use single thread for concurrent CLD liveness test #777

8255070: Shenandoah: Use single thread for concurrent CLD liveness test #777

zhengyu123 commented Oct 20, 2020 •

edited by openjdk bot

Loading

bridgekeeper bot commented Oct 20, 2020

openjdk bot commented Oct 20, 2020

mlbridge bot commented Oct 20, 2020 •

edited

Loading

AzeemJiva Oct 21, 2020

zhengyu123 Oct 21, 2020

rkennke Oct 21, 2020

rkennke Oct 21, 2020

zhengyu123 Oct 21, 2020

rkennke left a comment

rkennke Oct 21, 2020

rkennke left a comment

openjdk bot commented Oct 21, 2020 •

edited

Loading

zhengyu123 commented Oct 21, 2020

openjdk bot commented Oct 21, 2020

8255070: Shenandoah: Use single thread for concurrent CLD liveness test #777

8255070: Shenandoah: Use single thread for concurrent CLD liveness test #777

Conversation

zhengyu123 commented Oct 20, 2020 • edited by openjdk bot Loading

Progress

Testing

Issue

Reviewers

Download

bridgekeeper bot commented Oct 20, 2020

openjdk bot commented Oct 20, 2020

mlbridge bot commented Oct 20, 2020 • edited Loading

Webrevs

AzeemJiva Oct 21, 2020

Choose a reason for hiding this comment

zhengyu123 Oct 21, 2020

Choose a reason for hiding this comment

rkennke Oct 21, 2020

Choose a reason for hiding this comment

rkennke Oct 21, 2020

Choose a reason for hiding this comment

zhengyu123 Oct 21, 2020

Choose a reason for hiding this comment

rkennke left a comment

Choose a reason for hiding this comment

rkennke Oct 21, 2020

Choose a reason for hiding this comment

rkennke left a comment

Choose a reason for hiding this comment

openjdk bot commented Oct 21, 2020 • edited Loading

zhengyu123 commented Oct 21, 2020

openjdk bot commented Oct 21, 2020

zhengyu123 commented Oct 20, 2020 •

edited by openjdk bot

Loading

mlbridge bot commented Oct 20, 2020 •

edited

Loading

openjdk bot commented Oct 21, 2020 •

edited

Loading