8254566: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader #14720

mlchung · 2023-06-29T23:39:55Z

The spec of ClassLoader::getClassLoadingLock is unclear that this method is intended for parallel-capable class loader implementations to provide an alternate implementation. For non-parallel-capable class loaders, this method should return this ClassLoader object. The javadoc uses "the default implementation" which could be interpreted that non-parallel-capable class loaders can also override this implementation, which is not the intent. See https://openjdk.org/groups/core-libs/ClassLoaderProposal.html.

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Issues

JDK-8254566: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader (Bug - P4)
JDK-8311128: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader (CSR)

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David Holmes (@dholmes-ora - Reviewer) ⚠️ Review applies to e9607f4a
Joe Darcy (@jddarcy - Reviewer)

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…quired by non-parallel capable loader

bridgekeeper · 2023-06-29T23:41:21Z

👋 Welcome back mchung! 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 · 2023-06-29T23:43:26Z

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

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mlbridge · 2023-06-29T23:48:59Z

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dholmes-ora

Looks good. One change requested on terminology.

Thanks

dholmes-ora · 2023-06-30T00:04:21Z

src/java.base/share/classes/java/lang/ClassLoader.java

+     *
+     * @apiNote
+     * This method allows parallel capable class loaders to implement
+     * finer-grained locking scheme such that multiple threads may load classes


s/scheme/schemes/

dholmes-ora · 2023-06-30T00:06:08Z

src/java.base/share/classes/java/lang/ClassLoader.java

+     * This method allows parallel capable class loaders to implement
+     * finer-grained locking scheme such that multiple threads may load classes
+     * concurrently without deadlocks.  For non-parallel-capable class loaders,
+     * the {@code ClassLoader} object is held during the class loading operations.


s/is held/is synchronized on/ - as that is the terminology loadClass uses.

Updated per your suggestion.

dholmes-ora

Looks good to me.

openjdk · 2023-06-30T19:12:32Z

@mlchung 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:

8254566: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader

Reviewed-by: dholmes, darcy

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 11 new commits pushed to the master branch:

456bf11: 8310173: Update --release 21 symbol information for JDK 21 build 29
19601eb: 8310993: Missing @SInCE tags in jdk.attach
e8ff74c: 8310987: Missing @SInCE tag(s) in java/util/logging/ErrorManager.java
e3a7e02: 8311162: Simplify and modernize equals and hashCode for java.net
430d6b6: 8309976: Add microbenchmark for stressing code cache
33011ea: 8310946: G1: Refactor G1Policy::next_gc_should_be_mixed
a7d168b: 8311026: Some G1 specific tests do not set -XX:+UseG1GC
c08c983: 8311000: missing @SInCE info in jdk.management
660cd25: 8310988: Missing @SInCE tags in java.management.rmi
2a9e2f6: 8311046: ProblemList gc/z/TestHighUsage.java with Generational ZGC
... and 1 more: https://git.openjdk.org/jdk/compare/11fd34e196b29d2f2fd276c36f59a3c3b3ce7280...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.

mlchung · 2023-07-03T16:03:31Z

/integrate

openjdk · 2023-07-03T16:04:38Z

Going to push as commit b9198f9.
Since your change was applied there have been 29 commits pushed to the master branch:

f393975: 8310743: assert(reserved_rgn != nullptr) failed: Add committed region, No reserved region found
ba974d5: 8310661: JFR: Replace JVM.getJVM() with JVM
496f94b: 8311086: Remove jtreg/gc/startup_warnings
9d2e0b2: 8307934: JRobot.moveMouseTo must access component on EDT
87c79c0: 8309302: java/net/Socket/Timeouts.java fails with AssertionError on test temporal post condition
8e0ca8e: 8310331: JitTester: Exclude java.lang.Math.random
055b4b4: 8310948: Fix ignored-qualifiers warning in Hotspot
2c29705: 8309660: C2: failed: XMM register should be 0-15 (UseKNLSetting and ConvF2HF)
52ee570: 8309209: C2 failed "assert(_stack_guard_state == stack_guard_reserved_disabled) failed: inconsistent state"
faf1b82: 8310656: RISC-V: __builtin___clear_cache can fail silently.
... and 19 more: https://git.openjdk.org/jdk/compare/11fd34e196b29d2f2fd276c36f59a3c3b3ce7280...master

Your commit was automatically rebased without conflicts.

openjdk · 2023-07-03T16:04:53Z

@mlchung Pushed as commit b9198f9.

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

AlanBateman · 2023-07-10T05:20:07Z

src/java.base/share/classes/java/lang/ClassLoader.java

+     * finer-grained locking schemes such that multiple threads may load classes
+     * concurrently without deadlocks.  For non-parallel-capable class loaders,
+     * the {@code ClassLoader} object is synchronized on during the class loading
+     * operations.  Class loaders with non-hierarchical delegation should be


At some point we might want to re-visit the use of "non-hierarchical" (and "hierarchical" in the class description) as deadlocks are also possible with hierarchical delegation when mixing parent-first and child-first delegation. It could be that the the API note provides a strong recommendation the class loader be parallel capable when it is anything other than single parent with parent delegation.

8254566: Clarify the spec of ClassLoader::loadClass about the lock ac…

e87f4b4

…quired by non-parallel capable loader

openjdk bot added the csr Pull request needs approved CSR before integration label Jun 29, 2023

openjdk bot added core-libs core-libs-dev@openjdk.org rfr Pull request is ready for review labels Jun 29, 2023

dholmes-ora suggested changes Jun 30, 2023

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dholmes-ora approved these changes Jun 30, 2023

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make it implSpec per CSR review feedback

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openjdk bot added ready Pull request is ready to be integrated and removed csr Pull request needs approved CSR before integration labels Jun 30, 2023

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AlanBateman reviewed Jul 10, 2023

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mlchung deleted the JDK-8254566 branch August 2, 2023 20:50

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8254566: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader #14720

8254566: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader #14720

mlchung commented Jun 29, 2023 •

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AlanBateman Jul 10, 2023

8254566: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader #14720

8254566: Clarify the spec of ClassLoader::getClassLoadingLock for non-parallel capable loader #14720

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mlchung commented Jun 29, 2023 • edited by openjdk bot Loading

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