RFR: 8302899: Executors.newSingleThreadExecutor can use Cleaner to shutdown executor [v2]

[Brent Christian]

On Tue, 21 Feb 2023 18:24:05 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Executors.newSingleThreadExecutor returns a delegating ExecutorService that has finalizer to shutdown the underlying TPE when the wrapper is finalizable. It goes back to JDK 6 and JDK-6399443. This is the last non-empty finalizer in java.base. Removing it will likely lead to bug reports/complaints as the current behavior goes back to 2006. So the proposal is to just replace it with a Cleaner, trivially done in this case. As part of the changes, I've replaced the existing test with a more modern test that exercises more scenarios.
>
> Alan Bateman has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo in comment, remove blank line

src/java.base/share/classes/java/util/concurrent/Executors.java line 837:

> 835:         }
> 836:     }
> 837: 

You might consider keeping a dedicated subclass ("CleanableDelegatedExecutorService"?). Such a class could save the Cleanable from Cleaner.register(), and override the shutdown() method to call Cleanable.clean(). This would reduce GC reference tracking, for instance in places where newSingleThreadExecutor() is used in a try-with-resources.

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PR: https://git.openjdk.org/jdk/pull/12675