RFR: 8302899: Executors.newSingleThreadExecutor can use Cleaner to shutdown executor [v4]

[Daniel Fuchs]

On Thu, 23 Feb 2023 08:31:36 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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Merge
>  - Improve SM scenario
>  - Keep reference to Cleanable
>  - Merge
>  - Fix typo in comment, remove blank line
>  - Replace older test
>  - Initial commit

src/java.base/share/classes/java/util/concurrent/Executors.java line 830:

> 828:      * ExecutorService when the wrapper becomes phantom reachable.
> 829:      */
> 830:     private static class AutoShutdownDelegatedExecutorService

nit: if it's not extended anywhere maybe it could be marked final as well.

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