RFR: 8356870: HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file updates [v3]

[Kevin Walls]

On Thu, 29 May 2025 10:15:20 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Updates the thread dump generated by HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file to include thread state and lock information. Also update the HotSpotDiagnosticMXBean.dumpThreads API description to link to a description of the JSON format dump as that format is intended to be parseable/read by tools.
>> 
>> This PR is dependent on [pull/25425](https://github.com/openjdk/jdk/pull/25425). As noted in that PR, the changes accumulated in the loom repo, and have been split up to make it easier to review.
>> 
>> The changes include some re-implementation of ThreadDumper. This is because it used PrintStream and didn't fail if there was an I/O error, e.g. file system full. Furthermore, the indentation to pretty print the json was fragile and hard to maintain so this is changed to use a supporting writer class to do this.
>> 
>> Test coverage is significantly expanded, including updating the test library that is used by several tests to parse the thread dump.
>> 
>> Testing: tier1-6
>
> 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 five additional commits since the last revision:
> 
>  - Temp fixed until fixed in pull/25425
>  - Sync up from loom repo, includes review comments
>  - Merge branch 'pull/25425' into JDK-8356870
>  - Merge branch 'pull/25425' into JDK-8356870
>  - Initial commit

src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java line 96:

> 94:      * Generate a thread dump in plain text or JSON format to a byte array, UTF-8 encoded.
> 95:      * This method is the implementation of the Thread.dump_to_file diagnostic command
> 96:      * when a file path is not specified. It returns the thread and/or message to send

Comment nit: maybe "...returns the thread dump text and/or message..."?
(also line 120)

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PR Review Comment: https://git.openjdk.org/jdk/pull/25429#discussion_r2116269128