RFR: 8356870: HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file updates

[Chen Liang]

On Sat, 24 May 2025 09:33:13 GMT, Shaojin Wen <swen 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
>
> src/java.base/share/classes/jdk/internal/vm/ThreadSnapshot.java line 182:
> 
>> 180:      */
>> 181:     private class ThreadLock {
>> 182:         private static final OwnedLockType[] lockTypeValues = OwnedLockType.values(); // cache
> 
> Suggestion:
> 
>         @Stable
>         private static final OwnedLockType[] lockTypeValues = OwnedLockType.values();

This class can be made final too.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25429#discussion_r2106088224