RFR: 8329109: Threads::print_on() tries to print CPU time for terminated GC threads [v2]

[Matthias Baesken]

On Tue, 2 Apr 2024 12:28:10 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

>> *EDIT 2024-04-02:* Use `Threads::non_java_threads_do(ThreadClosure* tc)` to print non-java threads (commit b2dabc95d760496d4896b30ef1a44cc5c250189d). It uses thread list iterators that synchronize with thread creation and termination. If a non-java thread is about to terminate, it waits for in progress iterations (see [NonJavaThread::remove_from_the_list](https://github.com/openjdk/jdk/blob/47f33a59eaaffc74881fcc9e29d13ff9b2538c2a/src/hotspot/share/runtime/nonJavaThread.cpp#L97-L102)).
>> 
>> Testing:
>> 
>> The output of a minimal example with G1 is almost identical (attached below). The order of non-java threads can differ.
>> 
>> More tests (besides GHA) are pending.
>
> Richard Reingruber has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Equivalent but simpler fix
>  - Revert
>    
>    This reverts commit 568a2bcc7a1c99ba9f95a33dbcb80eb511ead94b.

Looks like a good and simple fix, thanks !  The doc of NonJavaThread::Iterator says 'only live fully-initialized threads can be found in the list' and this is what we need here.

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Marked as reviewed by mbaesken (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18518#pullrequestreview-1976066948