RFR: 8309406: Change jdk.trackAllThreads to default to true

[Chris Plummer]

On Sat, 3 Jun 2023 13:41:53 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> Virtual threads created directly with the Thread API are not included in the new thread dump by default. This was a source of confusion in JDK 19/20 when virtual threads were in preview. We have decided to switch the default so that all virtual threads are observable. Future work will reduce/remove the overhead of tracking threads in the root container. The change proposed here has no impact to virtual threads created with the virtual ThreadPerTaskExecutor or StructuredTaskScope.
> 
> With jdk.trackAllThreads defaulting to true then the need for SharedThreadContainer to count threads can go away, as does the need for RootContainer::threads to return virtual threads blocked on I/O.
> 
> Most of the changes are to the test HotSpotDiagnosticMXBean/DumpThreads.java as this is expanded to cover more cases, and specifically more cases with thread groupings that correspond to the ThreadPerTaskExecutor and thread pools.
> 
> Testing: Test1-5

Marked as reviewed by cjplummer (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/14300#pullrequestreview-1463531717