RFR: 8321270: Virtual Thread.yield consumes parking permit

[Serguei Spitsyn]

On Mon, 4 Dec 2023 16:08:32 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> When a virtual thread continues after Thread.yield it currently consumes thread's parking permit. This is an oversight, the parking permit should only be consumed when continuing after park.
> 
> The changes are straight-forward. The internal "RUNNABLE" state is replaced with UNPARKED and YIELDED state, effectively encoding the previous state. So for the most part, it's just replacing the usages of RUNNABLE. The additional states require refactoring tryGetStackTrace, this is the method that is used for Thread::getStackTrace when the virtual thread is unmounted. It is also changed to not not swallow the REE if the reesubmit fails (tryStackTrace has to resubmit as the task for the thread may run, or the thread unparked, while "suspended" and sampling its stack trace). The changes are a subset of larger changes in the loom repo, future PRs will propose to bring in other changes to get main line up to date.
> 
> For testing the existing ThreadAPI has new test cases.
> 
> Testing: test1-5. This includes the JVMTI tests as it maps the thread states to JVMTI thread states.

src/java.base/share/classes/java/lang/VirtualThread.java line 116:

> 114:     private static final int NEW      = 0;
> 115:     private static final int STARTED  = 1;
> 116:     private static final int RUNNING  = 2;     // runnable-unmounted

Just want to make sure this change is intentional.
Before the comment was:  `// runnable-mounted`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16953#discussion_r1414528008