RFR: 8338890: Add monitoring/management interface for the virtual thread scheduler

[ExE Boss]

On Mon, 2 Sep 2024 12:25:05 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> This PR proposes to add a JDK-specific monitoring and management interface for the virtual thread scheduler. The interface is named VirtualThreadSchedulerMXBean and allows JMX based tooling monitor/manage the scheduler's target parallelism and monitor thread counts.
> 
> The JDK 5/6 era JDK-specific management interfaces are in jdk.management/com.sun.management. The proposal here is to start afresh in the jdk.management package, thus establishing a "new home" for JDK-specific management interfaces going forward.
> 
> jdk.test.lib.thread.VThreadRunner is test infrastructure used by several tests to set or ensure some level of parallelism. This is changed from using deep reflection to using the MXBean to access the target parallelism, which requires changes to the `@modules` tag tests in a number of tests (some tests no longer need to open java.base/java.lang).
> 
> (The changes proposed here have been in the loom repo for some time. A related command for the jcmd tool is also in that repo and will be proposed separately).

Typo (`imp` → `impl`):

The `BaseVirtualThreadSchedulerImpl` hierarchy can be `sealed`:

src/jdk.management/share/classes/com/sun/management/internal/VirtualThreadSchedulerImpls.java line 56:

> 54:      * Base implementation of VirtualThreadSchedulerMXBean.
> 55:      */
> 56:     private abstract static class BaseVirtualThreadSchedulerImpl

Suggestion:

    private abstract static sealed class BaseVirtualThreadSchedulerImpl

src/jdk.management/share/classes/com/sun/management/internal/VirtualThreadSchedulerImpls.java line 59:

> 57:             implements VirtualThreadSchedulerMXBean {
> 58: 
> 59:         abstract void impSetParallelism(int size);

Suggestion:

        abstract void implSetParallelism(int size);

src/jdk.management/share/classes/com/sun/management/internal/VirtualThreadSchedulerImpls.java line 64:

> 62:         public final void setParallelism(int size) {
> 63:             Util.checkControlAccess();
> 64:             impSetParallelism(size);

Suggestion:

            implSetParallelism(size);

src/jdk.management/share/classes/com/sun/management/internal/VirtualThreadSchedulerImpls.java line 97:

> 95:      * implemented with continuations + scheduler.
> 96:      */
> 97:     private static class VirtualThreadSchedulerImpl extends BaseVirtualThreadSchedulerImpl {

Suggestion:

    private static final class VirtualThreadSchedulerImpl extends BaseVirtualThreadSchedulerImpl {

src/jdk.management/share/classes/com/sun/management/internal/VirtualThreadSchedulerImpls.java line 119:

> 117: 
> 118:         @Override
> 119:         void impSetParallelism(int size) {

Suggestion:

        void implSetParallelism(int size) {

src/jdk.management/share/classes/com/sun/management/internal/VirtualThreadSchedulerImpls.java line 159:

> 157:      * by platform threads.
> 158:      */
> 159:     private static class BoundVirtualThreadSchedulerImpl extends BaseVirtualThreadSchedulerImpl {

Suggestion:

    private static final class BoundVirtualThreadSchedulerImpl extends BaseVirtualThreadSchedulerImpl {

src/jdk.management/share/classes/com/sun/management/internal/VirtualThreadSchedulerImpls.java line 167:

> 165: 
> 166:         @Override
> 167:         void impSetParallelism(int size) {

Suggestion:

        void implSetParallelism(int size) {

-------------

PR Review: https://git.openjdk.org/jdk/pull/20816#pullrequestreview-2276238096
PR Review: https://git.openjdk.org/jdk/pull/20816#pullrequestreview-2276600238
PR Review Comment: https://git.openjdk.org/jdk/pull/20816#discussion_r1741551781
PR Review Comment: https://git.openjdk.org/jdk/pull/20816#discussion_r1741310375
PR Review Comment: https://git.openjdk.org/jdk/pull/20816#discussion_r1741310424
PR Review Comment: https://git.openjdk.org/jdk/pull/20816#discussion_r1741552166
PR Review Comment: https://git.openjdk.org/jdk/pull/20816#discussion_r1741310517
PR Review Comment: https://git.openjdk.org/jdk/pull/20816#discussion_r1741552822
PR Review Comment: https://git.openjdk.org/jdk/pull/20816#discussion_r1741310573