W3cubDocs

Interface VirtualThreadSchedulerMXBean

All Superinterfaces:: PlatformManagedObject

public interface VirtualThreadSchedulerMXBean extends PlatformManagedObject

Management interface for the JDK's virtual thread scheduler.

VirtualThreadSchedulerMXBean supports monitoring of the virtual thread scheduler's target parallelism, the platform threads used by the scheduler, and the number of virtual threads queued to the scheduler. It also supports dynamically changing the scheduler's target parallelism.

The management interface is registered with the platform MBeanServer. The ObjectName that uniquely identifies the management interface within the MBeanServer is: "jdk.management:type=VirtualThreadScheduler".

Direct access to the MXBean interface can be obtained with ManagementFactory.getPlatformMXBean(Class).

Since:: 24

Method Summary

Modifier and Type	Method	Description
`int`	`getMountedVirtualThreadCount()`	Returns an estimate of the number of virtual threads that are currently mounted by the scheduler; `-1` if not known.
`int`	`getParallelism()`	Returns the scheduler's target parallelism.
`int`	`getPoolSize()`	Returns the current number of platform threads that the scheduler has started but have not terminated; `-1` if not known.
`long`	`getQueuedVirtualThreadCount()`	Returns an estimate of the number of virtual threads that are queued to the scheduler to start or continue execution; `-1` if not known.
`void`	`setParallelism(int size)`	Sets the scheduler's target parallelism.

Methods declared in interface PlatformManagedObject

getObjectName

Method Details

getParallelism

int getParallelism()

Returns the scheduler's target parallelism.

Returns:

the scheduler's target parallelism

See Also:

setParallelism

void setParallelism(int size)

Sets the scheduler's target parallelism.

Increasing the target parallelism allows the scheduler to use more platform threads to carry virtual threads if required. Decreasing the target parallelism reduces the number of threads that the scheduler may use to carry virtual threads.

API Note:

If virtual threads are mounting and unmounting frequently then downward adjustment of the target parallelism will likely come into effect quickly.

Implementation Note:

The JDK's virtual thread scheduler is a ForkJoinPool. Target parallelism defaults to the number of available processors. The minimum target parallelism is 1, the maximum target parallelism is 32767.

Parameters:

size - the target parallelism level

Throws:

IllegalArgumentException - if size is less than the minimum, or greater than the maximum, supported by the scheduler

UnsupportedOperationException - if changing the target parallelism is not suppored by the scheduler

See Also:

getPoolSize

int getPoolSize()

Returns the current number of platform threads that the scheduler has started but have not terminated; -1 if not known.

The count includes the platform threads that are currently carrying virtual threads and the platform threads that are not currently carrying virtual threads. The thread count may be greater than the scheduler's target parallelism.

Implementation Note:: The JDK's virtual thread scheduler is a ForkJoinPool. The pool size is the number of worker threads.
Returns:: the current number of platform threads that the scheduler has started but have not terminated; -1 if not known

getMountedVirtualThreadCount

int getMountedVirtualThreadCount()

Returns an estimate of the number of virtual threads that are currently mounted by the scheduler; -1 if not known.

The number of mounted virtual threads is equal to the number of platform threads carrying virtual threads.

Implementation Note:: This method may overestimate the number of virtual threads that are mounted.
Returns:: an estimate of the number of virtual threads that are currently mounted by the scheduler; -1 if not known

getQueuedVirtualThreadCount

long getQueuedVirtualThreadCount()

Returns an estimate of the number of virtual threads that are queued to the scheduler to start or continue execution; -1 if not known.

Implementation Note:: This method may overestimate the number of virtual threads that are queued to execute.
Returns:: an estimate of the number of virtual threads that are queued to the scheduler to start or continue execution; -1 if not known

© 1993, 2025, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/25/docs/api/jdk.management/jdk/management/VirtualThreadSchedulerMXBean.html