ThreadGroupReference (Java SE 26 & JDK 26)
Description: declaration: module: jdk.jdi, package: com.sun.jdi, interface: ThreadGroupReference
Keywords: com.sun.jdi.ThreadGroupReference interface

# Interface ThreadGroupReference

All Superinterfaces:
  `Mirror, ObjectReference, Value`

public interface ThreadGroupReference extends ObjectReference
A thread group object from the target VM. A ThreadGroupReference is an `ObjectReference` with additional access to threadgroup-specific information from the target VM.

Since:
  1.3

- ## Field Summary

  ### Fields declared in interface ObjectReference

  `INVOKE_NONVIRTUAL, INVOKE_SINGLE_THREADED`
  Modifier and Type
  Field
  Description
  `static final int`
  `INVOKE_NONVIRTUAL`
  Perform non-virtual method invocation
  `static final int`
  `INVOKE_SINGLE_THREADED`
  Perform method invocation with only the invoking thread resumed

- ## Method Summary

  Modifier and Type
  Method
  Description
  `String`
  `name()`
  Returns the name of this thread group.
  `ThreadGroupReference`
  `parent()`
  Returns the parent of this thread group.
  `void`
  `resume()`
  Resumes all threads in this thread group.
  `void`
  `suspend()`
  Suspends all threads in this thread group.
  `List<ThreadGroupReference>`
  `threadGroups()`
  Returns a List containing a `ThreadGroupReference` for each subgroup.
  `List<ThreadReference>`
  `threads()`
  Returns a List containing a `ThreadReference` for each live platform thread in this thread group.

  ### Methods declared in interface Mirror

  `toString, virtualMachine`
  Modifier and Type
  Method
  Description
  `String`
  `toString()`
  Returns a String describing this mirror
  `VirtualMachine`
  `virtualMachine()`
  Gets the VirtualMachine to which this Mirror belongs.

  ### Methods declared in interface ObjectReference

  `disableCollection, enableCollection, entryCount, equals, getValue, getValues, hashCode, invokeMethod, isCollected, owningThread, referenceType, referringObjects, setValue, uniqueID, waitingThreads`
  Modifier and Type
  Method
  Description
  `void`
  `disableCollection()`
  Prevents garbage collection for this object.
  `void`
  `enableCollection()`
  Permits garbage collection for this object.
  `int`
  `entryCount()`
  Returns the number of times this object's monitor has been entered by the current owning thread if the owning thread is platform thread; Returns 0 if not owned by a platform thread.
  `boolean`
  `equals(Object obj)`
  Compares the specified Object with this ObjectReference for equality.
  `Value`
  `getValue(Field sig)`
  Gets the value of a given instance or static field in this object.
  `Map<Field,Value>`
  `getValues(List<? extends Field> fields)`
  Gets the value of multiple instance and/or static fields in this object.
  `int`
  `hashCode()`
  Returns the hash code value for this ObjectReference.
  `Value`
  `invokeMethod(ThreadReference thread, Method method, List<? extends Value> arguments, int options)`
  Invokes the specified `Method` on this object in the target VM.
  `boolean`
  `isCollected()`
  Determines if this object has been garbage collected in the target VM.
  `ThreadReference`
  `owningThread()`
  Returns a `ThreadReference` for the platform thread, if any, which currently owns this object's monitor.
  `ReferenceType`
  `referenceType()`
  Gets the `ReferenceType` that mirrors the type of this object.
  `List<ObjectReference>`
  `referringObjects(long maxReferrers)`
  Returns objects that directly reference this object.
  `void`
  `setValue(Field field, Value value)`
  Sets the value of a given instance or static field in this object.
  `long`
  `uniqueID()`
  Returns a unique identifier for this ObjectReference.
  `List<ThreadReference>`
  `waitingThreads()`
  Returns a List containing a `ThreadReference` for each platform thread currently waiting for this object's monitor.

  ### Methods declared in interface Value

  `type`
  Modifier and Type
  Method
  Description
  `Type`
  `type()`
  Returns the run-time type of this value.

- ## Method Details

  - ### name

    String name()
    Returns the name of this thread group.
    Returns:
      the string containing the thread group name.

  - ### parent

    ThreadGroupReference parent()
    Returns the parent of this thread group.
    Returns:
      a `ThreadGroupReference` mirroring the parent of this thread group in the target VM, or null if this is a top-level thread group.

  - ### suspend

    void suspend()
    Suspends all threads in this thread group. Each thread in this group and in all of its subgroups will be suspended as described in `ThreadReference.suspend()`. This is not guaranteed to be an atomic operation; if the target VM is not interrupted at the time this method is called, it is possible that new threads will be created between the time that threads are enumerated and all of them have been suspended.
    Throws:
      `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.

  - ### resume

    void resume()
    Resumes all threads in this thread group. Each thread in this group and in all of its subgroups will be resumed as described in `ThreadReference.resume()`.
    Throws:
      `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.

  - ### threads

    List<ThreadReference> threads()
    Returns a List containing a `ThreadReference` for each live platform thread in this thread group. Virtual threads are not included. Only the live platform threads in this immediate thread group (and not its subgroups) are returned. A thread is alive if it has been started and has not terminated.
    Returns:
      a List of `ThreadReference` objects mirroring the live platform threads from this thread group in the target VM.

  - ### threadGroups

    List<ThreadGroupReference> threadGroups()
    Returns a List containing a `ThreadGroupReference` for each subgroup. Only the thread groups in this immediate thread group (and not its subgroups) are returned.
    Returns:
      a List of `ThreadGroupReference` objects mirroring the thread groups from this thread group in the target VM.