ThreadReference (Java Debug Interface )
Keywords: com.sun.jdi.ThreadReference interface
Date: 2026-07-22

com.sun.jdi

## Interface ThreadReference

- All Superinterfaces:
    Mirror, ObjectReference, Value

      @Exported
      public interface ThreadReference
      extends ObjectReference

  A thread object from the target VM. A ThreadReference is an `ObjectReference` with additional access to thread-specific information from the target VM.
  Since:
    1.3

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `THREAD_STATUS_MONITOR` Thread is waiting on a java monitor
    `static int` | `THREAD_STATUS_NOT_STARTED` Thread has not yet been started
    `static int` | `THREAD_STATUS_RUNNING` Thread is runnable
    `static int` | `THREAD_STATUS_SLEEPING` Thread is sleeping - Thread.sleep() or JVM_Sleep() was called
    `static int` | `THREAD_STATUS_UNKNOWN` Thread status is unknown
    `static int` | `THREAD_STATUS_WAIT` Thread is waiting - Object.wait() or JVM_MonitorWait() was called
    `static int` | `THREAD_STATUS_ZOMBIE` Thread has completed execution

    - ### Fields inherited from interface com.sun.jdi.ObjectReference

      `INVOKE_NONVIRTUAL, INVOKE_SINGLE_THREADED`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method and Description
    --- | ---
    `ObjectReference` | `currentContendedMonitor()` Returns an `ObjectReference` for the monitor, if any, for which this thread is currently waiting.
    `void` | `forceEarlyReturn(Value value)` Force a method to return before it reaches a return statement.
    `StackFrame` | `frame(int index)` Returns the `StackFrame` at the given index in the thread's current call stack.
    `int` | `frameCount()` Returns the number of stack frames in the thread's current call stack.
    `List<StackFrame>` | `frames()` Returns a List containing each `StackFrame` in the thread's current call stack.
    `List<StackFrame>` | `frames(int start, int length)` Returns a List containing a range of `StackFrame` mirrors from the thread's current call stack.
    `void` | `interrupt()` Interrupts this thread unless the thread has been suspended by the debugger.
    `boolean` | `isAtBreakpoint()` Determines whether the thread is suspended at a breakpoint.
    `boolean` | `isSuspended()` Determines whether the thread has been suspended by the the debugger.
    `String` | `name()` Returns the name of this thread.
    `List<ObjectReference>` | `ownedMonitors()` Returns a List containing an `ObjectReference` for each monitor owned by the thread.
    `List<MonitorInfo>` | `ownedMonitorsAndFrames()` Returns a List containing a `MonitorInfo` object for each monitor owned by the thread.
    `void` | `popFrames(StackFrame frame)` Pop stack frames.
    `void` | `resume()` Resumes this thread.
    `int` | `status()` Returns the thread's status.
    `void` | `stop(ObjectReference throwable)` Stops this thread with an asynchronous exception.
    `void` | `suspend()` Suspends this thread.
    `int` | `suspendCount()` Returns the number of pending suspends for this thread.
    `ThreadGroupReference` | `threadGroup()` Returns this thread's thread group.

    - ### Methods inherited from interface com.sun.jdi.ObjectReference

      `disableCollection, enableCollection, entryCount, equals, getValue, getValues, hashCode, invokeMethod, isCollected, owningThread, referenceType, referringObjects, setValue, uniqueID, waitingThreads`

    - ### Methods inherited from interface com.sun.jdi.Value

      `type`

    - ### Methods inherited from interface com.sun.jdi.Mirror

      `toString, virtualMachine`

- - ### Field Detail

    - #### THREAD_STATUS_UNKNOWN

          static final int THREAD_STATUS_UNKNOWN

      Thread status is unknown
      See Also:
        Constant Field Values

    - #### THREAD_STATUS_ZOMBIE

          static final int THREAD_STATUS_ZOMBIE

      Thread has completed execution
      See Also:
        Constant Field Values

    - #### THREAD_STATUS_RUNNING

          static final int THREAD_STATUS_RUNNING

      Thread is runnable
      See Also:
        Constant Field Values

    - #### THREAD_STATUS_SLEEPING

          static final int THREAD_STATUS_SLEEPING

      Thread is sleeping - Thread.sleep() or JVM_Sleep() was called
      See Also:
        Constant Field Values

    - #### THREAD_STATUS_MONITOR

          static final int THREAD_STATUS_MONITOR

      Thread is waiting on a java monitor
      See Also:
        Constant Field Values

    - #### THREAD_STATUS_WAIT

          static final int THREAD_STATUS_WAIT

      Thread is waiting - Object.wait() or JVM_MonitorWait() was called
      See Also:
        Constant Field Values

    - #### THREAD_STATUS_NOT_STARTED

          static final int THREAD_STATUS_NOT_STARTED

      Thread has not yet been started
      See Also:
        Constant Field Values

  - ### Method Detail

    - #### name

          String name()

      Returns the name of this thread.
      Returns:
        the string containing the thread name.

    - #### suspend

          void suspend()

      Suspends this thread. The thread can be resumed through `resume()` or resumed with other threads through `VirtualMachine.resume()`.

      Unlike `Thread.suspend()`, suspends of both the virtual machine and individual threads are counted. Before a thread will run again, it must be resumed (through `resume()` or `resume()`) the same number of times it has been suspended.

      Suspending single threads with this method has the same dangers as `Thread.suspend()`. If the suspended thread holds a monitor needed by another running thread, deadlock is possible in the target VM (at least until the suspended thread is resumed again).

      The suspended thread is guaranteed to remain suspended until resumed through one of the JDI resume methods mentioned above; the application in the target VM cannot resume the suspended thread through `Thread.resume()`.

      Throws:
        `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.

    - #### resume

          void resume()

      Resumes this thread. If this thread was not previously suspended through `suspend()` or through `VirtualMachine.suspend()`, or because of a SUSPEND_ALL or SUSPEND_EVENT_THREAD event, then invoking this method has no effect. Otherwise, the count of pending suspends on this thread is decremented. If it is decremented to 0, the thread will continue to execute. Note: the normal way to resume from an event related suspension is via `EventSet.resume()`.
      Throws:
        `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.

    - #### suspendCount

          int suspendCount()

      Returns the number of pending suspends for this thread. See `suspend()` for an explanation of counted suspends.
      Returns:
        pending suspend count as an integer

    - #### stop

          void stop(ObjectReference throwable)
             throws InvalidTypeException

      Stops this thread with an asynchronous exception. A debugger thread in the target VM will stop this thread with the given `Throwable` object.
      Parameters:
        `throwable` - the asynchronous exception to throw.
      Throws:
        `InvalidTypeException` - if `throwable` is not an instance of java.lang.Throwable in the target VM.
        `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.
      See Also:
        `Thread.stop(Throwable)`

    - #### interrupt

          void interrupt()

      Interrupts this thread unless the thread has been suspended by the debugger.
      Throws:
        `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.
      See Also:
        `Thread.interrupt()`

    - #### status

          int status()

      Returns the thread's status. If the thread is not suspended the thread's current status is returned. If the thread is suspended, the thread's status before the suspension is returned (or `THREAD_STATUS_UNKNOWN` if this information is not available. `isSuspended()` can be used to determine if the thread has been suspended.
      Returns:
        one of `THREAD_STATUS_UNKNOWN`, `THREAD_STATUS_ZOMBIE`, `THREAD_STATUS_RUNNING`, `THREAD_STATUS_SLEEPING`, `THREAD_STATUS_MONITOR`, `THREAD_STATUS_WAIT`, `THREAD_STATUS_NOT_STARTED`,

    - #### isSuspended

          boolean isSuspended()

      Determines whether the thread has been suspended by the the debugger.
      Returns:
        `true` if the thread is currently suspended; `false` otherwise.

    - #### isAtBreakpoint

          boolean isAtBreakpoint()

      Determines whether the thread is suspended at a breakpoint.
      Returns:
        `true` if the thread is currently stopped at a breakpoint; `false` otherwise.

    - #### threadGroup

          ThreadGroupReference threadGroup()

      Returns this thread's thread group.
      Returns:
        a `ThreadGroupReference` that mirrors this thread's thread group in the target VM.

    - #### frameCount

          int frameCount()
                  throws IncompatibleThreadStateException

      Returns the number of stack frames in the thread's current call stack. The thread must be suspended (normally through an interruption to the VM) to get this information, and it is only valid until the thread is resumed again.
      Returns:
        an integer frame count
      Throws:
        `IncompatibleThreadStateException` - if the thread is not suspended in the target VM

    - #### frames

          List<StackFrame> frames()
                           throws IncompatibleThreadStateException

      Returns a List containing each `StackFrame` in the thread's current call stack. The thread must be suspended (normally through an interruption to the VM) to get this information, and it is only valid until the thread is resumed again.
      Returns:
        a List of `StackFrame` with the current frame first followed by each caller's frame.
      Throws:
        `IncompatibleThreadStateException` - if the thread is not suspended in the target VM

    - #### frame

          StackFrame frame(int index)
                    throws IncompatibleThreadStateException

      Returns the `StackFrame` at the given index in the thread's current call stack. Index 0 retrieves the current frame; higher indices retrieve caller frames. The thread must be suspended (normally through an interruption to the VM) to get this information, and it is only valid until the thread is resumed again.
      Parameters:
        `index` - the desired frame
      Returns:
        the requested `StackFrame`
      Throws:
        `IncompatibleThreadStateException` - if the thread is not suspended in the target VM
        `IndexOutOfBoundsException` - if the index is greater than or equal to `frameCount()` or is negative.

    - #### frames

          List<StackFrame> frames(int start,
                                  int length)
                           throws IncompatibleThreadStateException

      Returns a List containing a range of `StackFrame` mirrors from the thread's current call stack. The thread must be suspended (normally through an interruption to the VM) to get this information, and it is only valid until the thread is resumed again.
      Parameters:
        `start` - the index of the first frame to retrieve. Index 0 represents the current frame.
        `length` - the number of frames to retrieve
      Returns:
        a List of `StackFrame` with the current frame first followed by each caller's frame.
      Throws:
        `IncompatibleThreadStateException` - if the thread is not suspended in the target VM
        `IndexOutOfBoundsException` - if the specified range is not within the range of stack frame indicies. That is, the exception is thrown if any of the following are true:

                start < 0
                start >= frameCount()
                length < 0
                (start+length) > frameCount()

    - #### ownedMonitors

          List<ObjectReference> ownedMonitors()
                                       throws IncompatibleThreadStateException

      Returns a List containing an `ObjectReference` for each monitor owned by the thread. A monitor is owned by a thread if it has been entered (via the synchronized statement or entry into a synchronized method) and has not been relinquished through `Object.wait(long)`.

      Not all target virtual machines support this operation. Use `VirtualMachine.canGetOwnedMonitorInfo()` to determine if the operation is supported.

      Returns:
        a List of `ObjectReference` objects. The list has zero length if no monitors are owned by this thread.
      Throws:
        `UnsupportedOperationException` - if the target virtual machine does not support this operation.
        `IncompatibleThreadStateException` - if the thread is not suspended in the target VM

    - #### ownedMonitorsAndFrames

          List<MonitorInfo> ownedMonitorsAndFrames()
                                            throws IncompatibleThreadStateException

      Returns a List containing a `MonitorInfo` object for each monitor owned by the thread. A monitor is owned by a thread if it has been entered (via the synchronized statement or entry into a synchronized method) and has not been relinquished through `Object.wait(long)`.

      Not all target virtual machines support this operation. Use `VirtualMachine.canGetMonitorFrameInfo()` to determine if the operation is supported.

      Returns:
        a List of `MonitorInfo` objects. The list has zero length if no monitors are owned by this thread.
      Throws:
        `UnsupportedOperationException` - if the target virtual machine does not support this operation.
        `IncompatibleThreadStateException` - if the thread is not suspended in the target VM
      Since:
        1.6

    - #### currentContendedMonitor

          ObjectReference currentContendedMonitor()
                                           throws IncompatibleThreadStateException

      Returns an `ObjectReference` for the monitor, if any, for which this thread is currently waiting. The thread can be waiting for a monitor through entry into a synchronized method, the synchronized statement, or `Object.wait(long)`. The `status()` method can be used to differentiate between the first two cases and the third.

      Not all target virtual machines support this operation. Use `VirtualMachine.canGetCurrentContendedMonitor()` to determine if the operation is supported.

      Returns:
        the `ObjectReference` corresponding to the contended monitor, or null if it is not waiting for a monitor.
      Throws:
        `UnsupportedOperationException` - if the target virtual machine does not support this operation.
        `IncompatibleThreadStateException` - if the thread is not suspended in the target VM

    - #### popFrames

          void popFrames(StackFrame frame)
                  throws IncompatibleThreadStateException

      Pop stack frames.

      All frames up to and including the `frame` are popped off the stack. The frame previous to the parameter `frame` will become the current frame.

      After this operation, this thread will be suspended at the invoke instruction of the target method that created `frame`. The `frame`'s method can be reentered with a step into the instruction.

      The operand stack is restored, however, any changes to the arguments that occurred in the called method, remain. For example, if the method `foo`:

              void foo(int x) {
                  System.out.println("Foo: " + x);
                  x = 4;
                  System.out.println("pop here");
              }

      was called with `foo(7)` and `foo` is popped at the second `println` and resumed, it will print: `Foo: 4`.

      Locks acquired by a popped frame are released when it is popped. This applies to synchronized methods that are popped, and to any synchronized blocks within them.

      Finally blocks are not executed.

      No aspect of state, other than this thread's execution point and locks, is affected by this call. Specifically, the values of fields are unchanged, as are external resources such as I/O streams. Additionally, the target program might be placed in a state that is impossible with normal program flow; for example, order of lock acquisition might be perturbed. Thus the target program may proceed differently than the user would expect.

      The specified thread must be suspended.

      All `StackFrame` objects for this thread are invalidated.

      No events are generated by this method.

      None of the frames through and including the frame for the caller of frame may be native.

      Not all target virtual machines support this operation. Use `VirtualMachine.canPopFrames()` to determine if the operation is supported.

      Parameters:
        `frame` - Stack frame to pop. `frame` is on this thread's call stack.
      Throws:
        `UnsupportedOperationException` - if the target virtual machine does not support this operation - see `VirtualMachine.canPopFrames()`.
        `IncompatibleThreadStateException` - if this thread is not suspended.
        `IllegalArgumentException` - if `frame` is not on this thread's call stack.
        `NativeMethodException` - if one of the frames that would be popped is that of a native method or if the frame previous to frame is native.
        `InvalidStackFrameException` - if `frame` has become invalid. Once this thread is resumed, the stack frame is no longer valid. This exception is also thrown if there are no more frames.
        `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.
      Since:
        1.4

    - #### forceEarlyReturn

          void forceEarlyReturn(Value value)
                         throws InvalidTypeException,
                                ClassNotLoadedException,
                                IncompatibleThreadStateException

      Force a method to return before it reaches a return statement.

      The method which will return early is referred to as the called method. The called method is the current method (as defined by the Frames section in the Java Virtual Machine Specification) for the specified thread at the time this method is called.

      The thread must be suspended. The return occurs when execution of Java programming language code is resumed on this thread. Between the call to this method and resumption of thread execution, the state of the stack is undefined.

      No further instructions are executed in the called method. Specifically, finally blocks are not executed. Note: this can cause inconsistent states in the application.

      A lock acquired by calling the called method (if it is a synchronized method) and locks acquired by entering synchronized blocks within the called method are released. Note: this does not apply to native locks or java.util.concurrent.locks locks.

      Events, such as MethodExit, are generated as they would be in a normal return.

      The called method must be a non-native Java programming language method. Forcing return on a thread with only one frame on the stack causes the thread to exit when resumed.

      The `value` argument is the value that the method is to return. If the return type of the method is void, then value must be a `VoidValue`. Object values must be assignment compatible with the method return type (This implies that the method return type must be loaded through the enclosing class's class loader). Primitive values must be either assignment compatible with the method return type or must be convertible to the variable type without loss of information. See JLS section 5.2 for more information on assignment compatibility.

      Not all target virtual machines support this operation. Use `VirtualMachine.canForceEarlyReturn()` to determine if the operation is supported.

      Parameters:
        `value` - the value the method is to return.
      Throws:
        `UnsupportedOperationException` - if the target virtual machine does not support this operation - see `canForceEarlyReturn()`
        `IncompatibleThreadStateException` - if this thread is not suspended.
        `NativeMethodException` - if the frame to be returned from is that of a native method.
        `InvalidStackFrameException` - if there are no frames.
        `InvalidTypeException` - if the value's type does not match the method's return type.
        `ClassNotLoadedException` - if the method's return type has not yet been loaded through the appropriate class loader.
        `VMCannotBeModifiedException` - if the VirtualMachine is read-only - see `VirtualMachine.canBeModified()`.
      Since:
        1.6

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