Class ThreadGroup

Method Details

• getName

  public final String getName()

  Returns the name of this thread group.

  Returns:

  the name of this thread group, may be null

• getParent

  public final ThreadGroup getParent()

  Returns the parent of this thread group.

  First, if the parent is not null, the checkAccess method of the parent thread group is called with no arguments; this may result in a security exception.

  Returns:

  the parent of this thread group. The top-level thread group is the only thread group whose parent is null.

  Throws:

  SecurityException - if the current thread cannot modify this thread group.

  See Also:

  • checkAccess()
  • SecurityException
  • RuntimePermission

• getMaxPriority

  public final int getMaxPriority()

  Returns the maximum priority of this thread group. This is the maximum priority for new threads created in the thread group.

  Returns:

  the maximum priority for new threads created in the thread group

  See Also:

  • setMaxPriority(int)

• isDaemon

  @Deprecated(since="16", forRemoval=true) public final boolean isDaemon()

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method originally indicated if the thread group is a daemon thread group that is automatically destroyed when its last thread terminates. The concept of daemon thread group no longer exists. A thread group is eligible to be GC'ed when there are no live threads in the group and it is otherwise unreachable.

  Returns the daemon status of this thread group. The daemon status is not used for anything.

  Returns:

  the daemon status of this thread group

• isDestroyed

  @Deprecated(since="16", forRemoval=true) public boolean isDestroyed()

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method originally indicated if the thread group is destroyed. The ability to destroy a thread group and the concept of a destroyed thread group no longer exists. A thread group is eligible to be GC'ed when there are no live threads in the group and it is otherwise unreachable.

  Returns false.

  Returns:

  false

  Since:

  1.1

• setDaemon

  @Deprecated(since="16", forRemoval=true) public final void setDaemon(boolean daemon)

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method originally configured whether the thread group is a daemon thread group that is automatically destroyed when its last thread terminates. The concept of daemon thread group no longer exists. A thread group is eligible to be GC'ed when there are no live threads in the group and it is otherwise unreachable.

  Sets the daemon status of this thread group. The daemon status is not used for anything.

  First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

  Parameters:

  daemon - the daemon status

  Throws:

  SecurityException - if the current thread cannot modify this thread group.

  See Also:

  • SecurityException
  • checkAccess()

• setMaxPriority

  public final void setMaxPriority(int pri)

  Sets the maximum priority of the group. The maximum priority of the ThreadGroup for virtual threads is not changed by this method (the new priority is ignored). Threads in the thread group (or subgroups) that already have a higher priority are not affected by this method.

  First, the checkAccess method of this thread group is called with no arguments; this may result in a security exception.

  If the pri argument is less than Thread.MIN_PRIORITY or greater than Thread.MAX_PRIORITY, the maximum priority of the group remains unchanged.

  Otherwise, the priority of this ThreadGroup object is set to the smaller of the specified pri and the maximum permitted priority of the parent of this thread group. (If this thread group is the system thread group, which has no parent, then its maximum priority is simply set to pri.) Then this method is called recursively, with pri as its argument, for every thread group that belongs to this thread group.

  Parameters:

  pri - the new priority of the thread group.

  Throws:

  SecurityException - if the current thread cannot modify this thread group.

  See Also:

  • getMaxPriority()
  • SecurityException
  • checkAccess()

• parentOf

  public final boolean parentOf(ThreadGroup g)

  Tests if this thread group is either the thread group argument or one of its ancestor thread groups.

  Parameters:

  g - a thread group, can be null

  Returns:

  true if this thread group is the thread group argument or one of its ancestor thread groups; false otherwise.

• checkAccess

  @Deprecated(since="17", forRemoval=true) public final void checkAccess()

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method is only useful in conjunction with the Security Manager, which is deprecated and subject to removal in a future release. Consequently, this method is also deprecated and subject to removal. There is no replacement for the Security Manager or this method.

  Determines if the currently running thread has permission to modify this thread group.

  If there is a security manager, its checkAccess method is called with this thread group as its argument. This may result in throwing a SecurityException.

  Throws:

  SecurityException - if the current thread is not allowed to access this thread group.

  See Also:

  • SecurityManager.checkAccess(java.lang.ThreadGroup)

• activeCount

  public int activeCount()

  Returns an estimate of the number of live platform threads in this thread group and its subgroups. Virtual threads are not included in the estimate. This method recursively iterates over all subgroups in this thread group.

  The value returned is only an estimate because the number of threads may change dynamically while this method traverses internal data structures, and might be affected by the presence of certain system threads. This method is intended primarily for debugging and monitoring purposes.

  Returns:

  an estimate of the number of live threads in this thread group and in any other thread group that has this thread group as an ancestor

• enumerate

  public int enumerate(Thread[] list)

  Copies into the specified array every live platform thread in this thread group and its subgroups. Virtual threads are not enumerated by this method.

  An invocation of this method behaves in exactly the same way as the invocation

  enumerate(list, true)

  Parameters:

  list - an array into which to put the list of threads

  Returns:

  the number of threads put into the array

  Throws:

  SecurityException - if checkAccess determines that the current thread cannot access this thread group

• enumerate

  public int enumerate(Thread[] list, boolean recurse)

  Copies into the specified array every live platform thread in this thread group. Virtual threads are not enumerated by this method. If recurse is true, this method recursively enumerates all subgroups of this thread group and references to every live platform thread in these subgroups are also included. If the array is too short to hold all the threads, the extra threads are silently ignored.

  An application might use the activeCount method to get an estimate of how big the array should be, however if the array is too short to hold all the threads, the extra threads are silently ignored. If it is critical to obtain every live thread in this thread group, the caller should verify that the returned int value is strictly less than the length of list.

  Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.

  Parameters:

  list - an array into which to put the list of threads

  recurse - if true, recursively enumerate all subgroups of this thread group

  Returns:

  the number of threads put into the array

  Throws:

  SecurityException - if checkAccess determines that the current thread cannot access this thread group

• activeGroupCount

  public int activeGroupCount()

  Returns an estimate of the number of groups in this thread group and its subgroups. Recursively iterates over all subgroups in this thread group.

  The value returned is only an estimate because the number of thread groups may change dynamically while this method traverses internal data structures. This method is intended primarily for debugging and monitoring purposes.

  Returns:

  the number of thread groups with this thread group as an ancestor

• enumerate

  public int enumerate(ThreadGroup[] list)

  Copies into the specified array references to every subgroup in this thread group and its subgroups.

  An invocation of this method behaves in exactly the same way as the invocation

  enumerate(list, true)

  Parameters:

  list - an array into which to put the list of thread groups

  Returns:

  the number of thread groups put into the array

  Throws:

  SecurityException - if checkAccess determines that the current thread cannot access this thread group

• enumerate

  public int enumerate(ThreadGroup[] list, boolean recurse)

  Copies into the specified array references to every subgroup in this thread group. If recurse is true, this method recursively enumerates all subgroups of this thread group and references to every thread group in these subgroups are also included.

  An application might use the activeGroupCount method to get an estimate of how big the array should be, however if the array is too short to hold all the thread groups, the extra thread groups are silently ignored. If it is critical to obtain every subgroup in this thread group, the caller should verify that the returned int value is strictly less than the length of list.

  Due to the inherent race condition in this method, it is recommended that the method only be used for debugging and monitoring purposes.

  Parameters:

  list - an array into which to put the list of thread groups

  recurse - if true, recursively enumerate all subgroups

  Returns:

  the number of thread groups put into the array

  Throws:

  SecurityException - if checkAccess determines that the current thread cannot access this thread group

• stop

  @Deprecated(since="1.2", forRemoval=true) public final void stop()

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method was originally specified to stop all threads in the thread group. It was inherently unsafe.

  Throws UnsupportedOperationException.

• interrupt

  public final void interrupt()

  Interrupts all live platform threads in this thread group and its subgroups.

  Throws:

  SecurityException - if the current thread is not allowed to access this thread group or any of the threads in the thread group.

  Since:

  1.2

  See Also:

  • Thread.interrupt()
  • SecurityException
  • checkAccess()

• suspend

  @Deprecated(since="1.2", forRemoval=true) public final void suspend()

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method was originally specified to suspend all threads in the thread group.

  Throws UnsupportedOperationException.

• resume

  @Deprecated(since="1.2", forRemoval=true) public final void resume()

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method was originally specified to resume all threads in the thread group.

  Throws UnsupportedOperationException.

• destroy

  @Deprecated(since="16", forRemoval=true) public final void destroy()

  Deprecated, for removal: This API element is subject to removal in a future version.

  This method was originally specified to destroy an empty thread group. The ability to explicitly destroy a thread group no longer exists. A thread group is eligible to be GC'ed when there are no live threads in the group and it is otherwise unreachable.

  Does nothing.

• list

  public void list()

  Prints information about this thread group to the standard output. This method is useful only for debugging.

• uncaughtException

  public void uncaughtException(Thread t, Throwable e)

  Called by the Java Virtual Machine when a thread in this thread group stops because of an uncaught exception, and the thread does not have a specific Thread.UncaughtExceptionHandler installed.

  The uncaughtException method of ThreadGroup does the following:

  • If this thread group has a parent thread group, the uncaughtException method of that parent is called with the same two arguments.
  • Otherwise, this method checks to see if there is a default uncaught exception handler installed, and if so, its uncaughtException method is called with the same two arguments.
  • Otherwise, a message containing the thread's name, as returned from the thread's getName method, and a stack backtrace, using the Throwable's printStackTrace method, is printed to the standard error stream.

  Applications can override this method in subclasses of ThreadGroup to provide alternative handling of uncaught exceptions.

  Specified by:

  uncaughtException in interface Thread.UncaughtExceptionHandler

  Parameters:

  t - the thread that is about to exit.

  e - the uncaught exception.

• toString

  public String toString()

  Returns a string representation of this Thread group.

  Overrides:

  toString in class Object

  Returns:

  a string representation of this thread group.