java.lang
class ThreadGroup

java.lang.Object java.lang.ThreadGroup

All Implemented Interfaces:

Thread.UncaughtExceptionHandler

Most common ways to construct:

Vector groups = …;
int i = …;

ThreadGroup tg = (ThreadGroup)groups.elementAt(i);

Based on 9 examples

 

ThreadGroup somegroup = new ThreadGroup("GroupA");

Based on 8 examples

public class ThreadGroup
extends Object
implements Thread.UncaughtExceptionHandler

A thread group represents a set of threads. In addition, a thread group can also include other thread groups. The thread groups form a tree in which every thread group except the initial thread group has a parent.

A thread is allowed to access information about its own thread group, but not to access information about its thread group's parent thread group or any other thread groups.

ThreadGroup

public ThreadGroup(String name)

Constructs a new thread group. The parent of this new group is the thread group of the currently running thread.

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

Parameters:

name - the name of the new thread group.

ThreadGroup

public ThreadGroup(ThreadGroup parent,
                   String name)

Creates a new thread group. The parent of this new group is the specified thread group.

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

Parameters:

parent - the parent thread group.

name - the name of the new thread group.

activeCount

public int activeCount()

Returns an estimate of the number of active threads in this thread group. The result might not reflect concurrent activity, and might be affected by the presence of certain system threads.

Due to the inherently imprecise nature of the result, it is recommended that this method only be used for informational purposes.

Returns:

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

activeGroupCount

public int activeGroupCount()

Returns an estimate of the number of active groups in this thread group. The result might not reflect concurrent activity.

Due to the inherently imprecise nature of the result, it is recommended that this method only be used for informational purposes.

Returns:

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

allowThreadSuspension

public boolean allowThreadSuspension(boolean b)

Used by VM to control lowmem implicit suspension.

Parameters:

b - boolean to allow or disallow suspension

Returns:

true on success

checkAccess

public final void checkAccess()

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.

destroy

public final void destroy()

Destroys this thread group and all of its subgroups. This thread group must be empty, indicating that all threads that had been in this thread group have since stopped.

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

enumerate

public int enumerate(ThreadGroup[] list)

Copies into the specified array references to every active subgroup in this thread group.

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

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 active 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 informational purposes.

Parameters:

list - an array into which to place the list of thread groups.

Returns:

the number of thread groups put into the array.

enumerate

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

Copies into the specified array references to every active subgroup in this thread group. If the recurse flag is true, references to all active subgroups of the subgroups and so forth are also included.

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

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 active 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 informational purposes.

Parameters:

list - an array into which to place the list of threads.

recurse - a flag indicating whether to recursively enumerate all included thread groups.

Returns:

the number of thread groups put into the array.

enumerate

public int enumerate(Thread[] list)

Copies into the specified array every active thread in this thread group and its subgroups.

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

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 active thread in this thread group and its subgroups, 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 informational purposes.

Parameters:

list - an array into which to place the list of threads.

Returns:

the number of threads put into the array.

enumerate

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

Copies into the specified array every active thread in this thread group. If the recurse flag is true, references to every active thread in this thread's subgroups are also included. If the array is too short to hold all the threads, the extra threads are silently ignored.

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

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 active 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 informational purposes.

Parameters:

list - an array into which to place the list of threads.

recurse - a flag indicating whether also to include threads in thread groups that are subgroups of this thread group.

Returns:

the number of threads placed into the array.

getMaxPriority

public final int getMaxPriority()

Returns the maximum priority of this thread group. Threads that are part of this group cannot have a higher priority than the maximum priority.

Returns:

the maximum priority that a thread in this thread group can have.

getName

public final String getName()

Returns the name of this thread group.

Returns:

the name of this thread group.

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.

interrupt

public final void interrupt()

Interrupts all threads in this thread group.

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

This method then calls the interrupt method on all the threads in this thread group and in all of its subgroups.

isDaemon

public final boolean isDaemon()

Tests if this thread group is a daemon thread group. A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

Returns:

true if this thread group is a daemon thread group; false otherwise.

isDestroyed

public synchronized boolean isDestroyed()

Tests if this thread group has been destroyed.

Returns:

true if this object is destroyed

list

public void list()

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

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.

Returns:

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

resume

public final void resume()

Resumes all threads in this thread group.

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

This method then calls the resume method on all the threads in this thread group and in all of its sub groups.

setDaemon

public final void setDaemon(boolean daemon)

Changes the daemon status of this thread group.

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

A daemon thread group is automatically destroyed when its last thread is stopped or its last thread group is destroyed.

Parameters:

daemon - if true, marks this thread group as a daemon thread group; otherwise, marks this thread group as normal.

setMaxPriority

public final void setMaxPriority(int pri)

Sets the maximum priority of the group. Threads in the thread group that already have a higher priority are not affected.

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 {@link Thread#MIN_PRIORITY} or greater than {@link 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.

stop

public final void stop()

Stops all threads in this thread group.

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

This method then calls the stop method on all the threads in this thread group and in all of its subgroups.

suspend

public final void suspend()

Suspends all threads in this thread group.

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

This method then calls the suspend method on all the threads in this thread group and in all of its subgroups.

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.

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 {@link 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 {@linkplain Thread#getDefaultUncaughtExceptionHandler default uncaught exception handler} installed, and if so, its uncaughtException method is called with the same two arguments.
• Otherwise, this method determines if the Throwable argument is an instance of {@link ThreadDeath}. If so, nothing special is done. Otherwise, a message containing the thread's name, as returned from the thread's {@link Thread#getName getName} method, and a stack backtrace, using the Throwable's {@link Throwable#printStackTrace printStackTrace} method, is printed to the {@linkplain System#err standard error stream}.

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

Parameters:

t - the thread that is about to exit.

e - the uncaught exception.