Documentation  › java.lang  › ThreadGroup
 
 


  ThreadGroup
  public

  Inherits From:   Object
  Conforms To:   none
  Declared In:   java.lang


Class Description
 
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.



Class Variables
 
None declared in this class.


Instance Variables
 
None declared in this class.


Constructors
 
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.


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.



Class Methods
 
None declared in this class.


Instance Methods
 
activeCount
public int activeCount( )

Returns an estimate of the number of active threads in this thread group.


activeGroupCount
public int activeGroupCount( )

Returns an estimate of the number of active groups in this thread group.


allowThreadSuspension
public boolean allowThreadSuspension( boolean b )

Used by VM to control lowmem implicit suspension.


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( 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 should use the activeCount method to get an estimate of how big the array should be. If the array is too short to hold all the threads, the extra threads are silently ignored.


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 should use the activeCount method to get an estimate of how big the array should be.


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 should use the activeGroupCount method to get an estimate of how big the array should be. If the array is too short to hold all the thread groups, the extra thread groups are silently ignored.


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 should use the activeGroupCount method to get an estimate of how big the array should be.


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.


getName
public final String getName( )

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.


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.


isDestroyed
public synchronized boolean isDestroyed( )

Tests if this thread group has been 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.


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.


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 MIN_PRIORITY or greater than 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.


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.


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.

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 determines if the Throwable argument is an instance of ThreadDeath. If so, nothing special is done. Otherwise, the Throwable's printStackTrace method is called to print a stack backtrace to the standard error stream.

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



Known Subclasses
 
None.



 
 
  dydoc
  3/10/05