public ThreadGroup(String name) 
{
        this(Thread.currentThread().getThreadGroup(), 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.

Throws:

SecurityException - if the current thread cannot create a thread in the specified thread group.

Also see:

java.lang.ThreadGroup#checkAccess()
exception: SecurityException - if the current thread cannot create a thread in the specified thread group.

since: JDK1.0 -

 public ThreadGroup(ThreadGroup parent,
    String name) 
{
        this(checkParentAccess(parent), parent, 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.

Throws:

NullPointerException - if the thread group argument is null.

SecurityException - if the current thread cannot create a thread in the specified thread group.

Also see:

java.lang.SecurityException
java.lang.ThreadGroup#checkAccess()
exception: NullPointerException - if the thread group argument is null.

exception: SecurityException - if the current thread cannot create a thread in the specified thread group.

since: JDK1.0 -

 public int activeCount() 
{
        int result;
        // Snapshot sub-group data so we don't hold this lock
        // while our children are computing.
        int ngroupsSnapshot;
        ThreadGroup[] groupsSnapshot;
        synchronized (this) {
            if (destroyed) {
                return 0;
            }
            result = nthreads;
            ngroupsSnapshot = ngroups;
            if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
            } else {
                groupsSnapshot = null;
            }
        }
        for (int i = 0 ; i <  ngroupsSnapshot ; i++) {
            result += groupsSnapshot[i].activeCount();
        }
        return result;
}

Returns an estimate of the number of active threads 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 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.

 public int activeGroupCount() 
{
        int ngroupsSnapshot;
        ThreadGroup[] groupsSnapshot;
        synchronized (this) {
            if (destroyed) {
                return 0;
            }
            ngroupsSnapshot = ngroups;
            if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
            } else {
                groupsSnapshot = null;
            }
        }
        int n = ngroupsSnapshot;
        for (int i = 0 ; i <  ngroupsSnapshot ; i++) {
            n += groupsSnapshot[i].activeGroupCount();
        }
        return n;
}

Returns an estimate of the number of active 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.

  void add(Thread t) 
{
        synchronized (this) {
            if (destroyed) {
                throw new IllegalThreadStateException();
            }
            if (threads == null) {
                threads = new Thread[4];
            } else if (nthreads == threads.length) {
                threads = Arrays.copyOf(threads, nthreads * 2);
            }
            threads[nthreads] = t;
            // This is done last so it doesn't matter in case the
            // thread is killed
            nthreads++;
            // The thread is now a fully fledged member of the group, even
            // though it may, or may not, have been started yet. It will prevent
            // the group from being destroyed so the unstarted Threads count is
            // decremented.
            nUnstartedThreads--;
        }
}

Adds the specified thread to this thread group.

Note: This method is called from both library code and the Virtual Machine. It is called from VM to add certain system threads to the system thread group.

  void addUnstarted() 
{
        synchronized(this) {
            if (destroyed) {
                throw new IllegalThreadStateException();
            }
            nUnstartedThreads++;
        }
}

Increments the count of unstarted threads in the thread group. Unstarted threads are not added to the thread group so that they can be collected if they are never started, but they must be counted so that daemon thread groups with unstarted threads in them are not destroyed.

 public boolean allowThreadSuspension(boolean b) 
{
        this.vmAllowSuspension = b;
        if (!b) {
            VM.unsuspendSomeThreads();
        }
        return true;
}

Used by VM to control lowmem implicit suspension.

 public final  void checkAccess() 
{
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkAccess(this);
        }
}

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.

 public final  void destroy() 
{
        int ngroupsSnapshot;
        ThreadGroup[] groupsSnapshot;
        synchronized (this) {
            checkAccess();
            if (destroyed || (nthreads  > 0)) {
                throw new IllegalThreadStateException();
            }
            ngroupsSnapshot = ngroups;
            if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
            } else {
                groupsSnapshot = null;
            }
            if (parent != null) {
                destroyed = true;
                ngroups = 0;
                groups = null;
                nthreads = 0;
                threads = null;
            }
        }
        for (int i = 0 ; i <  ngroupsSnapshot ; i += 1) {
            groupsSnapshot[i].destroy();
        }
        if (parent != null) {
            parent.remove(this);
        }
}

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.

 public int enumerate(Thread[] list) 
{
        checkAccess();
        return enumerate(list, 0, true);
}

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

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

{@linkplain #enumerate(Thread[], boolean) enumerate}{@code (list, true)}

 public int enumerate(ThreadGroup[] list) 
{
        checkAccess();
        return enumerate(list, 0, true);
}

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

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

{@linkplain #enumerate(ThreadGroup[], boolean) enumerate}{@code (list, true)}

 public int enumerate(Thread[] list,
    boolean recurse) 
{
        checkAccess();
        return enumerate(list, 0, recurse);
}

Copies into the specified array every active thread in this thread group. If {@code recurse} is {@code true}, this method recursively enumerates all subgroups of this thread group and references to every active 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 {@linkplain #activeCount 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 {@code list}.

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

 public int enumerate(ThreadGroup[] list,
    boolean recurse) 
{
        checkAccess();
        return enumerate(list, 0, recurse);
}

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

An application might use the {@linkplain #activeGroupCount 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 {@code list}.

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

 public final int getMaxPriority() 
{
        return maxPriority;
}

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

 public final String getName() 
{
        return name;
}

Returns the name of this thread group.

 public final ThreadGroup getParent() 
{
        if (parent != null)
            parent.checkAccess();
        return parent;
}

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.

 public final  void interrupt() 
{
        int ngroupsSnapshot;
        ThreadGroup[] groupsSnapshot;
        synchronized (this) {
            checkAccess();
            for (int i = 0 ; i <  nthreads ; i++) {
                threads[i].interrupt();
            }
            ngroupsSnapshot = ngroups;
            if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
            } else {
                groupsSnapshot = null;
            }
        }
        for (int i = 0 ; i <  ngroupsSnapshot ; i++) {
            groupsSnapshot[i].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.

 public final boolean isDaemon() 
{
        return daemon;
}

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.

 public synchronized boolean isDestroyed() 
{
        return destroyed;
}

Tests if this thread group has been destroyed.

 public  void list() 
{
        list(System.out, 0);
}

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

  void list(PrintStream out,
    int indent) 
{
        int ngroupsSnapshot;
        ThreadGroup[] groupsSnapshot;
        synchronized (this) {
            for (int j = 0 ; j <  indent ; j++) {
                out.print(" ");
            }
            out.println(this);
            indent += 4;
            for (int i = 0 ; i <  nthreads ; i++) {
                for (int j = 0 ; j <  indent ; j++) {
                    out.print(" ");
                }
                out.println(threads[i]);
            }
            ngroupsSnapshot = ngroups;
            if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
            } else {
                groupsSnapshot = null;
            }
        }
        for (int i = 0 ; i <  ngroupsSnapshot ; i++) {
            groupsSnapshot[i].list(out, indent);
        }
}

 public final boolean parentOf(ThreadGroup g) 
{
        for (; g != null ; g = g.parent) {
            if (g == this) {
                return true;
            }
        }
        return false;
}

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

 public final  void resume() 
{
        int ngroupsSnapshot;
        ThreadGroup[] groupsSnapshot;
        synchronized (this) {
            checkAccess();
            for (int i = 0 ; i <  nthreads ; i++) {
                threads[i].resume();
            }
            ngroupsSnapshot = ngroups;
            if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
            } else {
                groupsSnapshot = null;
            }
        }
        for (int i = 0 ; i <  ngroupsSnapshot ; i++) {
            groupsSnapshot[i].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.

 public final  void setDaemon(boolean daemon) 
{
        checkAccess();
        this.daemon = 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.

 public final  void setMaxPriority(int pri) 
{
        int ngroupsSnapshot;
        ThreadGroup[] groupsSnapshot;
        synchronized (this) {
            checkAccess();
            if (pri <  Thread.MIN_PRIORITY || pri  > Thread.MAX_PRIORITY) {
                return;
            }
            maxPriority = (parent != null) ? Math.min(pri, parent.maxPriority) : pri;
            ngroupsSnapshot = ngroups;
            if (groups != null) {
                groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
            } else {
                groupsSnapshot = null;
            }
        }
        for (int i = 0 ; i <  ngroupsSnapshot ; i++) {
            groupsSnapshot[i].setMaxPriority(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 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.

 public final  void stop() 
{
        if (stopOrSuspend(false))
            Thread.currentThread().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.

 public final  void suspend() 
{
        if (stopOrSuspend(true))
            Thread.currentThread().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.

  void threadStartFailed(Thread t) 
{
        synchronized(this) {
            remove(t);
            nUnstartedThreads++;
        }
}

Notifies the group that the thread {@code t} has failed an attempt to start.

The state of this thread group is rolled back as if the attempt to start the thread has never occurred. The thread is again considered an unstarted member of the thread group, and a subsequent attempt to start the thread is permitted.

  void threadTerminated(Thread t) 
{
        synchronized (this) {
            remove(t);
            if (nthreads == 0) {
                notifyAll();
            }
            if (daemon && (nthreads == 0) &&
                (nUnstartedThreads == 0) && (ngroups == 0))
            {
                destroy();
            }
        }
}

Notifies the group that the thread {@code t} has terminated.

Destroy the group if all of the following conditions are true: this is a daemon thread group; there are no more alive or unstarted threads in the group; there are no subgroups in this thread group.

 public String toString() 
{
        return getClass().getName() + "[name=" + getName() + ",maxpri=" + maxPriority + "]";
}

Returns a string representation of this Thread group.

 public  void uncaughtException(Thread t,
    Throwable e) 
{
        if (parent != null) {
            parent.uncaughtException(t, e);
        } else {
            Thread.UncaughtExceptionHandler ueh =
                Thread.getDefaultUncaughtExceptionHandler();
            if (ueh != null) {
                ueh.uncaughtException(t, e);
            } else if (!(e instanceof ThreadDeath)) {
                System.err.print("Exception in thread \""
                                 + t.getName() + "\" ");
                e.printStackTrace(System.err);
            }
        }
}

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 {@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 ThreadDeath . If so, nothing special is done. 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 {@linkplain System#err standard error stream}.

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