/* * Copyright (c) 1995, 2007, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.lang; import java.io.PrintStream; import java.util.Arrays; import sun.misc.VM; /** * 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. * * @author unascribed * @since JDK1.0 */ /* The locking strategy for this code is to try to lock only one level of the * tree wherever possible, but otherwise to lock from the bottom up. * That is, from child thread groups to parents. * This has the advantage of limiting the number of locks that need to be held * and in particular avoids having to grab the lock for the root thread group, * (or a global lock) which would be a source of contention on a * multi-processor system with many thread groups. * This policy often leads to taking a snapshot of the state of a thread group * and working off of that snapshot, rather than holding the thread group locked * while we work on the children. */ public class ThreadGroup implements Thread.UncaughtExceptionHandler { private final ThreadGroup parent; String name; int maxPriority; boolean destroyed; boolean daemon; boolean vmAllowSuspension; int nUnstartedThreads = 0; int nthreads; Thread threads[]; int ngroups; ThreadGroup groups[]; /** * Creates an empty Thread group that is not in any Thread group. * This method is used to create the system Thread group. */ private ThreadGroup() { // called from C code this.name = "system"; this.maxPriority = Thread.MAX_PRIORITY; this.parent = null; } /** * 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.
*
* @param name the name of the new thread group.
* @exception SecurityException if the current thread cannot create a
* thread in the specified thread group.
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
public ThreadGroup(String name) {
this(Thread.currentThread().getThreadGroup(), 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.
*
* @param parent the parent thread group.
* @param name the name of the new thread group.
* @exception NullPointerException if the thread group argument is
* null
.
* @exception SecurityException if the current thread cannot create a
* thread in the specified thread group.
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
public ThreadGroup(ThreadGroup parent, String name) {
this(checkParentAccess(parent), parent, name);
}
private ThreadGroup(Void unused, ThreadGroup parent, String name) {
this.name = name;
this.maxPriority = parent.maxPriority;
this.daemon = parent.daemon;
this.vmAllowSuspension = parent.vmAllowSuspension;
this.parent = parent;
parent.add(this);
}
/*
* @throws NullPointerException if the parent argument is {@code null}
* @throws SecurityException if the current thread cannot create a
* thread in the specified thread group.
*/
private static Void checkParentAccess(ThreadGroup parent) {
parent.checkAccess();
return null;
}
/**
* Returns the name of this thread group.
*
* @return the name of this thread group.
* @since JDK1.0
*/
public final String getName() {
return name;
}
/**
* 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.
*
* @return the parent of this thread group. The top-level thread group
* is the only thread group whose parent is null
.
* @exception SecurityException if the current thread cannot modify
* this thread group.
* @see java.lang.ThreadGroup#checkAccess()
* @see java.lang.SecurityException
* @see java.lang.RuntimePermission
* @since JDK1.0
*/
public final ThreadGroup getParent() {
if (parent != null)
parent.checkAccess();
return parent;
}
/**
* Returns the maximum priority of this thread group. Threads that are
* part of this group cannot have a higher priority than the maximum
* priority.
*
* @return the maximum priority that a thread in this thread group
* can have.
* @see #setMaxPriority
* @since JDK1.0
*/
public final int getMaxPriority() {
return maxPriority;
}
/**
* 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.
*
* @return true
if this thread group is a daemon thread group;
* false
otherwise.
* @since JDK1.0
*/
public final boolean isDaemon() {
return daemon;
}
/**
* Tests if this thread group has been destroyed.
*
* @return true if this object is destroyed
* @since JDK1.1
*/
public synchronized boolean isDestroyed() {
return destroyed;
}
/**
* 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.
*
* @param daemon if true
, marks this thread group as
* a daemon thread group; otherwise, marks this
* thread group as normal.
* @exception SecurityException if the current thread cannot modify
* this thread group.
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
public final void setDaemon(boolean daemon) {
checkAccess();
this.daemon = daemon;
}
/**
* 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.
*
* @param pri the new priority of the thread group.
* @exception SecurityException if the current thread cannot modify
* this thread group.
* @see #getMaxPriority
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
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);
}
}
/**
* Tests if this thread group is either the thread group
* argument or one of its ancestor thread groups.
*
* @param g a thread group.
* @return true
if this thread group is the thread group
* argument or one of its ancestor thread groups;
* false
otherwise.
* @since JDK1.0
*/
public final boolean parentOf(ThreadGroup g) {
for (; g != null ; g = g.parent) {
if (g == this) {
return true;
}
}
return false;
}
/**
* 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
.
*
* @exception SecurityException if the current thread is not allowed to
* access this thread group.
* @see java.lang.SecurityManager#checkAccess(java.lang.ThreadGroup)
* @since JDK1.0
*/
public final void checkAccess() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkAccess(this);
}
}
/**
* 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. * * @return 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 * * @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; } /** * 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)} ** * @param list * an array into which to put the list of threads * * @return the number of threads put into the array * * @throws SecurityException * if {@linkplain #checkAccess checkAccess} determines that * the current thread cannot access this thread group * * @since JDK1.0 */ public int enumerate(Thread list[]) { checkAccess(); return enumerate(list, 0, true); } /** * 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. * * @param list * an array into which to put the list of threads * * @param recurse * if {@code true}, recursively enumerate all subgroups of this * thread group * * @return the number of threads put into the array * * @throws SecurityException * if {@linkplain #checkAccess checkAccess} determines that * the current thread cannot access this thread group * * @since JDK1.0 */ public int enumerate(Thread list[], boolean recurse) { checkAccess(); return enumerate(list, 0, recurse); } private int enumerate(Thread list[], int n, boolean recurse) { int ngroupsSnapshot = 0; ThreadGroup[] groupsSnapshot = null; synchronized (this) { if (destroyed) { return 0; } int nt = nthreads; if (nt > list.length - n) { nt = list.length - n; } for (int i = 0; i < nt; i++) { if (threads[i].isAlive()) { list[n++] = threads[i]; } } if (recurse) { ngroupsSnapshot = ngroups; if (groups != null) { groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot); } else { groupsSnapshot = null; } } } if (recurse) { for (int i = 0 ; i < ngroupsSnapshot ; i++) { n = groupsSnapshot[i].enumerate(list, n, true); } } 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. * * @return the number of active thread groups with this thread group as * an ancestor * * @since JDK1.0 */ 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; } /** * 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)} ** * @param list * an array into which to put the list of thread groups * * @return the number of thread groups put into the array * * @throws SecurityException * if {@linkplain #checkAccess checkAccess} determines that * the current thread cannot access this thread group * * @since JDK1.0 */ 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. 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. * * @param list * an array into which to put the list of thread groups * * @param recurse * if {@code true}, recursively enumerate all subgroups * * @return the number of thread groups put into the array * * @throws SecurityException * if {@linkplain #checkAccess checkAccess} determines that * the current thread cannot access this thread group * * @since JDK1.0 */ public int enumerate(ThreadGroup list[], boolean recurse) { checkAccess(); return enumerate(list, 0, recurse); } private int enumerate(ThreadGroup list[], int n, boolean recurse) { int ngroupsSnapshot = 0; ThreadGroup[] groupsSnapshot = null; synchronized (this) { if (destroyed) { return 0; } int ng = ngroups; if (ng > list.length - n) { ng = list.length - n; } if (ng > 0) { System.arraycopy(groups, 0, list, n, ng); n += ng; } if (recurse) { ngroupsSnapshot = ngroups; if (groups != null) { groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot); } else { groupsSnapshot = null; } } } if (recurse) { for (int i = 0 ; i < ngroupsSnapshot ; i++) { n = groupsSnapshot[i].enumerate(list, n, true); } } return n; } /** * 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.
*
* @exception SecurityException if the current thread is not allowed
* to access this thread group or any of the threads in
* the thread group.
* @see java.lang.SecurityException
* @see java.lang.Thread#stop()
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
* @deprecated This method is inherently unsafe. See
* {@link Thread#stop} for details.
*/
@Deprecated
public final void stop() {
if (stopOrSuspend(false))
Thread.currentThread().stop();
}
/**
* 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.
*
* @exception SecurityException if the current thread is not allowed
* to access this thread group or any of the threads in
* the thread group.
* @see java.lang.Thread#interrupt()
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since 1.2
*/
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();
}
}
/**
* 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.
*
* @exception SecurityException if the current thread is not allowed
* to access this thread group or any of the threads in
* the thread group.
* @see java.lang.Thread#suspend()
* @see java.lang.SecurityException
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
* @deprecated This method is inherently deadlock-prone. See
* {@link Thread#suspend} for details.
*/
@Deprecated
public final void suspend() {
if (stopOrSuspend(true))
Thread.currentThread().suspend();
}
/**
* Helper method: recursively stops or suspends (as directed by the
* boolean argument) all of the threads in this thread group and its
* subgroups, except the current thread. This method returns true
* if (and only if) the current thread is found to be in this thread
* group or one of its subgroups.
*/
private boolean stopOrSuspend(boolean suspend) {
boolean suicide = false;
Thread us = Thread.currentThread();
int ngroupsSnapshot;
ThreadGroup[] groupsSnapshot = null;
synchronized (this) {
checkAccess();
for (int i = 0 ; i < nthreads ; i++) {
if (threads[i]==us)
suicide = true;
else if (suspend)
threads[i].suspend();
else
threads[i].stop();
}
ngroupsSnapshot = ngroups;
if (groups != null) {
groupsSnapshot = Arrays.copyOf(groups, ngroupsSnapshot);
}
}
for (int i = 0 ; i < ngroupsSnapshot ; i++)
suicide = groupsSnapshot[i].stopOrSuspend(suspend) || suicide;
return suicide;
}
/**
* 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.
*
* @exception SecurityException if the current thread is not allowed to
* access this thread group or any of the threads in the
* thread group.
* @see java.lang.SecurityException
* @see java.lang.Thread#resume()
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
* @deprecated This method is used solely in conjunction with
* Thread.suspend and ThreadGroup.suspend,
* both of which have been deprecated, as they are inherently
* deadlock-prone. See {@link Thread#suspend} for details.
*/
@Deprecated
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();
}
}
/**
* 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.
*
* @exception IllegalThreadStateException if the thread group is not
* empty or if the thread group has already been destroyed.
* @exception SecurityException if the current thread cannot modify this
* thread group.
* @see java.lang.ThreadGroup#checkAccess()
* @since JDK1.0
*/
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);
}
}
/**
* Adds the specified Thread group to this group.
* @param g the specified Thread group to be added
* @exception IllegalThreadStateException If the Thread group has been destroyed.
*/
private final void add(ThreadGroup g){
synchronized (this) {
if (destroyed) {
throw new IllegalThreadStateException();
}
if (groups == null) {
groups = new ThreadGroup[4];
} else if (ngroups == groups.length) {
groups = Arrays.copyOf(groups, ngroups * 2);
}
groups[ngroups] = g;
// This is done last so it doesn't matter in case the
// thread is killed
ngroups++;
}
}
/**
* Removes the specified Thread group from this group.
* @param g the Thread group to be removed
* @return if this Thread has already been destroyed.
*/
private void remove(ThreadGroup g) {
synchronized (this) {
if (destroyed) {
return;
}
for (int i = 0 ; i < ngroups ; i++) {
if (groups[i] == g) {
ngroups -= 1;
System.arraycopy(groups, i + 1, groups, i, ngroups - i);
// Zap dangling reference to the dead group so that
// the garbage collector will collect it.
groups[ngroups] = null;
break;
}
}
if (nthreads == 0) {
notifyAll();
}
if (daemon && (nthreads == 0) &&
(nUnstartedThreads == 0) && (ngroups == 0))
{
destroy();
}
}
}
/**
* 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.
*/
void addUnstarted() {
synchronized(this) {
if (destroyed) {
throw new IllegalThreadStateException();
}
nUnstartedThreads++;
}
}
/**
* Notifies the group that the thread {@code t} is about to be
* started and adds the thread to this thread group.
*
* The thread is now a fully fledged member of the group, even though
* it hasn't been started yet. It will prevent the group from being
* destroyed so the unstarted Threads count is decremented.
*/
void threadStarting(Thread t) {
synchronized (this) {
add(t);
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. * * @param t * the Thread to be added * * @throws IllegalThreadStateException * if the Thread group has been destroyed */ 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++; } } /** * 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. * * @param t * the Thread whose start method was invoked * * @param failed * true if the thread could not be started successfully */ void threadStartFailed(Thread t) { synchronized(this) { remove(t); nUnstartedThreads++; } } /** * 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. * * @param t * the Thread that has terminated */ void threadTerminated(Thread t) { synchronized (this) { remove(t); if (nthreads == 0) { notifyAll(); } if (daemon && (nthreads == 0) && (nUnstartedThreads == 0) && (ngroups == 0)) { destroy(); } } } /** * Removes the specified Thread from this group. Invoking this method * on a thread group that has been destroyed has no effect. * * @param t * the Thread to be removed */ private void remove(Thread t) { synchronized (this) { if (destroyed) { return; } for (int i = 0 ; i < nthreads ; i++) { if (threads[i] == t) { System.arraycopy(threads, i + 1, threads, i, --nthreads - i); // Zap dangling reference to the dead thread so that // the garbage collector will collect it. threads[nthreads] = null; break; } } } } /** * Prints information about this thread group to the standard * output. This method is useful only for debugging. * * @since JDK1.0 */ public void list() { list(System.out, 0); } 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); } } /** * 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:
*
uncaughtException
method of that parent is called
* with the same two arguments.
* uncaughtException
method is called with the same
* two arguments.
* 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.
*
* @param t the thread that is about to exit.
* @param e the uncaught exception.
* @since JDK1.0
*/
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);
}
}
}
/**
* Used by VM to control lowmem implicit suspension.
*
* @param b boolean to allow or disallow suspension
* @return true on success
* @since JDK1.1
* @deprecated The definition of this call depends on {@link #suspend},
* which is deprecated. Further, the behavior of this call
* was never specified.
*/
@Deprecated
public boolean allowThreadSuspension(boolean b) {
this.vmAllowSuspension = b;
if (!b) {
VM.unsuspendSomeThreads();
}
return true;
}
/**
* Returns a string representation of this Thread group.
*
* @return a string representation of this thread group.
* @since JDK1.0
*/
public String toString() {
return getClass().getName() + "[name=" + getName() + ",maxpri=" + maxPriority + "]";
}
}