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Provides common I/O components.
There is a newer version: 2.5.0
/*
 * Copyright (C) 2012 Schlichtherle IT Services.
 * All rights reserved. Use is subject to license terms.
 */
package net.java.truecommons.io;

import javax.annotation.concurrent.Immutable;

/**
 * Static utility methods for {@link ThreadGroup}s.
 * 
 * @author Christian Schlichtherle
 */
@Immutable
final class ThreadGroups {

    /* Can't touch this - hammer time! */
    private ThreadGroups() { }

    /**
     * Returns the thread group of the
     * {@link System#getSecurityManager() security manager} if installed or
     * else the thread group of the current thread.
     * 
     * @return The thread group of the
     *         {@link System#getSecurityManager() security manager} if
     *         installed or else the thread group of the current thread.
     */
    public static ThreadGroup getThreadGroup() {
        final SecurityManager sm = System.getSecurityManager();
        return null != sm
                ? sm.getThreadGroup()
                : Thread.currentThread().getThreadGroup();
    }

    /**
     * Determines a suitable thread group for server threads which
     * provide shared services for one or more otherwise unrelated
     * client threads.
     * 
     * When a server thread gets spawned from a client thread and no particular
     * thread group is selected, then it gets inherited from the client thread
     * to the server thread.
     * However, this may be inappropriate if the server thread has a longer
     * life time than the client thread or if it's shared by other client
     * threads in different thread groups.
     * This method can then get used in order to determine a suitable thread
     * group for the server thread.
     * 
     * This method searches for the top level accessible parent thread group by
     * calling {@link #getThreadGroup()} and walking up the parent thread group
     * hierarchy until the next parent does not exist or is inaccessible.
     * If there is a security manager installed, then this method typically
     * returns its directly associated thread group because this is the only
     * accessible one.
     * Otherwise, this method typically returns the root thread group.
     * 
     * @return The result of the search for the top level accessible parent
     *         thread group, starting with the thread group of the security
     *         manager if installed or else the thread group of the current
     *         thread and walking up the parent thread group hierarchy until
     *         the next parent does not exist or is inaccessible.
     */
    public static ThreadGroup getServerThreadGroup() {
        ThreadGroup tg = getThreadGroup();
        for (ThreadGroup ntg; null != (ntg = tg.getParent()); tg = ntg) {
            try {
                ntg.checkAccess();
            } catch (SecurityException ex) {
                break;
            }
        }
        return tg;
    }
}