src/java.desktop/share/classes/sun/awt/util/ThreadGroupUtils.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package sun.awt.util;

/**
 * A utility class needed to access the root {@code ThreadGroup}
 *
 * The class should not depend on any others, because it' called from JNI_OnLoad of the AWT
 * native library. Triggering class loading could lead to a deadlock.
 */
public final class ThreadGroupUtils {

    private ThreadGroupUtils() {
        // Avoid instantiation
    }

    /**
     * Returns a root thread group.
     *
     * @return a root {@code ThreadGroup}
     */
    public static ThreadGroup getRootThreadGroup() {
        ThreadGroup currentTG = Thread.currentThread().getThreadGroup();
        ThreadGroup parentTG = currentTG.getParent();
        while (parentTG != null) {
            currentTG = parentTG;
            parentTG = currentTG.getParent();
        }
        return currentTG;
    }
}