Java example source code file (GThreadHelper.java)

This example Java source code file (GThreadHelper.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

gthreadhelper, lock, reentrantlock

The GThreadHelper.java Java example source code

/*
 * Copyright (c) 2013, 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 sun.misc;

import java.util.concurrent.locks.ReentrantLock;

/**
 * This class is used to prevent multiple calling of g_thread_init ()
 * and gdk_thread_init ().
 *
 * Since version 2.24 of GLib, calling g_thread_init () multiple times is
 * allowed, but it will crash for older versions. There are two ways to
 * find out if g_thread_init () has been called:
 * g_thread_get_initialized (), but it was introduced in 2.20
 * g_thread_supported (), but it is a macro and cannot be loaded with dlsym.
 *
 * usage:
 * <pre>
 * lock();
 * try {
 *    if (!getAndSetInitializationNeededFlag()) {
 *        //call to g_thread_init();
 *        //call to gdk_thread_init();
 *    }
 * } finally {
 *    unlock();
 * }
 * </pre>
 */
public final class GThreadHelper {

    private static final ReentrantLock LOCK = new ReentrantLock();
    private static boolean isGThreadInitialized = false;

    /**
     * Acquires the lock.
     */
    public static void lock() {
        LOCK.lock();
    }

    /**
     * Releases the lock.
     */
    public static void unlock() {
        LOCK.unlock();
    }

    /**
     * Gets current value of initialization flag and sets it to {@code true}.
     * MUST be called under the lock.
     *
     * A return value of {@code false} indicates that the calling code
     * should call the g_thread_init() and gdk_thread_init() functions
     * before releasing the lock.
     *
     * @return {@code true} if initialization has been completed.
     */
    public static boolean getAndSetInitializationNeededFlag() {
        boolean ret = isGThreadInitialized;
        isGThreadInitialized = true;
        return ret;
    }
}