/*
 * 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;
    }
}