1 /*
   2  * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package sun.misc;
  27 
  28 import java.util.concurrent.locks.ReentrantLock;
  29 
  30 /**
  31  * This class is used to prevent multiple calling of g_thread_init ()
  32  * and gdk_thread_init ().
  33  *
  34  * Since version 2.24 of GLib, calling g_thread_init () multiple times is
  35  * allowed, but it will crash for older versions. There are two ways to 
  36  * find out if g_thread_init () has been called:
  37  * g_thread_get_initialized (), but it was introduced in 2.20
  38  * g_thread_supported (), but it is a macro and cannot be loaded with dlsym.
  39  *
  40  * usage:
  41  * <pre>
  42  * lock();
  43  * try {
  44  *    if (!getAndSetInitializationNeededFlag()) {
  45  *        //call to g_thread_init();
  46  *        //call to gdk_thread_init();
  47  *    }
  48  * } finally {
  49  *    unlock();
  50  * }
  51  * </pre>
  52  */
  53 public final class GThreadHelper {
  54 
  55     private static final ReentrantLock LOCK = new ReentrantLock();
  56     private static boolean isGThreadInitialized = false;
  57 
  58     /**
  59      * Acquires the lock.
  60      */
  61     public static void lock() {
  62         LOCK.lock();
  63     }
  64 
  65     /**
  66      * Releases the lock.
  67      */
  68     public static void unlock() {
  69         LOCK.unlock();
  70     }
  71 
  72     /**
  73      * Gets current value of initialization flag and sets it to {@code true}.
  74      * MUST be called under the lock.
  75      * 
  76      * A return value of {@code false} indicates that the calling code
  77      * should call the g_thread_init() and gdk_thread_init() functions
  78      * before releasing the lock.
  79      *
  80      * @return {@code true} if initialization has been completed.
  81      */
  82     public static boolean getAndSetInitializationNeededFlag() {
  83         boolean ret = isGThreadInitialized;
  84         isGThreadInitialized = true;
  85         return ret;
  86     }
  87 }