1 /*
   2  * Copyright (c) 2007, 2008, 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.awt.image;
  27 
  28 import java.awt.image.BufferStrategy;
  29 import java.lang.ref.WeakReference;
  30 
  31 /**
  32  * Manages v-synced buffer strategies.
  33  */
  34 public abstract class VSyncedBSManager {
  35 
  36     private static VSyncedBSManager theInstance;
  37 
  38     private static final boolean vSyncLimit =
  39         Boolean.valueOf((String)java.security.AccessController.doPrivileged(
  40                 new sun.security.action.GetPropertyAction(
  41                     "sun.java2d.vsynclimit", "true")));
  42 
  43     private static VSyncedBSManager getInstance(boolean create) {
  44         if (theInstance == null && create) {
  45             theInstance =
  46                 vSyncLimit ? new SingleVSyncedBSMgr() : new NoLimitVSyncBSMgr();
  47         }
  48         return theInstance;
  49     }
  50 
  51     abstract boolean checkAllowed(BufferStrategy bs);
  52     abstract void relinquishVsync(BufferStrategy bs);
  53 
  54     /**
  55      * Returns true if the buffer strategy is allowed to be created
  56      * v-synced.
  57      *
  58      * @return true if the bs is allowed to be v-synced, false otherwise
  59      */
  60     public static boolean vsyncAllowed(BufferStrategy bs) {
  61         VSyncedBSManager bsm = getInstance(true);
  62         return bsm.checkAllowed(bs);
  63     }
  64 
  65     /**
  66      * Lets the manager know that this buffer strategy is no longer interested
  67      * in being v-synced.
  68      */
  69     public static synchronized void releaseVsync(BufferStrategy bs) {
  70         VSyncedBSManager bsm = getInstance(false);
  71         if (bsm != null) {
  72             bsm.relinquishVsync(bs);
  73         }
  74     }
  75 
  76     /**
  77      * An instance of the manager which allows any buffer strategy to be
  78      * v-synced.
  79      */
  80     private static final class NoLimitVSyncBSMgr extends VSyncedBSManager {
  81         @Override
  82         boolean checkAllowed(BufferStrategy bs) {
  83             return true;
  84         }
  85 
  86         @Override
  87         void relinquishVsync(BufferStrategy bs) {
  88         }
  89     }
  90 
  91     /**
  92      * An instance of the manager which allows only one buffer strategy to
  93      * be v-synced at any give moment in the vm.
  94      */
  95     private static final class SingleVSyncedBSMgr extends VSyncedBSManager {
  96         private WeakReference<BufferStrategy> strategy;
  97 
  98         @Override
  99         public synchronized boolean checkAllowed(BufferStrategy bs) {
 100             if (strategy != null) {
 101                 BufferStrategy current = strategy.get();
 102                 if (current != null) {
 103                     return (current == bs);
 104                 }
 105             }
 106             strategy = new WeakReference<BufferStrategy>(bs);
 107             return true;
 108         }
 109 
 110         @Override
 111         public synchronized void relinquishVsync(BufferStrategy bs) {
 112             if (strategy != null) {
 113                 BufferStrategy b = strategy.get();
 114                 if (b == bs) {
 115                     strategy.clear();
 116                     strategy = null;
 117                 }
 118             }
 119         }
 120     }
 121 }