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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(java.security.AccessController.doPrivileged(
40                 new sun.security.action.GetPropertyAction(
41                     "sun.java2d.vsynclimit", "true")));
42 
getInstance(boolean create)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 
checkAllowed(BufferStrategy bs)51     abstract boolean checkAllowed(BufferStrategy bs);
relinquishVsync(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      */
vsyncAllowed(BufferStrategy bs)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      */
releaseVsync(BufferStrategy bs)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
checkAllowed(BufferStrategy bs)82         boolean checkAllowed(BufferStrategy bs) {
83             return true;
84         }
85 
86         @Override
relinquishVsync(BufferStrategy bs)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
checkAllowed(BufferStrategy bs)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
relinquishVsync(BufferStrategy bs)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 }
122