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+/*
+
+Copyright (c) Xerox Corporation 1998-2002.  All rights reserved.
+
+Use and copying of this software and preparation of derivative works based
+upon this software are permitted.  Any distribution of this software or
+derivative works must comply with all applicable United States export control
+laws.
+
+This software is made available AS IS, and Xerox Corporation makes no warranty
+about the software, its performance or its conformity to any specification.
+
+|<---            this code is formatted to fit into 80 columns             --->|
+|<---            this code is formatted to fit into 80 columns             --->|
+|<---            this code is formatted to fit into 80 columns             --->|
+
+
+RegistrySynchronization.java
+Part of the Spacewar system.
+
+*/
+
+package spacewar;
+
+import coordination.Coordinator;
+
+
+/**
+ * This aspect ensures synchronized access to methods of the Registry in
+ * the presence of several threads.
+ *
+ * It uses the Coordinator class, from the AspectJ coordination library.
+ *
+ * It uses a per-Registry coordination scheme, so there is one instance of
+ * this class for each instance of the Registry class.  When this class is
+ * constructed, it registers appropriate mutexes and selfexes using the
+ * behavior inherited from Coordinator.
+ *
+ * The mutating methods (register and unregister) should be self-exclusive.
+ * Each reader method should be mutually exclusive with the mutating
+ * methods.  But the readers can run concurrently.  */
+aspect RegistrySynchronization extends Coordinator perthis(this(Registry)) {
+
+    protected pointcut synchronizationPoint():
+        call(void Registry.register(..))   ||
+        call(void Registry.unregister(..)) ||
+        call(SpaceObject[] Registry.getObjects(..)) ||
+        call(Ship[] Registry.getShips(..));
+    
+    public RegistrySynchronization() {
+        addSelfex("register");
+        addSelfex("unregister");
+
+        addMutex(new String[] {"register", "unregister", "getObjects"});
+        addMutex(new String[] {"register", "unregister", "getShips"});
+    }
+
+}