1 public class Bus {
 2   public static final String DEFAULT_IDENTIFIER = "default";
 3 
 4   /** All registered event handlers, indexed by event type. */
 5   private final ConcurrentMap<Class<?>, Set<EventHandler>> handlersByType =
 6           new ConcurrentHashMap<Class<?>, Set<EventHandler>>();
 7 
 8   /** All registered event producers, index by event type. */
 9   private final ConcurrentMap<Class<?>, EventProducer> producersByType =
10           new ConcurrentHashMap<Class<?>, EventProducer>();
11 
12   /** Identifier used to differentiate the event bus instance. */
13   private final String identifier;
14 
15   /** Thread enforcer for register, unregister, and posting events. */
16   private final ThreadEnforcer enforcer;
17 
18   /** Used to find handler methods in register and unregister. */
19   private final HandlerFinder handlerFinder;
20 
21   /** Queues of events for the current thread to dispatch. */
22   private final ThreadLocal<ConcurrentLinkedQueue<EventWithHandler>> eventsToDispatch =
23       new ThreadLocal<ConcurrentLinkedQueue<EventWithHandler>>() {
24         @Override protected ConcurrentLinkedQueue<EventWithHandler> initialValue() {
25           return new ConcurrentLinkedQueue<EventWithHandler>();
26         }
27       };
28 
29   /** True if the current thread is currently dispatching an event. */
30   private final ThreadLocal<Boolean> isDispatching = new ThreadLocal<Boolean>() {
31     @Override protected Boolean initialValue() {
32       return false;
33     }
34   };
35 
36   /** Creates a new Bus named "default" that enforces actions on the main thread. */
37   public Bus() {
38     this(DEFAULT_IDENTIFIER);
39   }
40 
41   /**
42    * Creates a new Bus with the given {@code identifier} that enforces actions on the main thread.
43    *
44    * @param identifier a brief name for this bus, for debugging purposes.  Should be a valid Java identifier.
45    */
46   public Bus(String identifier) {
47     this(ThreadEnforcer.MAIN, identifier);
48   }
49 
50   /**
51    * Creates a new Bus named "default" with the given {@code enforcer} for actions.
52    *
53    * @param enforcer Thread enforcer for register, unregister, and post actions.
54    */
55   public Bus(ThreadEnforcer enforcer) {
56     this(enforcer, DEFAULT_IDENTIFIER);
57   }
58 
59   /**
60    * Creates a new Bus with the given {@code enforcer} for actions and the given {@code identifier}.
61    *
62    * @param enforcer Thread enforcer for register, unregister, and post actions.
63    * @param identifier A brief name for this bus, for debugging purposes.  Should be a valid Java identifier.
64    */
65   public Bus(ThreadEnforcer enforcer, String identifier) {
66     this(enforcer, identifier, HandlerFinder.ANNOTATED);
67   }
68 
69   /**
70    * Test constructor which allows replacing the default {@code HandlerFinder}.
71    *
72    * @param enforcer Thread enforcer for register, unregister, and post actions.
73    * @param identifier A brief name for this bus, for debugging purposes.  Should be a valid Java identifier.
74    * @param handlerFinder Used to discover event handlers and producers when registering/unregistering an object.
75    */
76   Bus(ThreadEnforcer enforcer, String identifier, HandlerFinder handlerFinder) {
77     this.enforcer =  enforcer;
78     this.identifier = identifier;
79     this.handlerFinder = handlerFinder;
80   }
81 
82   @Override public String toString() {
83     return "[Bus \"" + identifier + "\"]";
84   }