public void fire(
DependentSubjectListener subject, Integer event, DependentSubjectListener listener) {
// update the listener
boolean incremented = listener.latestRevision < event.intValue();
listener.latestRevision = event.intValue();
// make sure the listener's dependencies were notified first
listener.assertDependenciesSatisfiedRecursively(listener);
// send the event forward
if (incremented) {
listener.increment(0);
}
}
/**
* Prepare the original diamond-dependency problem, where B depends on A and C depends on both A
* and B. We need to guarantee that C can read all of its dependencies only when they're in a
* 'consistent' state, which is when they've received all events from their dependencies, and
* their dependencies are in a consistent state.
*
* <p>A --> B --. This diagram shows A --> B, B --> C and A --> C. | | The only safe notification
* order of events is | V for B to receive events from A before C receives '-------> C those same
* events.
*/
public void testDiamondDependency() {
SequenceDependenciesEventPublisher publisher = new SequenceDependenciesEventPublisher();
DependentSubjectListener a = new DependentSubjectListener("A", publisher);
DependentSubjectListener b = new DependentSubjectListener("B", publisher);
DependentSubjectListener c = new DependentSubjectListener("C", publisher);
a.addListener(c);
a.increment(10);
assertEquals(10, a.latestRevision);
assertEquals(0, b.latestRevision);
assertEquals(10, c.latestRevision);
c.increment(5);
assertEquals(10, a.latestRevision);
assertEquals(0, b.latestRevision);
assertEquals(15, c.latestRevision);
b.increment(20);
assertEquals(10, a.latestRevision);
assertEquals(20, b.latestRevision);
assertEquals(15, c.latestRevision);
b.addListener(c);
assertEquals(10, a.latestRevision);
assertEquals(20, b.latestRevision);
assertEquals(20, c.latestRevision);
b.increment(2);
assertEquals(10, a.latestRevision);
assertEquals(22, b.latestRevision);
assertEquals(22, c.latestRevision);
a.increment(15);
assertEquals(25, a.latestRevision);
assertEquals(22, b.latestRevision);
assertEquals(25, c.latestRevision);
a.addListener(b);
assertEquals(25, a.latestRevision);
assertEquals(25, b.latestRevision);
assertEquals(25, c.latestRevision);
a.increment(4);
assertEquals(29, a.latestRevision);
assertEquals(29, b.latestRevision);
assertEquals(29, c.latestRevision);
}