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Merge pull request 'Properly Handle Nested Dispatches' (#19) from b/nested-dispatch into develop

Reviewed-on: https://git.kske.dev/kske/event-bus/pulls/19
Reviewed-by: delvh <leon@kske.dev>
develop
kske 3 weeks ago
parent
commit
b915a5c490
Signed by: KSKE Git GPG Key ID: 70F2F9206EDC1FCE
  1. 38
      event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java
  2. 73
      event-bus-core/src/test/java/dev/kske/eventbus/core/NestedTest.java

38
event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java

@ -27,7 +27,21 @@ public final class EventBus {
*/
private static final class DispatchState {
boolean isDispatching, isCancelled;
/**
* Indicates that the last event handler invoked has called {@link EventBus#cancel}. In that
* case, the event is not dispatched further.
*
* @since 0.1.0
*/
boolean isCancelled;
/**
* Is incremented when {@link EventBus#dispatch(Object)} is invoked and decremented when it
* finishes. This allows keeping track of nested dispatches.
*
* @since 1.2.0
*/
int nestingCount;
}
/**
@ -79,9 +93,11 @@ public final class EventBus {
Objects.requireNonNull(event);
logger.log(Level.INFO, "Dispatching event {0}", event);
// Set dispatch state
// Look up dispatch state
var state = dispatchState.get();
state.isDispatching = true;
// Increment nesting count (becomes > 1 during nested dispatches)
++state.nestingCount;
Iterator<EventHandler> handlers = getHandlersFor(event.getClass());
if (handlers.hasNext()) {
@ -94,14 +110,14 @@ public final class EventBus {
try {
handlers.next().execute(event);
} catch (InvocationTargetException e) {
if (event instanceof DeadEvent || event instanceof ExceptionEvent)
// Warn about system event not being handled
logger.log(Level.WARNING, event + " not handled due to exception", e);
else if (e.getCause() instanceof Error)
if (e.getCause() instanceof Error)
// Transparently pass error to the caller
throw (Error) e.getCause();
else if (event instanceof DeadEvent || event instanceof ExceptionEvent)
// Warn about system event not being handled
logger.log(Level.WARNING, event + " not handled due to exception", e);
else
// Dispatch exception event
@ -118,8 +134,8 @@ public final class EventBus {
dispatch(new DeadEvent(this, event));
}
// Reset dispatch state
state.isDispatching = false;
// Decrement nesting count (becomes 0 when all dispatches on the thread are finished)
--state.nestingCount;
logger.log(Level.DEBUG, "Finished dispatching event {0}", event);
}
@ -155,7 +171,7 @@ public final class EventBus {
*/
public void cancel() {
var state = dispatchState.get();
if (state.isDispatching && !state.isCancelled)
if (state.nestingCount > 0 && !state.isCancelled)
state.isCancelled = true;
else
throw new EventBusException("Calling thread not an active dispatching thread!");

73
event-bus-core/src/test/java/dev/kske/eventbus/core/NestedTest.java

@ -0,0 +1,73 @@
package dev.kske.eventbus.core;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.*;
/**
* Tests nested event dispatches.
*
* @author Kai S. K. Engelbart
* @since 1.2.0
*/
class NestedTest {
EventBus bus;
boolean nestedHit;
/**
* Constructs an event bus and registers this test instance as an event listener.
*
* @since 1.2.0
*/
@BeforeEach
void registerListener() {
bus = new EventBus();
bus.registerListener(this);
}
/**
* Dispatches a simple event, which should in turn cause a string to be dispatched as a nested
* event. If the corresponding handler sets {@link #nestedHit} to {@code true}, the test is
* successful.
*
* @since 1.2.0
*/
@Test
void testNestedDispatch() {
bus.dispatch(new SimpleEvent());
assertTrue(nestedHit);
}
/**
* Dispatches a string as a nested event and cancels the current dispatch afterwards.
*
* @since 1.2.0
*/
@Event(SimpleEvent.class)
void onSimpleEvent() {
bus.dispatch("Nested event");
bus.cancel();
}
/**
* Sets {@link #nestedHit} to {@code true} indicating that nested dispatches work.
*
* @since 1.2.0
*/
@Event(String.class)
void onString() {
nestedHit = true;
}
/**
* Fails the test if an exception is caused during the dispatch.
*
* @param e the event containing the exception
* @since 1.2.0
*/
@Event
void onException(ExceptionEvent e) {
fail("Exception during dispatch", e.getCause());
}
}
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