zdm/event-bus
zdm/event-bus
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Allow nested dispatches by keeping track of nesting count

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This commit is contained in:
Kai S. K. Engelbart 2021-07-12 10:19:04 +02:00
parent 74447dea59
commit 205a183db7
Signed by: kske
GPG Key ID: 8BEB13EC5DF7EF13
1 changed files with 22 additions and 6 deletions
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28
event-bus-core/src/main/java/dev/kske/eventbus/core/EventBus.java
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@ -27,7 +27,21 @@ public final class EventBus {
*/ */
private static final class DispatchState { 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); Objects.requireNonNull(event);
logger.log(Level.INFO, "Dispatching event {0}", event); logger.log(Level.INFO, "Dispatching event {0}", event);
// Set dispatch state // Look up dispatch state
var state = dispatchState.get(); var state = dispatchState.get();
state.isDispatching = true;
// Increment nesting count (becomes > 1 during nested dispatches)
++state.nestingCount;
Iterator<EventHandler> handlers = getHandlersFor(event.getClass()); Iterator<EventHandler> handlers = getHandlersFor(event.getClass());
if (handlers.hasNext()) { if (handlers.hasNext()) {
@ -118,8 +134,8 @@ public final class EventBus {
dispatch(new DeadEvent(this, event)); dispatch(new DeadEvent(this, event));
} }
// Reset dispatch state // Decrement nesting count (becomes 0 when all dispatches on the thread are finished)
state.isDispatching = false; --state.nestingCount;
logger.log(Level.DEBUG, "Finished dispatching event {0}", event); logger.log(Level.DEBUG, "Finished dispatching event {0}", event);
} }
@ -155,7 +171,7 @@ public final class EventBus {
*/ */
public void cancel() { public void cancel() {
var state = dispatchState.get(); var state = dispatchState.get();
if (state.isDispatching && !state.isCancelled) if (state.nestingCount > 0 && !state.isCancelled)
state.isCancelled = true; state.isCancelled = true;
else else
throw new EventBusException("Calling thread not an active dispatching thread!"); throw new EventBusException("Calling thread not an active dispatching thread!");