Broadcast events asynchronously.

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseComponentImpl.java

@@ -160,13 +160,15 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	public void endTransaction(Transaction transaction) {
 		try {
 			T txn = txnClass.cast(transaction.unbox());
-			if (!transaction.isCommitted()) db.abortTransaction(txn);
+			if (transaction.isCommitted()) {
+				for (Event e : transaction.getEvents()) eventBus.broadcast(e);
+			} else {
+				db.abortTransaction(txn);
+			}
 		} finally {
 			if (transaction.isReadOnly()) lock.readLock().unlock();
 			else lock.writeLock().unlock();
 		}
-		if (transaction.isCommitted())
-			for (Event e : transaction.getEvents()) eventBus.broadcast(e);
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/event/DefaultEventExecutorModule.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.event;
+
+import org.briarproject.bramble.api.event.EventExecutor;
+
+import java.util.concurrent.Executor;
+
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
+
+/**
+ * Default implementation of {@link EventExecutor} that uses a dedicated thread
+ * to notify listeners of events. Applications may prefer to supply an
+ * implementation that uses an existing thread, such as the UI thread.
+ */
+@Module
+public class DefaultEventExecutorModule {
+
+	@Provides
+	@Singleton
+	@EventExecutor
+	Executor provideEventExecutor() {
+		return newSingleThreadExecutor(r -> {
+			Thread t = new Thread(r);
+			t.setDaemon(true);
+			return t;
+		});
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/event/EventBusImpl.java

@@ -7,6 +7,7 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.util.Collection;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.Executor;
 
 import javax.annotation.concurrent.ThreadSafe;
 
@@ -16,6 +17,11 @@ class EventBusImpl implements EventBus {
 
 	private final Collection<EventListener> listeners =
 			new CopyOnWriteArrayList<>();
+	private final Executor eventExecutor;
+
+	EventBusImpl(Executor eventExecutor) {
+		this.eventExecutor = eventExecutor;
+	}
 
 	@Override
 	public void addListener(EventListener l) {
@@ -29,6 +35,8 @@ class EventBusImpl implements EventBus {
 
 	@Override
 	public void broadcast(Event e) {
-		for (EventListener l : listeners) l.eventOccurred(e);
+		eventExecutor.execute(() -> {
+			for (EventListener l : listeners) l.eventOccurred(e);
+		});
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/event/EventModule.java

@@ -1,6 +1,9 @@
 package org.briarproject.bramble.event;
 
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventExecutor;
+
+import java.util.concurrent.Executor;
 
 import javax.inject.Singleton;
 
@@ -12,7 +15,7 @@ public class EventModule {
 
 	@Provides
 	@Singleton
-	EventBus provideEventBus() {
-		return new EventBusImpl();
+	EventBus provideEventBus(@EventExecutor Executor eventExecutor) {
+		return new EventBusImpl(eventExecutor);
 	}
 }