/
ListenerSet.java
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/
ListenerSet.java
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/*
* Copyright (C) 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.media3.common.util;
import android.os.Looper;
import android.os.Message;
import androidx.annotation.CheckResult;
import androidx.annotation.Nullable;
import androidx.media3.common.C;
import androidx.media3.common.FlagSet;
import java.util.ArrayDeque;
import java.util.concurrent.CopyOnWriteArraySet;
import org.checkerframework.checker.nullness.qual.NonNull;
/**
* A set of listeners.
*
* <p>Events are guaranteed to arrive in the order in which they happened even if a new event is
* triggered recursively from another listener.
*
* <p>Events are also guaranteed to be only sent to the listeners registered at the time the event
* was enqueued and haven't been removed since.
*
* @param <T> The listener type.
*/
@UnstableApi
public final class ListenerSet<T extends @NonNull Object> {
/**
* An event sent to a listener.
*
* @param <T> The listener type.
*/
public interface Event<T> {
/** Invokes the event notification on the given listener. */
void invoke(T listener);
}
/**
* An event sent to a listener when all other events sent during one {@link Looper} message queue
* iteration were handled by the listener.
*
* @param <T> The listener type.
*/
public interface IterationFinishedEvent<T> {
/**
* Invokes the iteration finished event.
*
* @param listener The listener to invoke the event on.
* @param eventFlags The combined event {@link FlagSet flags} of all events sent in this
* iteration.
*/
void invoke(T listener, FlagSet eventFlags);
}
private static final int MSG_ITERATION_FINISHED = 0;
private final Clock clock;
private final HandlerWrapper handler;
private final IterationFinishedEvent<T> iterationFinishedEvent;
private final CopyOnWriteArraySet<ListenerHolder<T>> listeners;
private final ArrayDeque<Runnable> flushingEvents;
private final ArrayDeque<Runnable> queuedEvents;
private boolean released;
/**
* Creates a new listener set.
*
* @param looper A {@link Looper} used to call listeners on. The same {@link Looper} must be used
* to call all other methods of this class.
* @param clock A {@link Clock}.
* @param iterationFinishedEvent An {@link IterationFinishedEvent} sent when all other events sent
* during one {@link Looper} message queue iteration were handled by the listeners.
*/
public ListenerSet(Looper looper, Clock clock, IterationFinishedEvent<T> iterationFinishedEvent) {
this(/* listeners= */ new CopyOnWriteArraySet<>(), looper, clock, iterationFinishedEvent);
}
private ListenerSet(
CopyOnWriteArraySet<ListenerHolder<T>> listeners,
Looper looper,
Clock clock,
IterationFinishedEvent<T> iterationFinishedEvent) {
this.clock = clock;
this.listeners = listeners;
this.iterationFinishedEvent = iterationFinishedEvent;
flushingEvents = new ArrayDeque<>();
queuedEvents = new ArrayDeque<>();
// It's safe to use "this" because we don't send a message before exiting the constructor.
@SuppressWarnings("nullness:methodref.receiver.bound")
HandlerWrapper handler = clock.createHandler(looper, this::handleMessage);
this.handler = handler;
}
/**
* Copies the listener set.
*
* @param looper The new {@link Looper} for the copied listener set.
* @param iterationFinishedEvent The new {@link IterationFinishedEvent} sent when all other events
* sent during one {@link Looper} message queue iteration were handled by the listeners.
* @return The copied listener set.
*/
@CheckResult
public ListenerSet<T> copy(Looper looper, IterationFinishedEvent<T> iterationFinishedEvent) {
return copy(looper, clock, iterationFinishedEvent);
}
/**
* Copies the listener set.
*
* @param looper The new {@link Looper} for the copied listener set.
* @param clock The new {@link Clock} for the copied listener set.
* @param iterationFinishedEvent The new {@link IterationFinishedEvent} sent when all other events
* sent during one {@link Looper} message queue iteration were handled by the listeners.
* @return The copied listener set.
*/
@CheckResult
public ListenerSet<T> copy(
Looper looper, Clock clock, IterationFinishedEvent<T> iterationFinishedEvent) {
return new ListenerSet<>(listeners, looper, clock, iterationFinishedEvent);
}
/**
* Adds a listener to the set.
*
* <p>If a listener is already present, it will not be added again.
*
* @param listener The listener to be added.
*/
public void add(T listener) {
if (released) {
return;
}
Assertions.checkNotNull(listener);
listeners.add(new ListenerHolder<>(listener));
}
/**
* Removes a listener from the set.
*
* <p>If the listener is not present, nothing happens.
*
* @param listener The listener to be removed.
*/
public void remove(T listener) {
for (ListenerHolder<T> listenerHolder : listeners) {
if (listenerHolder.listener.equals(listener)) {
listenerHolder.release(iterationFinishedEvent);
listeners.remove(listenerHolder);
}
}
}
/** Removes all listeners from the set. */
public void clear() {
listeners.clear();
}
/** Returns the number of added listeners. */
public int size() {
return listeners.size();
}
/**
* Adds an event that is sent to the listeners when {@link #flushEvents} is called.
*
* @param eventFlag An integer indicating the type of the event, or {@link C#INDEX_UNSET} to
* report this event without flag.
* @param event The event.
*/
public void queueEvent(int eventFlag, Event<T> event) {
CopyOnWriteArraySet<ListenerHolder<T>> listenerSnapshot = new CopyOnWriteArraySet<>(listeners);
queuedEvents.add(
() -> {
for (ListenerHolder<T> holder : listenerSnapshot) {
holder.invoke(eventFlag, event);
}
});
}
/** Notifies listeners of events previously enqueued with {@link #queueEvent(int, Event)}. */
public void flushEvents() {
if (queuedEvents.isEmpty()) {
return;
}
if (!handler.hasMessages(MSG_ITERATION_FINISHED)) {
handler.sendMessageAtFrontOfQueue(handler.obtainMessage(MSG_ITERATION_FINISHED));
}
boolean recursiveFlushInProgress = !flushingEvents.isEmpty();
flushingEvents.addAll(queuedEvents);
queuedEvents.clear();
if (recursiveFlushInProgress) {
// Recursive call to flush. Let the outer call handle the flush queue.
return;
}
while (!flushingEvents.isEmpty()) {
flushingEvents.peekFirst().run();
flushingEvents.removeFirst();
}
}
/**
* {@link #queueEvent(int, Event) Queues} a single event and immediately {@link #flushEvents()
* flushes} the event queue to notify all listeners.
*
* @param eventFlag An integer flag indicating the type of the event, or {@link C#INDEX_UNSET} to
* report this event without flag.
* @param event The event.
*/
public void sendEvent(int eventFlag, Event<T> event) {
queueEvent(eventFlag, event);
flushEvents();
}
/**
* Releases the set of listeners immediately.
*
* <p>This will ensure no events are sent to any listener after this method has been called.
*/
public void release() {
for (ListenerHolder<T> listenerHolder : listeners) {
listenerHolder.release(iterationFinishedEvent);
}
listeners.clear();
released = true;
}
private boolean handleMessage(Message message) {
for (ListenerHolder<T> holder : listeners) {
holder.iterationFinished(iterationFinishedEvent);
if (handler.hasMessages(MSG_ITERATION_FINISHED)) {
// The invocation above triggered new events (and thus scheduled a new message). We need
// to stop here because this new message will take care of informing every listener about
// the new update (including the ones already called here).
break;
}
}
return true;
}
private static final class ListenerHolder<T extends @NonNull Object> {
public final T listener;
private FlagSet.Builder flagsBuilder;
private boolean needsIterationFinishedEvent;
private boolean released;
public ListenerHolder(T listener) {
this.listener = listener;
this.flagsBuilder = new FlagSet.Builder();
}
public void release(IterationFinishedEvent<T> event) {
released = true;
if (needsIterationFinishedEvent) {
needsIterationFinishedEvent = false;
event.invoke(listener, flagsBuilder.build());
}
}
public void invoke(int eventFlag, Event<T> event) {
if (!released) {
if (eventFlag != C.INDEX_UNSET) {
flagsBuilder.add(eventFlag);
}
needsIterationFinishedEvent = true;
event.invoke(listener);
}
}
public void iterationFinished(IterationFinishedEvent<T> event) {
if (!released && needsIterationFinishedEvent) {
// Reset flags before invoking the listener to ensure we keep all new flags that are set by
// recursive events triggered from this callback.
FlagSet flagsToNotify = flagsBuilder.build();
flagsBuilder = new FlagSet.Builder();
needsIterationFinishedEvent = false;
event.invoke(listener, flagsToNotify);
}
}
@Override
public boolean equals(@Nullable Object other) {
if (this == other) {
return true;
}
if (other == null || getClass() != other.getClass()) {
return false;
}
return listener.equals(((ListenerHolder<?>) other).listener);
}
@Override
public int hashCode() {
return listener.hashCode();
}
}
}