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MutableLiveQueue.java
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MutableLiveQueue.java
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/*
* -\-\-
* Mobius
* --
* Copyright (c) 2017-2020 Spotify AB
* --
* 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 com.spotify.mobius.android;
import static androidx.lifecycle.Lifecycle.State.DESTROYED;
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.LifecycleOwner;
import androidx.lifecycle.Observer;
import androidx.lifecycle.OnLifecycleEvent;
import com.spotify.mobius.runners.WorkRunner;
import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
/**
* An internal implementation of {@link LiveQueue} that allows posting values.
*
* @param <T> The type of data to store and queue up
*/
final class MutableLiveQueue<T> implements LiveQueue<T> {
private class LifecycleObserverHelper implements LifecycleObserver {
@SuppressWarnings("unused")
@OnLifecycleEvent(Lifecycle.Event.ON_ANY)
void onAny(LifecycleOwner source, Lifecycle.Event event) {
onLifecycleChanged(event);
}
}
private final Object lock = new Object();
private final WorkRunner effectsWorkRunner;
private final BlockingQueue<T> pausedEffectsQueue;
@Nullable private Observer<T> liveObserver = null;
@Nullable private Observer<Iterable<T>> pausedObserver = null;
private boolean lifecycleOwnerIsPaused = true;
private boolean ignoreBackgroundEffects = false;
MutableLiveQueue(WorkRunner effectsWorkRunner, int capacity) {
this.effectsWorkRunner = effectsWorkRunner;
this.pausedEffectsQueue = new ArrayBlockingQueue<>(capacity);
}
@Override
public boolean hasActiveObserver() {
return liveObserver != null && !lifecycleOwnerIsPaused;
}
@Override
public boolean hasObserver() {
return liveObserver != null;
}
@Override
public void setObserver(@Nonnull LifecycleOwner owner, @Nonnull Observer<T> liveEffectsObserver) {
setObserver(owner, liveEffectsObserver, null);
}
@Override
public void setObserverIgnoringPausedEffects(
@Nonnull LifecycleOwner owner, @Nonnull Observer<T> liveEffectsObserver) {
synchronized (lock) {
setObserver(owner, liveEffectsObserver, null);
ignoreBackgroundEffects = true;
pausedEffectsQueue.clear();
}
}
@Override
public void setObserver(
@Nonnull LifecycleOwner lifecycleOwner,
@Nonnull Observer<T> liveObserver,
@Nullable Observer<Iterable<T>> pausedObserver) {
if (lifecycleOwner.getLifecycle().getCurrentState() == DESTROYED) {
return; // ignore
}
synchronized (lock) {
this.liveObserver = liveObserver;
this.pausedObserver = pausedObserver;
this.lifecycleOwnerIsPaused = true;
lifecycleOwner.getLifecycle().addObserver(new LifecycleObserverHelper());
ignoreBackgroundEffects = false;
}
}
@Override
public void clearObserver() {
synchronized (lock) {
liveObserver = null;
pausedObserver = null;
lifecycleOwnerIsPaused = true;
pausedEffectsQueue.clear();
}
}
/**
* This method will try to send the posted data to any observers
*
* @param data The data to send
*/
void post(@Nonnull final T data) {
synchronized (lock) {
if (lifecycleOwnerIsPaused) {
if (shouldQueuePausedEffects() && !pausedEffectsQueue.offer(data)) {
throw new IllegalStateException(
"Maximum effect queue size ("
+ pausedEffectsQueue.size()
+ ") exceeded when posting: "
+ data);
}
} else {
effectsWorkRunner.post(() -> sendToLiveObserver(data));
}
}
}
private boolean shouldQueuePausedEffects() {
return !ignoreBackgroundEffects;
}
private void onLifecycleChanged(Lifecycle.Event event) {
switch (event) {
case ON_RESUME:
synchronized (lock) {
lifecycleOwnerIsPaused = false;
sendQueuedEffects();
}
break;
case ON_PAUSE:
synchronized (lock) {
lifecycleOwnerIsPaused = true;
}
break;
case ON_DESTROY:
synchronized (lock) {
clearObserver();
}
break;
default:
// ignore other events
}
}
// errorprone recommends using ArrayDeque instead of LinkedList here, but ArrayDeque doesn't
// implement equals, so it's not very useful for testing, and performance isn't going to be an
// issue here
@SuppressWarnings("JdkObsolete")
private void sendQueuedEffects() {
final Queue<T> queueToSend = new LinkedList<>();
synchronized (lock) {
if (lifecycleOwnerIsPaused || pausedObserver == null || pausedEffectsQueue.isEmpty()) {
return;
}
pausedEffectsQueue.drainTo(queueToSend);
}
effectsWorkRunner.post(() -> sendToPausedObserver(queueToSend));
}
private void sendToLiveObserver(T data) {
synchronized (lock) {
if (liveObserver != null) {
liveObserver.onChanged(data);
}
}
}
private void sendToPausedObserver(Queue<T> queuedData) {
synchronized (lock) {
if (pausedObserver != null) {
pausedObserver.onChanged(queuedData);
}
}
}
}