From 4f2b596062090e12b6f68486593acd0f5a950e59 Mon Sep 17 00:00:00 2001
From: tonihei <tonihei@google.com>
Date: Wed, 20 Jun 2018 04:08:31 -0700
Subject: [PATCH] Allow to specify player looper at the time of ExoPlayer
 creation.

Currently, the looper of the thread the player is created on is used (or the
main looper if this thread doesn't have a looper). To allow more control over
the threading, this change lets users specificy the looper which must be used
to call player methods and which is used for event callbacks.

Issue:#4278

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=201331564
---
 RELEASENOTES.md                               |  2 +
 .../mediasession/MediaSessionConnector.java   | 22 ++---
 .../google/android/exoplayer2/ExoPlayer.java  | 23 ++---
 .../android/exoplayer2/ExoPlayerFactory.java  | 83 ++++++++++++++++++-
 .../android/exoplayer2/ExoPlayerImpl.java     | 27 ++++--
 .../android/exoplayer2/SimpleExoPlayer.java   | 54 +++++++++---
 .../source/ConcatenatingMediaSource.java      | 51 ++++--------
 .../google/android/exoplayer2/util/Util.java  | 14 +++-
 .../testutil/ExoPlayerTestRunner.java         |  4 +-
 .../testutil/MediaSourceTestRunner.java       |  5 ++
 .../exoplayer2/testutil/StubExoPlayer.java    |  5 ++
 11 files changed, 210 insertions(+), 80 deletions(-)

diff --git a/RELEASENOTES.md b/RELEASENOTES.md
index 3ae194c223c..87adaa88401 100644
--- a/RELEASENOTES.md
+++ b/RELEASENOTES.md
@@ -33,6 +33,8 @@
   ([#4385](https://github.com/google/ExoPlayer/issues/4385)).
 * Expose all internal ID3 data stored in MP4 udta boxes, and switch from using
   CommentFrame to InternalFrame for frames with gapless metadata in MP4.
+* Allow setting the `Looper`, which is used to access the player, in
+  `ExoPlayerFactory` ([#4278](https://github.com/google/ExoPlayer/issues/4278)).
 
 ### 2.8.2 ###
 
diff --git a/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java b/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java
index 4bafaa43260..e8758cd05b1 100644
--- a/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java
+++ b/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java
@@ -19,7 +19,6 @@
 import android.net.Uri;
 import android.os.Bundle;
 import android.os.Handler;
-import android.os.Looper;
 import android.os.ResultReceiver;
 import android.os.SystemClock;
 import android.support.annotation.NonNull;
@@ -39,6 +38,7 @@
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.util.ErrorMessageProvider;
 import com.google.android.exoplayer2.util.RepeatModeUtil;
+import com.google.android.exoplayer2.util.Util;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
@@ -323,7 +323,6 @@ public interface CustomActionProvider {
   public final MediaSessionCompat mediaSession;
 
   private final MediaControllerCompat mediaController;
-  private final Handler handler;
   private final boolean doMaintainMetadata;
   private final ExoPlayerEventListener exoPlayerEventListener;
   private final MediaSessionCallback mediaSessionCallback;
@@ -341,10 +340,9 @@ public interface CustomActionProvider {
   private RatingCallback ratingCallback;
 
   /**
-   * Creates an instance. Must be called on the same thread that is used to construct the player
-   * instances passed to {@link #setPlayer(Player, PlaybackPreparer, CustomActionProvider...)}.
-   * <p>
-   * Equivalent to {@code MediaSessionConnector(mediaSession, new DefaultPlaybackController())}.
+   * Creates an instance.
+   *
+   * <p>Equivalent to {@code MediaSessionConnector(mediaSession, new DefaultPlaybackController())}.
    *
    * @param mediaSession The {@link MediaSessionCompat} to connect to.
    */
@@ -353,8 +351,7 @@ public MediaSessionConnector(MediaSessionCompat mediaSession) {
   }
 
   /**
-   * Creates an instance. Must be called on the same thread that is used to construct the player
-   * instances passed to {@link #setPlayer(Player, PlaybackPreparer, CustomActionProvider...)}.
+   * Creates an instance.
    *
    * <p>Equivalent to {@code MediaSessionConnector(mediaSession, playbackController, true, null)}.
    *
@@ -367,8 +364,7 @@ public MediaSessionConnector(
   }
 
   /**
-   * Creates an instance. Must be called on the same thread that is used to construct the player
-   * instances passed to {@link #setPlayer(Player, PlaybackPreparer, CustomActionProvider...)}.
+   * Creates an instance.
    *
    * @param mediaSession The {@link MediaSessionCompat} to connect to.
    * @param playbackController A {@link PlaybackController} for handling playback actions, or {@code
@@ -388,8 +384,6 @@ public MediaSessionConnector(
     this.playbackController = playbackController != null ? playbackController
         : new DefaultPlaybackController();
     this.metadataExtrasPrefix = metadataExtrasPrefix != null ? metadataExtrasPrefix : "";
-    this.handler = new Handler(Looper.myLooper() != null ? Looper.myLooper()
-        : Looper.getMainLooper());
     this.doMaintainMetadata = doMaintainMetadata;
     mediaSession.setFlags(BASE_MEDIA_SESSION_FLAGS);
     mediaController = mediaSession.getController();
@@ -401,7 +395,8 @@ public MediaSessionConnector(
   }
 
   /**
-   * Sets the player to be connected to the media session.
+   * Sets the player to be connected to the media session. Must be called on the same thread that is
+   * used to access the player.
    *
    * <p>The order in which any {@link CustomActionProvider}s are passed determines the order of the
    * actions published with the playback state of the session.
@@ -428,6 +423,7 @@ public void setPlayer(
     this.customActionProviders = (player != null && customActionProviders != null)
         ? customActionProviders : new CustomActionProvider[0];
     if (player != null) {
+      Handler handler = new Handler(Util.getLooper());
       mediaSession.setCallback(mediaSessionCallback, handler);
       player.addListener(exoPlayerEventListener);
     }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java
index b97790d5fb2..ce43772d8db 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java
@@ -89,12 +89,13 @@
  * model">
  *
  * <ul>
- *   <li>ExoPlayer instances must be accessed from a single application thread. This must be the
- *       thread the player is created on if that thread has a {@link Looper}, or the application's
- *       main thread otherwise.
- *   <li>Registered listeners are called on the thread the player is created on if that thread has a
- *       {@link Looper}, or the application's main thread otherwise. Note that this means registered
- *       listeners are called on the same thread which must be used to access the player.
+ *   <li>ExoPlayer instances must be accessed from the thread associated with {@link
+ *       #getApplicationLooper()}. This Looper can be specified when creating the player, or this is
+ *       the Looper of the thread the player is created on, or the Looper of the application's main
+ *       thread if the player is created on a thread without Looper.
+ *   <li>Registered listeners are called on the thread thread associated with {@link
+ *       #getApplicationLooper()}. Note that this means registered listeners are called on the same
+ *       thread which must be used to access the player.
  *   <li>An internal playback thread is responsible for playback. Injected player components such as
  *       Renderers, MediaSources, TrackSelectors and LoadControls are called by the player on this
  *       thread.
@@ -178,12 +179,14 @@ public ExoPlayerMessage(PlayerMessage.Target target, int messageType, Object mes
   @Deprecated
   @RepeatMode int REPEAT_MODE_ALL = Player.REPEAT_MODE_ALL;
 
+  /** Returns the {@link Looper} associated with the playback thread. */
+  Looper getPlaybackLooper();
+
   /**
-   * Gets the {@link Looper} associated with the playback thread.
-   *
-   * @return The {@link Looper} associated with the playback thread.
+   * Returns the {@link Looper} associated with the application thread that's used to access the
+   * player and on which player events are received.
    */
-  Looper getPlaybackLooper();
+  Looper getApplicationLooper();
 
   /**
    * Prepares the player to play the provided {@link MediaSource}. Equivalent to
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java
index 8095ed9c640..e8bd8b34f6d 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java
@@ -16,12 +16,14 @@
 package com.google.android.exoplayer2;
 
 import android.content.Context;
+import android.os.Looper;
 import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.analytics.AnalyticsCollector;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.drm.FrameworkMediaCrypto;
 import com.google.android.exoplayer2.trackselection.TrackSelector;
 import com.google.android.exoplayer2.util.Clock;
+import com.google.android.exoplayer2.util.Util;
 
 /**
  * A factory for {@link ExoPlayer} instances.
@@ -156,7 +158,11 @@ public static SimpleExoPlayer newSimpleInstance(
   public static SimpleExoPlayer newSimpleInstance(RenderersFactory renderersFactory,
       TrackSelector trackSelector, LoadControl loadControl) {
     return new SimpleExoPlayer(
-        renderersFactory, trackSelector, loadControl, /* drmSessionManager= */ null);
+        renderersFactory,
+        trackSelector,
+        loadControl,
+        /* drmSessionManager= */ null,
+        Util.getLooper());
   }
 
   /**
@@ -173,7 +179,8 @@ public static SimpleExoPlayer newSimpleInstance(
       TrackSelector trackSelector,
       LoadControl loadControl,
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager) {
-    return new SimpleExoPlayer(renderersFactory, trackSelector, loadControl, drmSessionManager);
+    return new SimpleExoPlayer(
+        renderersFactory, trackSelector, loadControl, drmSessionManager, Util.getLooper());
   }
 
   /**
@@ -194,7 +201,62 @@ public static SimpleExoPlayer newSimpleInstance(
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
       AnalyticsCollector.Factory analyticsCollectorFactory) {
     return new SimpleExoPlayer(
-        renderersFactory, trackSelector, loadControl, drmSessionManager, analyticsCollectorFactory);
+        renderersFactory,
+        trackSelector,
+        loadControl,
+        drmSessionManager,
+        analyticsCollectorFactory,
+        Util.getLooper());
+  }
+
+  /**
+   * Creates a {@link SimpleExoPlayer} instance.
+   *
+   * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
+   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
+   * @param loadControl The {@link LoadControl} that will be used by the instance.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. May be null if the instance
+   *     will not be used for DRM protected playbacks.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
+   */
+  public static SimpleExoPlayer newSimpleInstance(
+      RenderersFactory renderersFactory,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
+      Looper looper) {
+    return new SimpleExoPlayer(
+        renderersFactory, trackSelector, loadControl, drmSessionManager, looper);
+  }
+
+  /**
+   * Creates a {@link SimpleExoPlayer} instance.
+   *
+   * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
+   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
+   * @param loadControl The {@link LoadControl} that will be used by the instance.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. May be null if the instance
+   *     will not be used for DRM protected playbacks.
+   * @param analyticsCollectorFactory A factory for creating the {@link AnalyticsCollector} that
+   *     will collect and forward all player events.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
+   */
+  public static SimpleExoPlayer newSimpleInstance(
+      RenderersFactory renderersFactory,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
+      AnalyticsCollector.Factory analyticsCollectorFactory,
+      Looper looper) {
+    return new SimpleExoPlayer(
+        renderersFactory,
+        trackSelector,
+        loadControl,
+        drmSessionManager,
+        analyticsCollectorFactory,
+        looper);
   }
 
   /**
@@ -216,7 +278,20 @@ public static ExoPlayer newInstance(Renderer[] renderers, TrackSelector trackSel
    */
   public static ExoPlayer newInstance(Renderer[] renderers, TrackSelector trackSelector,
       LoadControl loadControl) {
-    return new ExoPlayerImpl(renderers, trackSelector, loadControl, Clock.DEFAULT);
+    return newInstance(renderers, trackSelector, loadControl, Util.getLooper());
   }
 
+  /**
+   * Creates an {@link ExoPlayer} instance.
+   *
+   * @param renderers The {@link Renderer}s that will be used by the instance.
+   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
+   * @param loadControl The {@link LoadControl} that will be used by the instance.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
+   */
+  public static ExoPlayer newInstance(
+      Renderer[] renderers, TrackSelector trackSelector, LoadControl loadControl, Looper looper) {
+    return new ExoPlayerImpl(renderers, trackSelector, loadControl, Clock.DEFAULT, looper);
+  }
 }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java
index 390f8b59a59..e803fb30ee9 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java
@@ -81,10 +81,16 @@
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
    * @param loadControl The {@link LoadControl} that will be used by the instance.
    * @param clock The {@link Clock} that will be used by the instance.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    */
   @SuppressLint("HandlerLeak")
   public ExoPlayerImpl(
-      Renderer[] renderers, TrackSelector trackSelector, LoadControl loadControl, Clock clock) {
+      Renderer[] renderers,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      Clock clock,
+      Looper looper) {
     Log.i(TAG, "Init " + Integer.toHexString(System.identityHashCode(this)) + " ["
         + ExoPlayerLibraryInfo.VERSION_SLASHY + "] [" + Util.DEVICE_DEBUG_INFO + "]");
     Assertions.checkState(renderers.length > 0);
@@ -102,13 +108,13 @@ public ExoPlayerImpl(
     window = new Timeline.Window();
     period = new Timeline.Period();
     playbackParameters = PlaybackParameters.DEFAULT;
-    Looper eventLooper = Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper();
-    eventHandler = new Handler(eventLooper) {
-      @Override
-      public void handleMessage(Message msg) {
-        ExoPlayerImpl.this.handleEvent(msg);
-      }
-    };
+    eventHandler =
+        new Handler(looper) {
+          @Override
+          public void handleMessage(Message msg) {
+            ExoPlayerImpl.this.handleEvent(msg);
+          }
+        };
     playbackInfo =
         new PlaybackInfo(
             Timeline.EMPTY,
@@ -146,6 +152,11 @@ public Looper getPlaybackLooper() {
     return internalPlayer.getPlaybackLooper();
   }
 
+  @Override
+  public Looper getApplicationLooper() {
+    return eventHandler.getLooper();
+  }
+
   @Override
   public void addListener(Player.EventListener listener) {
     listeners.add(listener);
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java b/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java
index 7fa13338add..0fa72790794 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java
@@ -97,24 +97,41 @@ public interface VideoListener extends com.google.android.exoplayer2.video.Video
   private MediaSource mediaSource;
   private List<Cue> currentCues;
 
+  /**
+   * @deprecated Use {@link #SimpleExoPlayer(RenderersFactory, TrackSelector, LoadControl,
+   *     DrmSessionManager, Looper)}.
+   */
+  @Deprecated
+  protected SimpleExoPlayer(
+      RenderersFactory renderersFactory,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager) {
+    this(renderersFactory, trackSelector, loadControl, drmSessionManager, Util.getLooper());
+  }
+
   /**
    * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
    * @param loadControl The {@link LoadControl} that will be used by the instance.
    * @param drmSessionManager An optional {@link DrmSessionManager}. May be null if the instance
    *     will not be used for DRM protected playbacks.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    */
   protected SimpleExoPlayer(
       RenderersFactory renderersFactory,
       TrackSelector trackSelector,
       LoadControl loadControl,
-      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager) {
+      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
+      Looper looper) {
     this(
         renderersFactory,
         trackSelector,
         loadControl,
         drmSessionManager,
-        new AnalyticsCollector.Factory());
+        new AnalyticsCollector.Factory(),
+        looper);
   }
 
   /**
@@ -125,20 +142,24 @@ protected SimpleExoPlayer(
    *     will not be used for DRM protected playbacks.
    * @param analyticsCollectorFactory A factory for creating the {@link AnalyticsCollector} that
    *     will collect and forward all player events.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    */
   protected SimpleExoPlayer(
       RenderersFactory renderersFactory,
       TrackSelector trackSelector,
       LoadControl loadControl,
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
-      AnalyticsCollector.Factory analyticsCollectorFactory) {
+      AnalyticsCollector.Factory analyticsCollectorFactory,
+      Looper looper) {
     this(
         renderersFactory,
         trackSelector,
         loadControl,
         drmSessionManager,
         analyticsCollectorFactory,
-        Clock.DEFAULT);
+        Clock.DEFAULT,
+        looper);
   }
 
   /**
@@ -151,6 +172,8 @@ protected SimpleExoPlayer(
    *     will collect and forward all player events.
    * @param clock The {@link Clock} that will be used by the instance. Should always be {@link
    *     Clock#DEFAULT}, unless the player is being used from a test.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    */
   protected SimpleExoPlayer(
       RenderersFactory renderersFactory,
@@ -158,15 +181,15 @@ protected SimpleExoPlayer(
       LoadControl loadControl,
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
       AnalyticsCollector.Factory analyticsCollectorFactory,
-      Clock clock) {
+      Clock clock,
+      Looper looper) {
     componentListener = new ComponentListener();
     videoListeners = new CopyOnWriteArraySet<>();
     textOutputs = new CopyOnWriteArraySet<>();
     metadataOutputs = new CopyOnWriteArraySet<>();
     videoDebugListeners = new CopyOnWriteArraySet<>();
     audioDebugListeners = new CopyOnWriteArraySet<>();
-    Looper eventLooper = Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper();
-    eventHandler = new Handler(eventLooper);
+    eventHandler = new Handler(looper);
     renderers =
         renderersFactory.createRenderers(
             eventHandler,
@@ -184,7 +207,7 @@ protected SimpleExoPlayer(
     currentCues = Collections.emptyList();
 
     // Build the player and associated objects.
-    player = createExoPlayerImpl(renderers, trackSelector, loadControl, clock);
+    player = createExoPlayerImpl(renderers, trackSelector, loadControl, clock, looper);
     analyticsCollector = analyticsCollectorFactory.createAnalyticsCollector(player, clock);
     addListener(analyticsCollector);
     videoDebugListeners.add(analyticsCollector);
@@ -671,6 +694,11 @@ public Looper getPlaybackLooper() {
     return player.getPlaybackLooper();
   }
 
+  @Override
+  public Looper getApplicationLooper() {
+    return player.getApplicationLooper();
+  }
+
   @Override
   public void addListener(Player.EventListener listener) {
     player.addListener(listener);
@@ -954,11 +982,17 @@ public long getContentBufferedPosition() {
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
    * @param loadControl The {@link LoadControl} that will be used by the instance.
    * @param clock The {@link Clock} that will be used by this instance.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    * @return A new {@link ExoPlayer} instance.
    */
   protected ExoPlayer createExoPlayerImpl(
-      Renderer[] renderers, TrackSelector trackSelector, LoadControl loadControl, Clock clock) {
-    return new ExoPlayerImpl(renderers, trackSelector, loadControl, clock);
+      Renderer[] renderers,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      Clock clock,
+      Looper looper) {
+    return new ExoPlayerImpl(renderers, trackSelector, loadControl, clock, looper);
   }
 
   private void removeSurfaceCallbacks() {
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java b/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
index 52e44c3a4b0..680eea6a3ec 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
@@ -16,7 +16,6 @@
 package com.google.android.exoplayer2.source;
 
 import android.os.Handler;
-import android.os.Looper;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.C;
@@ -61,13 +60,14 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
   private final List<MediaSourceHolder> mediaSourceHolders;
   private final MediaSourceHolder query;
   private final Map<MediaPeriod, MediaSourceHolder> mediaSourceByMediaPeriod;
-  private final List<EventDispatcher> pendingOnCompletionActions;
+  private final List<Runnable> pendingOnCompletionActions;
   private final boolean isAtomic;
   private final boolean useLazyPreparation;
   private final Timeline.Window window;
   private final Timeline.Period period;
 
   private @Nullable ExoPlayer player;
+  private @Nullable Handler playerApplicationHandler;
   private boolean listenerNotificationScheduled;
   private ShuffleOrder shuffleOrder;
   private int windowCount;
@@ -351,11 +351,7 @@ public final synchronized void clear() {
   public final synchronized void clear(@Nullable Runnable actionOnCompletion) {
     mediaSourcesPublic.clear();
     if (player != null) {
-      player
-          .createMessage(this)
-          .setType(MSG_CLEAR)
-          .setPayload(actionOnCompletion != null ? new EventDispatcher(actionOnCompletion) : null)
-          .send();
+      player.createMessage(this).setType(MSG_CLEAR).setPayload(actionOnCompletion).send();
     } else if (actionOnCompletion != null) {
       actionOnCompletion.run();
     }
@@ -380,6 +376,7 @@ public final synchronized MediaSource getMediaSource(int index) {
   public final synchronized void prepareSourceInternal(ExoPlayer player, boolean isTopLevelSource) {
     super.prepareSourceInternal(player, isTopLevelSource);
     this.player = player;
+    playerApplicationHandler = new Handler(player.getApplicationLooper());
     if (mediaSourcesPublic.isEmpty()) {
       notifyListener();
     } else {
@@ -424,6 +421,7 @@ public final void releaseSourceInternal() {
     super.releaseSourceInternal();
     mediaSourceHolders.clear();
     player = null;
+    playerApplicationHandler = null;
     shuffleOrder = shuffleOrder.cloneAndClear();
     windowCount = 0;
     periodCount = 0;
@@ -462,6 +460,10 @@ protected int getWindowIndexForChildWindowIndex(
   @Override
   @SuppressWarnings("unchecked")
   public final void handleMessage(int messageType, Object message) throws ExoPlaybackException {
+    if (player == null) {
+      // Stale event.
+      return;
+    }
     switch (messageType) {
       case MSG_ADD:
         MessageData<MediaSourceHolder> addMessage = (MessageData<MediaSourceHolder>) message;
@@ -493,15 +495,16 @@ public final void handleMessage(int messageType, Object message) throws ExoPlayb
         break;
       case MSG_CLEAR:
         clearInternal();
-        scheduleListenerNotification((EventDispatcher) message);
+        scheduleListenerNotification((Runnable) message);
         break;
       case MSG_NOTIFY_LISTENER:
         notifyListener();
         break;
       case MSG_ON_COMPLETION:
-        List<EventDispatcher> actionsOnCompletion = ((List<EventDispatcher>) message);
+        List<Runnable> actionsOnCompletion = ((List<Runnable>) message);
+        Handler handler = Assertions.checkNotNull(playerApplicationHandler);
         for (int i = 0; i < actionsOnCompletion.size(); i++) {
-          actionsOnCompletion.get(i).dispatchEvent();
+          handler.post(actionsOnCompletion.get(i));
         }
         break;
       default:
@@ -509,7 +512,7 @@ public final void handleMessage(int messageType, Object message) throws ExoPlayb
     }
   }
 
-  private void scheduleListenerNotification(@Nullable EventDispatcher actionOnCompletion) {
+  private void scheduleListenerNotification(@Nullable Runnable actionOnCompletion) {
     if (!listenerNotificationScheduled) {
       Assertions.checkNotNull(player).createMessage(this).setType(MSG_NOTIFY_LISTENER).send();
       listenerNotificationScheduled = true;
@@ -521,9 +524,9 @@ private void scheduleListenerNotification(@Nullable EventDispatcher actionOnComp
 
   private void notifyListener() {
     listenerNotificationScheduled = false;
-    List<EventDispatcher> actionsOnCompletion =
+    List<Runnable> actionsOnCompletion =
         pendingOnCompletionActions.isEmpty()
-            ? Collections.<EventDispatcher>emptyList()
+            ? Collections.<Runnable>emptyList()
             : new ArrayList<>(pendingOnCompletionActions);
     pendingOnCompletionActions.clear();
     refreshSourceInfo(
@@ -698,34 +701,16 @@ public int compareTo(@NonNull MediaSourceHolder other) {
     }
   }
 
-  /** Can be used to dispatch a runnable on the thread the object was created on. */
-  private static final class EventDispatcher {
-
-    public final Handler eventHandler;
-    public final Runnable runnable;
-
-    public EventDispatcher(Runnable runnable) {
-      this.runnable = runnable;
-      this.eventHandler =
-          new Handler(Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper());
-    }
-
-    public void dispatchEvent() {
-      eventHandler.post(runnable);
-    }
-  }
-
   /** Message used to post actions from app thread to playback thread. */
   private static final class MessageData<T> {
 
     public final int index;
     public final T customData;
-    public final @Nullable EventDispatcher actionOnCompletion;
+    public final @Nullable Runnable actionOnCompletion;
 
     public MessageData(int index, T customData, @Nullable Runnable actionOnCompletion) {
       this.index = index;
-      this.actionOnCompletion =
-          actionOnCompletion != null ? new EventDispatcher(actionOnCompletion) : null;
+      this.actionOnCompletion = actionOnCompletion;
       this.customData = customData;
     }
   }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java b/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java
index 0e12964dfb3..7a38350563b 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java
@@ -252,11 +252,14 @@ public static <T> T[] nullSafeArrayCopy(T[] input, int length) {
    * assumption that the Handler won't be used to send messages until the callback is fully
    * initialized.
    *
+   * <p>If the current thread doesn't have a {@link Looper}, the application's main thread {@link
+   * Looper} is used.
+   *
    * @param callback A {@link Handler.Callback}. May be a partially initialized class.
    * @return A {@link Handler} with the specified callback on the current {@link Looper} thread.
    */
   public static Handler createHandler(Handler.@UnknownInitialization Callback callback) {
-    return createHandler(Looper.myLooper(), callback);
+    return createHandler(getLooper(), callback);
   }
 
   /**
@@ -275,6 +278,15 @@ public static Handler createHandler(
     return new Handler(looper, callback);
   }
 
+  /**
+   * Returns the {@link Looper} associated with the current thread, or the {@link Looper} of the
+   * application's main thread if the current thread doesn't have a {@link Looper}.
+   */
+  public static Looper getLooper() {
+    Looper myLooper = Looper.myLooper();
+    return myLooper != null ? myLooper : Looper.getMainLooper();
+  }
+
   /**
    * Instantiates a new single threaded executor whose thread has the specified name.
    *
diff --git a/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java b/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java
index cf7470b80a1..b47ab16db6d 100644
--- a/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java
+++ b/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java
@@ -18,6 +18,7 @@
 import static com.google.common.truth.Truth.assertThat;
 
 import android.os.HandlerThread;
+import android.os.Looper;
 import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.DefaultLoadControl;
 import com.google.android.exoplayer2.ExoPlaybackException;
@@ -663,7 +664,8 @@ public TestSimpleExoPlayer(
           loadControl,
           /* drmSessionManager= */ null,
           new AnalyticsCollector.Factory(),
-          clock);
+          clock,
+          Looper.myLooper());
     }
   }
 }
diff --git a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java
index ee3a3a2d323..5062b5c0052 100644
--- a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java
+++ b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java
@@ -442,6 +442,11 @@ public EventHandlingExoPlayer(Looper looper) {
       this.handler = new Handler(looper, this);
     }
 
+    @Override
+    public Looper getApplicationLooper() {
+      return handler.getLooper();
+    }
+
     @Override
     public PlayerMessage createMessage(PlayerMessage.Target target) {
       return new PlayerMessage(
diff --git a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java
index b8ad949f4ae..214c2b6a5e1 100644
--- a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java
+++ b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java
@@ -49,6 +49,11 @@ public Looper getPlaybackLooper() {
     throw new UnsupportedOperationException();
   }
 
+  @Override
+  public Looper getApplicationLooper() {
+    throw new UnsupportedOperationException();
+  }
+
   @Override
   public void addListener(Player.EventListener listener) {
     throw new UnsupportedOperationException();