Add setPlaybackLooper ExoPlayer builder method

The method allows clients to specify a pre-existing thread
to use for playback. This can be used to run multiple ExoPlayer
instances on the same playback thread.

PiperOrigin-RevId: 488980749
(cherry picked from commit 79b809b5)

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java

@@ -24,6 +24,7 @@ import android.media.AudioDeviceInfo;
 import android.media.AudioTrack;
 import android.media.MediaCodec;
 import android.os.Looper;
+import android.os.Process;
 import android.view.Surface;
 import android.view.SurfaceHolder;
 import android.view.SurfaceView;
@@ -473,6 +474,7 @@ public interface ExoPlayer extends Player {
     /* package */ long detachSurfaceTimeoutMs;
     /* package */ boolean pauseAtEndOfMediaItems;
     /* package */ boolean usePlatformDiagnostics;
+    @Nullable /* package */ Looper playbackLooper;
     /* package */ boolean buildCalled;
 
     /**
@@ -515,6 +517,7 @@ public interface ExoPlayer extends Player {
      *   <li>{@code pauseAtEndOfMediaItems}: {@code false}
      *   <li>{@code usePlatformDiagnostics}: {@code true}
      *   <li>{@link Clock}: {@link Clock#DEFAULT}
+     *   <li>{@code playbackLooper}: {@code null} (create new thread)
      * </ul>
      *
      * @param context A {@link Context}.
@@ -1098,6 +1101,23 @@ public interface ExoPlayer extends Player {
     }
 
     /**
+     * Sets the {@link Looper} that will be used for playback.
+     *
+     * <p>The backing thread should run with priority {@link Process#THREAD_PRIORITY_AUDIO} and
+     * should handle messages within 10ms.
+     *
+     * @param playbackLooper A {@link looper}.
+     * @return This builder.
+     * @throws IllegalStateException If {@link #build()} has already been called.
+     */
+    @CanIgnoreReturnValue
+    public Builder setPlaybackLooper(Looper playbackLooper) {
+      checkState(!buildCalled);
+      this.playbackLooper = playbackLooper;
+      return this;
+    }
+
+    /**
      * Builds an {@link ExoPlayer} instance.
      *
      * @throws IllegalStateException If this method has already been called.

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java

@@ -334,7 +334,8 @@ import java.util.concurrent.TimeoutException;
               applicationLooper,
               clock,
               playbackInfoUpdateListener,
-              playerId);
+              playerId,
+              builder.playbackLooper);
 
       volume = 1;
       repeatMode = Player.REPEAT_MODE_OFF;

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImplInternal.java

@@ -181,7 +181,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
   private final LoadControl loadControl;
   private final BandwidthMeter bandwidthMeter;
   private final HandlerWrapper handler;
-  private final HandlerThread internalPlaybackThread;
+  @Nullable private final HandlerThread internalPlaybackThread;
   private final Looper playbackLooper;
   private final Timeline.Window window;
   private final Timeline.Period period;
@@ -236,7 +236,8 @@ import java.util.concurrent.atomic.AtomicBoolean;
       Looper applicationLooper,
       Clock clock,
       PlaybackInfoUpdateListener playbackInfoUpdateListener,
-      PlayerId playerId) {
+      PlayerId playerId,
+      Looper playbackLooper) {
     this.playbackInfoUpdateListener = playbackInfoUpdateListener;
     this.renderers = renderers;
     this.trackSelector = trackSelector;
@@ -277,12 +278,18 @@ import java.util.concurrent.atomic.AtomicBoolean;
     mediaSourceList =
         new MediaSourceList(/* listener= */ this, analyticsCollector, eventHandler, playerId);
 
-    // Note: The documentation for Process.THREAD_PRIORITY_AUDIO that states "Applications can
-    // not normally change to this priority" is incorrect.
-    internalPlaybackThread = new HandlerThread("ExoPlayer:Playback", Process.THREAD_PRIORITY_AUDIO);
-    internalPlaybackThread.start();
-    playbackLooper = internalPlaybackThread.getLooper();
-    handler = clock.createHandler(playbackLooper, this);
+    if (playbackLooper != null) {
+      internalPlaybackThread = null;
+      this.playbackLooper = playbackLooper;
+    } else {
+      // Note: The documentation for Process.THREAD_PRIORITY_AUDIO that states "Applications can
+      // not normally change to this priority" is incorrect.
+      internalPlaybackThread =
+          new HandlerThread("ExoPlayer:Playback", Process.THREAD_PRIORITY_AUDIO);
+      internalPlaybackThread.start();
+      this.playbackLooper = internalPlaybackThread.getLooper();
+    }
+    handler = clock.createHandler(this.playbackLooper, this);
   }
 
   public void experimentalSetForegroundModeTimeoutMs(long setForegroundModeTimeoutMs) {
@@ -385,7 +392,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 
   @Override
   public synchronized void sendMessage(PlayerMessage message) {
-    if (released || !internalPlaybackThread.isAlive()) {
+    if (released || !playbackLooper.getThread().isAlive()) {
       Log.w(TAG, "Ignoring messages sent after release.");
       message.markAsProcessed(/* isDelivered= */ false);
       return;
@@ -400,7 +407,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
    * @return Whether the operations succeeded. If false, the operation timed out.
    */
   public synchronized boolean setForegroundMode(boolean foregroundMode) {
-    if (released || !internalPlaybackThread.isAlive()) {
+    if (released || !playbackLooper.getThread().isAlive()) {
       return true;
     }
     if (foregroundMode) {
@@ -422,7 +429,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
    * @return Whether the release succeeded. If false, the release timed out.
    */
   public synchronized boolean release() {
-    if (released || !internalPlaybackThread.isAlive()) {
+    if (released || !playbackLooper.getThread().isAlive()) {
       return true;
     }
     handler.sendEmptyMessage(MSG_RELEASE);
@@ -1374,7 +1381,9 @@ import java.util.concurrent.atomic.AtomicBoolean;
         /* resetError= */ false);
     loadControl.onReleased();
     setState(Player.STATE_IDLE);
-    internalPlaybackThread.quit();
+    if (internalPlaybackThread != null) {
+      internalPlaybackThread.quit();
+    }
     synchronized (this) {
       released = true;
       notifyAll();