Post AudioFocusManager.onAudioFocusChange events to eventHandler.

PiperOrigin-RevId: 276452333

RELEASENOTES.md

@@ -85,6 +85,8 @@
     `VideoDecoderOutputBufferRenderer`, instead of `VideoDecoderSurfaceView`.
 * Add automatic audio becoming noisy handling to `SimpleExoPlayer`,
   available through `SimpleExoPlayer.setHandleAudioBecomingNoisy`.
+* Post `AudioFocusManager.onAudioFocusChange` events to eventHandler, avoiding
+  multithreaded access to the player or audio focus manager.
 * Add `Timeline.Window.isLive` to indicate that a window is a live stream
   ([#2668](https://github.com/google/ExoPlayer/issues/2668) and
   [#5973](https://github.com/google/ExoPlayer/issues/5973)).

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

@@ -18,6 +18,7 @@ package com.google.android.exoplayer2;
 import android.content.Context;
 import android.media.AudioFocusRequest;
 import android.media.AudioManager;
+import android.os.Handler;
 import androidx.annotation.IntDef;
 import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
@@ -114,13 +115,14 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
    * Constructs an AudioFocusManager to automatically handle audio focus for a player.
    *
    * @param context The current context.
+   * @param eventHandler A {@link Handler} to for the thread on which the player is used.
    * @param playerControl A {@link PlayerControl} to handle commands from this instance.
    */
-  public AudioFocusManager(Context context, PlayerControl playerControl) {
+  public AudioFocusManager(Context context, Handler eventHandler, PlayerControl playerControl) {
     this.audioManager =
         (AudioManager) context.getApplicationContext().getSystemService(Context.AUDIO_SERVICE);
     this.playerControl = playerControl;
-    this.focusListener = new AudioFocusListener();
+    this.focusListener = new AudioFocusListener(eventHandler);
     this.audioFocusState = AUDIO_FOCUS_STATE_NO_FOCUS;
   }
 
@@ -380,11 +382,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     }
   }
 
-  // Internal audio focus listener.
-
-  private class AudioFocusListener implements AudioManager.OnAudioFocusChangeListener {
-    @Override
-    public void onAudioFocusChange(int focusChange) {
+  private void handleAudioFocusChange(int focusChange) {
     // Convert the platform focus change to internal state.
     switch (focusChange) {
       case AudioManager.AUDIOFOCUS_LOSS:
@@ -440,5 +438,19 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       playerControl.setVolumeMultiplier(volumeMultiplier);
     }
   }
+
+  // Internal audio focus listener.
+
+  private class AudioFocusListener implements AudioManager.OnAudioFocusChangeListener {
+    private final Handler eventHandler;
+
+    public AudioFocusListener(Handler eventHandler) {
+      this.eventHandler = eventHandler;
+    }
+
+    @Override
+    public void onAudioFocusChange(int focusChange) {
+      eventHandler.post(() -> handleAudioFocusChange(focusChange));
+    }
   }
 }

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

@@ -456,7 +456,7 @@ public class SimpleExoPlayer extends BasePlayer
     }
     audioBecomingNoisyManager =
         new AudioBecomingNoisyManager(context, eventHandler, componentListener);
-    audioFocusManager = new AudioFocusManager(context, componentListener);
+    audioFocusManager = new AudioFocusManager(context, eventHandler, componentListener);
     wakeLockManager = new WakeLockManager(context);
   }
 

library/core/src/test/java/com/google/android/exoplayer2/AudioFocusManagerTest.java

@@ -25,6 +25,8 @@ import static org.robolectric.annotation.Config.TARGET_SDK;
 import android.content.Context;
 import android.media.AudioFocusRequest;
 import android.media.AudioManager;
+import android.os.Handler;
+import android.os.Looper;
 import androidx.test.core.app.ApplicationProvider;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import com.google.android.exoplayer2.audio.AudioAttributes;
@@ -54,7 +56,10 @@ public class AudioFocusManagerTest {
 
     testPlayerControl = new TestPlayerControl();
     audioFocusManager =
-        new AudioFocusManager(ApplicationProvider.getApplicationContext(), testPlayerControl);
+        new AudioFocusManager(
+            ApplicationProvider.getApplicationContext(),
+            new Handler(Looper.myLooper()),
+            testPlayerControl);
   }
 
   @Test