Fix issue with stale createPeriod events in ConcatenatingMediaSource.

If a source is removed from the playlist, the player may still call createPeriod
for a period of the removed source as long as the new timeline hasn't been handled
by the player. These events are stale and can be ignored by using a dummy media
source. The stale media period will be released when the player handles the updated
timeline.

Issue:#4871

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=214787090

RELEASENOTES.md

@@ -138,6 +138,8 @@
 * Fix bugs reporting events for multi-period media sources
   ([#4492](https://github.com/google/ExoPlayer/issues/4492) and
   [#4634](https://github.com/google/ExoPlayer/issues/4634)).
+* Fix issue where removing looping media from a playlist throws an exception
+  ([#4871](https://github.com/google/ExoPlayer/issues/4871).
 * Fix issue where the preferred audio or text track would not be selected if
   mapped onto a secondary renderer of the corresponding type
   ([#4711](http://github.com/google/ExoPlayer/issues/4711)).

library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java

@@ -474,7 +474,12 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
   @Override
   public final MediaPeriod createPeriod(MediaPeriodId id, Allocator allocator) {
     Object mediaSourceHolderUid = getMediaSourceHolderUid(id.periodUid);
-    MediaSourceHolder holder = Assertions.checkNotNull(mediaSourceByUid.get(mediaSourceHolderUid));
+    MediaSourceHolder holder = mediaSourceByUid.get(mediaSourceHolderUid);
+    if (holder == null) {
+      // Stale event. The media source has already been removed.
+      holder = new MediaSourceHolder(new DummyMediaSource());
+      holder.hasStartedPreparing = true;
+    }
     DeferredMediaPeriod mediaPeriod = new DeferredMediaPeriod(holder.mediaSource, id, allocator);
     mediaSourceByMediaPeriod.put(mediaPeriod, holder);
     holder.activeMediaPeriods.add(mediaPeriod);
@@ -994,5 +999,37 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
       return DeferredTimeline.DUMMY_ID;
     }
   }
+
+  /** Dummy media source which does nothing and does not support creating periods. */
+  private static final class DummyMediaSource extends BaseMediaSource {
+
+    @Override
+    protected void prepareSourceInternal(
+        ExoPlayer player,
+        boolean isTopLevelSource,
+        @Nullable TransferListener mediaTransferListener) {
+      // Do nothing.
+    }
+
+    @Override
+    protected void releaseSourceInternal() {
+      // Do nothing.
+    }
+
+    @Override
+    public void maybeThrowSourceInfoRefreshError() throws IOException {
+      // Do nothing.
+    }
+
+    @Override
+    public MediaPeriod createPeriod(MediaPeriodId id, Allocator allocator) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void releasePeriod(MediaPeriod mediaPeriod) {
+      // Do nothing.
+    }
+  }
 }
 

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

@@ -2419,6 +2419,33 @@ public final class ExoPlayerTest {
     assertThat(renderer.hasReadStreamToEnd()).isTrue();
   }
 
+  @Test
+  public void removingLoopingLastPeriodFromPlaylistDoesNotThrow() throws Exception {
+    Timeline timeline =
+        new FakeTimeline(
+            new TimelineWindowDefinition(
+                /* isSeekable= */ true, /* isDynamic= */ true, /* durationUs= */ 100_000));
+    MediaSource mediaSource = new FakeMediaSource(timeline, /* manifest= */ null);
+    ConcatenatingMediaSource concatenatingMediaSource = new ConcatenatingMediaSource(mediaSource);
+    ActionSchedule actionSchedule =
+        new ActionSchedule.Builder("removingLoopingLastPeriodFromPlaylistDoesNotThrow")
+            .pause()
+            .waitForPlaybackState(Player.STATE_READY)
+            // Play almost to end to ensure the current period is fully buffered.
+            .playUntilPosition(/* windowIndex= */ 0, /* positionMs= */ 90)
+            // Enable repeat mode to trigger the creation of new media periods.
+            .setRepeatMode(Player.REPEAT_MODE_ALL)
+            // Remove the media source.
+            .executeRunnable(concatenatingMediaSource::clear)
+            .build();
+    new Builder()
+        .setMediaSource(concatenatingMediaSource)
+        .setActionSchedule(actionSchedule)
+        .build(context)
+        .start()
+        .blockUntilEnded(TIMEOUT_MS);
+  }
+
   // Internal methods.
 
   private static ActionSchedule.Builder addSurfaceSwitch(ActionSchedule.Builder builder) {