Prevent unnecessary consecutive playlist loads

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=170078933

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/playlist/HlsPlaylistTracker.java

@@ -363,9 +363,8 @@ public final class HlsPlaylistTracker implements Loader.Callback<ParsingLoadable
    *
    * @param url The url of the playlist.
    * @param newSnapshot The new snapshot.
-   * @return True if a refresh should be scheduled.
    */
-  private boolean onPlaylistUpdated(HlsUrl url, HlsMediaPlaylist newSnapshot) {
+  private void onPlaylistUpdated(HlsUrl url, HlsMediaPlaylist newSnapshot) {
     if (url == primaryHlsUrl) {
       if (primaryUrlSnapshot == null) {
         // This is the first primary url snapshot.
@@ -378,8 +377,6 @@ public final class HlsPlaylistTracker implements Loader.Callback<ParsingLoadable
     for (int i = 0; i < listenersSize; i++) {
       listeners.get(i).onPlaylistChanged();
     }
-    // If the primary playlist is not the final one, we should schedule a refresh.
-    return url == primaryHlsUrl && !newSnapshot.hasEndTag;
   }
 
   private void notifyPlaylistBlacklisting(HlsUrl url, long blacklistMs) {
@@ -469,8 +466,9 @@ public final class HlsPlaylistTracker implements Loader.Callback<ParsingLoadable
     private HlsMediaPlaylist playlistSnapshot;
     private long lastSnapshotLoadMs;
     private long lastSnapshotChangeMs;
+    private long earliestNextLoadTimeMs;
     private long blacklistUntilMs;
-    private boolean pendingRefresh;
+    private boolean loadPending;
     private IOException playlistError;
 
     public MediaPlaylistBundle(HlsUrl playlistUrl) {
@@ -504,8 +502,16 @@ public final class HlsPlaylistTracker implements Loader.Callback<ParsingLoadable
 
     public void loadPlaylist() {
       blacklistUntilMs = 0;
-      if (!pendingRefresh && !mediaPlaylistLoader.isLoading()) {
-        mediaPlaylistLoader.startLoading(mediaPlaylistLoadable, this, minRetryCount);
+      if (loadPending || mediaPlaylistLoader.isLoading()) {
+        // Load already pending or in progress. Do nothing.
+        return;
+      }
+      long currentTimeMs = SystemClock.elapsedRealtime();
+      if (currentTimeMs < earliestNextLoadTimeMs) {
+        loadPending = true;
+        playlistRefreshHandler.postDelayed(this, earliestNextLoadTimeMs - currentTimeMs);
+      } else {
+        loadPlaylistImmediately();
       }
     }
 
@@ -549,8 +555,7 @@ public final class HlsPlaylistTracker implements Loader.Callback<ParsingLoadable
       }
       boolean shouldRetry = true;
       if (ChunkedTrackBlacklistUtil.shouldBlacklist(error)) {
-        blacklistPlaylist();
-        shouldRetry = primaryHlsUrl == playlistUrl && !maybeSelectNewPrimaryUrl();
+        shouldRetry = blacklistPlaylist();
       }
       return shouldRetry ? Loader.RETRY : Loader.DONT_RETRY;
     }
@@ -559,48 +564,60 @@ public final class HlsPlaylistTracker implements Loader.Callback<ParsingLoadable
 
     @Override
     public void run() {
-      pendingRefresh = false;
-      loadPlaylist();
+      loadPending = false;
+      loadPlaylistImmediately();
     }
 
     // Internal methods.
 
+    private void loadPlaylistImmediately() {
+      mediaPlaylistLoader.startLoading(mediaPlaylistLoadable, this, minRetryCount);
+    }
+
     private void processLoadedPlaylist(HlsMediaPlaylist loadedPlaylist) {
       HlsMediaPlaylist oldPlaylist = playlistSnapshot;
       long currentTimeMs = SystemClock.elapsedRealtime();
       lastSnapshotLoadMs = currentTimeMs;
       playlistSnapshot = getLatestPlaylistSnapshot(oldPlaylist, loadedPlaylist);
-      long refreshDelayUs = C.TIME_UNSET;
       if (playlistSnapshot != oldPlaylist) {
         playlistError = null;
         lastSnapshotChangeMs = currentTimeMs;
-        if (onPlaylistUpdated(playlistUrl, playlistSnapshot)) {
-          refreshDelayUs = playlistSnapshot.targetDurationUs;
-        }
+        onPlaylistUpdated(playlistUrl, playlistSnapshot);
       } else if (!playlistSnapshot.hasEndTag) {
-        if (currentTimeMs - lastSnapshotChangeMs
+        if (loadedPlaylist.mediaSequence + loadedPlaylist.segments.size()
+            < playlistSnapshot.mediaSequence) {
+          // The media sequence jumped backwards. The server has probably reset.
+          playlistError = new PlaylistResetException(playlistUrl.url);
+        } else if (currentTimeMs - lastSnapshotChangeMs
             > C.usToMs(playlistSnapshot.targetDurationUs)
                 * PLAYLIST_STUCK_TARGET_DURATION_COEFFICIENT) {
-          // The playlist seems to be stuck, we blacklist it.
+          // The playlist seems to be stuck. Blacklist it.
           playlistError = new PlaylistStuckException(playlistUrl.url);
           blacklistPlaylist();
-        } else if (loadedPlaylist.mediaSequence + loadedPlaylist.segments.size()
-            < playlistSnapshot.mediaSequence) {
-          // The media sequence has jumped backwards. The server has likely reset.
-          playlistError = new PlaylistResetException(playlistUrl.url);
         }
-        refreshDelayUs = playlistSnapshot.targetDurationUs / 2;
       }
-      if (refreshDelayUs != C.TIME_UNSET) {
-        // See HLS spec v20, section 6.3.4 for more information on media playlist refreshing.
-        pendingRefresh = playlistRefreshHandler.postDelayed(this, C.usToMs(refreshDelayUs));
+      // Do not allow the playlist to load again within the target duration if we obtained a new
+      // snapshot, or half the target duration otherwise.
+      earliestNextLoadTimeMs = currentTimeMs + C.usToMs(playlistSnapshot != oldPlaylist
+          ? playlistSnapshot.targetDurationUs : (playlistSnapshot.targetDurationUs / 2));
+      // Schedule a load if this is the primary playlist and it doesn't have an end tag. Else the
+      // next load will be scheduled when refreshPlaylist is called, or when this playlist becomes
+      // the primary.
+      if (playlistUrl == primaryHlsUrl && !playlistSnapshot.hasEndTag) {
+        loadPlaylist();
       }
     }
 
-    private void blacklistPlaylist() {
+    /**
+     * Blacklists the playlist.
+     *
+     * @return Whether the playlist is the primary, despite being blacklisted.
+     */
+    private boolean blacklistPlaylist() {
       blacklistUntilMs = SystemClock.elapsedRealtime()
           + ChunkedTrackBlacklistUtil.DEFAULT_TRACK_BLACKLIST_MS;
       notifyPlaylistBlacklisting(playlistUrl, ChunkedTrackBlacklistUtil.DEFAULT_TRACK_BLACKLIST_MS);
+      return primaryHlsUrl == playlistUrl && !maybeSelectNewPrimaryUrl();
     }
 
   }