Remove initial seek counting in ExoPlayerImplInternal.

We can acknoledge seeks before preparation finished immediately now,
because ExoPlayerImpl won't leave the masking state until the first prepare
operation is processed.

As a side effect, it also cleans up the responsibility of the callbacks.
Prepares are always acknowledged with a SOURCE_INFO_REFRESHED, while seeks
are always acknowledged with a SEEK_ACK.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177144089

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

@@ -306,11 +306,19 @@ public final class ExoPlayerTest extends TestCase {
   public void testSeekProcessedCallback() throws Exception {
     Timeline timeline = new FakeTimeline(/* windowCount= */ 2);
     ActionSchedule actionSchedule = new ActionSchedule.Builder("testSeekProcessedCallback")
-        // Initial seek before timeline preparation finished.
-        .pause().seek(10).waitForPlaybackState(Player.STATE_READY)
-        // Re-seek to same position, start playback and wait until playback reaches second window.
-        .seek(10).play().waitForPositionDiscontinuity()
-        // Seek twice in concession, expecting the first seek to be replaced.
+        // Initial seek before timeline preparation started. Expect immediate seek processed while
+        // the player is still in STATE_IDLE.
+        .pause().seek(5)
+        // Wait until the media source starts preparing and issue more initial seeks. Expect only
+        // one seek processed after the source has been prepared.
+        .waitForPlaybackState(Player.STATE_BUFFERING).seek(2).seek(10)
+        // Wait until media source prepared and re-seek to same position. Expect a seek processed
+        // while still being in STATE_READY.
+        .waitForPlaybackState(Player.STATE_READY).seek(10)
+        // Start playback and wait until playback reaches second window.
+        .play().waitForPositionDiscontinuity()
+        // Seek twice in concession, expecting the first seek to be replaced (and thus except only
+        // on seek processed callback).
         .seek(5).seek(60).build();
     final List<Integer> playbackStatesWhenSeekProcessed = new ArrayList<>();
     Player.EventListener eventListener = new Player.DefaultEventListener() {
@@ -329,10 +337,11 @@ public final class ExoPlayerTest extends TestCase {
     new ExoPlayerTestRunner.Builder()
         .setTimeline(timeline).setEventListener(eventListener).setActionSchedule(actionSchedule)
         .build().start().blockUntilEnded(TIMEOUT_MS);
-    assertEquals(3, playbackStatesWhenSeekProcessed.size());
-    assertEquals(Player.STATE_BUFFERING, (int) playbackStatesWhenSeekProcessed.get(0));
-    assertEquals(Player.STATE_READY, (int) playbackStatesWhenSeekProcessed.get(1));
-    assertEquals(Player.STATE_BUFFERING, (int) playbackStatesWhenSeekProcessed.get(2));
+    assertEquals(4, playbackStatesWhenSeekProcessed.size());
+    assertEquals(Player.STATE_IDLE, (int) playbackStatesWhenSeekProcessed.get(0));
+    assertEquals(Player.STATE_BUFFERING, (int) playbackStatesWhenSeekProcessed.get(1));
+    assertEquals(Player.STATE_READY, (int) playbackStatesWhenSeekProcessed.get(2));
+    assertEquals(Player.STATE_BUFFERING, (int) playbackStatesWhenSeekProcessed.get(3));
   }
 
   public void testSeekDiscontinuity() throws Exception {
@@ -742,7 +751,7 @@ public final class ExoPlayerTest extends TestCase {
         .waitForPlaybackState(Player.STATE_IDLE)
         // If we were still using the first timeline, this would throw.
         .seek(/* windowIndex= */ 1, /* positionMs= */ 0)
-        .prepareSource(secondSource)
+        .prepareSource(secondSource, /* resetPosition= */ false, /* resetState= */ true)
         .build();
     ExoPlayerTestRunner testRunner = new ExoPlayerTestRunner.Builder()
         .setTimeline(timeline)

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

@@ -450,8 +450,7 @@ import java.util.concurrent.CopyOnWriteArraySet;
       }
       case ExoPlayerImplInternal.MSG_SOURCE_INFO_REFRESHED: {
         int prepareOrStopAcks = msg.arg1;
-        int seekAcks = msg.arg2;
-        handlePlaybackInfo((PlaybackInfo) msg.obj, prepareOrStopAcks, seekAcks, false,
+        handlePlaybackInfo((PlaybackInfo) msg.obj, prepareOrStopAcks, 0, false,
             /* ignored */ DISCONTINUITY_REASON_INTERNAL);
         break;
       }
@@ -510,13 +509,13 @@ import java.util.concurrent.CopyOnWriteArraySet;
       boolean timelineOrManifestChanged = this.playbackInfo.timeline != playbackInfo.timeline
           || this.playbackInfo.manifest != playbackInfo.manifest;
       this.playbackInfo = playbackInfo;
-      if (playbackInfo.timeline.isEmpty()) {
-        // Update the masking variables, which are used when the timeline is empty.
-        maskingPeriodIndex = 0;
-        maskingWindowIndex = 0;
-        maskingWindowPositionMs = 0;
-      }
       if (timelineOrManifestChanged || waitingForInitialTimeline) {
+        if (playbackInfo.timeline.isEmpty()) {
+          // Update the masking variables, which are used when the timeline becomes empty.
+          maskingPeriodIndex = 0;
+          maskingWindowIndex = 0;
+          maskingWindowPositionMs = 0;
+        }
         @Player.TimelineChangeReason int reason = waitingForInitialTimeline
             ? Player.TIMELINE_CHANGE_REASON_PREPARED : Player.TIMELINE_CHANGE_REASON_DYNAMIC;
         waitingForInitialTimeline = false;

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

@@ -125,8 +125,7 @@ import java.io.IOException;
   private long elapsedRealtimeUs;
 
   private int pendingPrepareCount;
-  private int pendingInitialSeekCount;
-  private SeekPosition pendingSeekPosition;
+  private SeekPosition pendingInitialSeekPosition;
   private long rendererPositionUs;
 
   private MediaPeriodHolder loadingPeriodHolder;
@@ -631,8 +630,9 @@ import java.io.IOException;
   private void seekToInternal(SeekPosition seekPosition) throws ExoPlaybackException {
     Timeline timeline = playbackInfo.timeline;
     if (timeline == null) {
-      pendingInitialSeekCount++;
-      pendingSeekPosition = seekPosition;
+      pendingInitialSeekPosition = seekPosition;
+      eventHandler.obtainMessage(MSG_SEEK_ACK, /* seekAdjusted = */ 0, 0,
+          playbackInfo.copyWithTimeline(Timeline.EMPTY, null)).sendToTarget();
       return;
     }
 
@@ -781,7 +781,7 @@ import java.io.IOException;
     }
     int prepareOrStopAcks = pendingPrepareCount + 1;
     pendingPrepareCount = 0;
-    notifySourceInfoRefresh(prepareOrStopAcks, 0, publicPlaybackInfo);
+    notifySourceInfoRefresh(prepareOrStopAcks, publicPlaybackInfo);
     loadControl.onStopped();
     setState(Player.STATE_IDLE);
   }
@@ -825,6 +825,7 @@ import java.io.IOException;
           ? 0
           : timeline.getWindow(timeline.getFirstWindowIndex(shuffleModeEnabled), window)
               .firstPeriodIndex;
+      pendingInitialSeekPosition = null;
       playbackInfo = playbackInfo.fromNewPosition(firstPeriodIndex, C.TIME_UNSET, C.TIME_UNSET);
     } else {
       // The new start position is the current playback position.
@@ -1009,15 +1010,13 @@ import java.io.IOException;
     if (oldTimeline == null) {
       int processedPrepareAcks = pendingPrepareCount;
       pendingPrepareCount = 0;
-      if (pendingInitialSeekCount > 0) {
-        Pair<Integer, Long> periodPosition = resolveSeekPosition(pendingSeekPosition);
-        int processedInitialSeekCount = pendingInitialSeekCount;
-        pendingInitialSeekCount = 0;
-        pendingSeekPosition = null;
+      if (pendingInitialSeekPosition != null) {
+        Pair<Integer, Long> periodPosition = resolveSeekPosition(pendingInitialSeekPosition);
+        pendingInitialSeekPosition = null;
         if (periodPosition == null) {
           // The seek position was valid for the timeline that it was performed into, but the
           // timeline has changed and a suitable seek position could not be resolved in the new one.
-          handleSourceInfoRefreshEndedPlayback(processedPrepareAcks, processedInitialSeekCount);
+          handleSourceInfoRefreshEndedPlayback(processedPrepareAcks);
         } else {
           int periodIndex = periodPosition.first;
           long positionUs = periodPosition.second;
@@ -1025,11 +1024,11 @@ import java.io.IOException;
               mediaPeriodInfoSequence.resolvePeriodPositionForAds(periodIndex, positionUs);
           playbackInfo = playbackInfo.fromNewPosition(periodId, periodId.isAd() ? 0 : positionUs,
               positionUs);
-          notifySourceInfoRefresh(processedPrepareAcks, processedInitialSeekCount);
+          notifySourceInfoRefresh(processedPrepareAcks);
         }
       } else if (playbackInfo.startPositionUs == C.TIME_UNSET) {
         if (timeline.isEmpty()) {
-          handleSourceInfoRefreshEndedPlayback(processedPrepareAcks, 0);
+          handleSourceInfoRefreshEndedPlayback(processedPrepareAcks);
         } else {
           Pair<Integer, Long> defaultPosition = getPeriodPosition(timeline,
               timeline.getFirstWindowIndex(shuffleModeEnabled), C.TIME_UNSET);
@@ -1039,10 +1038,10 @@ import java.io.IOException;
               startPositionUs);
           playbackInfo = playbackInfo.fromNewPosition(periodId,
               periodId.isAd() ? 0 : startPositionUs, startPositionUs);
-          notifySourceInfoRefresh(processedPrepareAcks, 0);
+          notifySourceInfoRefresh(processedPrepareAcks);
         }
       } else {
-        notifySourceInfoRefresh(processedPrepareAcks, 0);
+        notifySourceInfoRefresh(processedPrepareAcks);
       }
       return;
     }
@@ -1169,30 +1168,29 @@ import java.io.IOException;
   }
 
   private void handleSourceInfoRefreshEndedPlayback() {
-    handleSourceInfoRefreshEndedPlayback(0, 0);
+    handleSourceInfoRefreshEndedPlayback(0);
   }
 
-  private void handleSourceInfoRefreshEndedPlayback(int prepareAcks, int seekAcks) {
+  private void handleSourceInfoRefreshEndedPlayback(int prepareAcks) {
     setState(Player.STATE_ENDED);
     // Reset, but retain the source so that it can still be used should a seek occur.
     resetInternal(false, true);
     // Set the playback position to 0 for notifying the eventHandler (instead of C.TIME_UNSET).
-    notifySourceInfoRefresh(prepareAcks, seekAcks,
+    notifySourceInfoRefresh(prepareAcks,
         playbackInfo.fromNewPosition(playbackInfo.periodId.periodIndex, 0, C.TIME_UNSET));
   }
 
   private void notifySourceInfoRefresh() {
-    notifySourceInfoRefresh(0, 0);
+    notifySourceInfoRefresh(0);
   }
 
-  private void notifySourceInfoRefresh(int prepareOrStopAcks, int seekAcks) {
-    notifySourceInfoRefresh(prepareOrStopAcks, seekAcks, playbackInfo);
+  private void notifySourceInfoRefresh(int prepareOrStopAcks) {
+    notifySourceInfoRefresh(prepareOrStopAcks, playbackInfo);
   }
 
-  private void notifySourceInfoRefresh(int prepareOrStopAcks, int seekAcks,
-      PlaybackInfo playbackInfo) {
-    eventHandler.obtainMessage(MSG_SOURCE_INFO_REFRESHED, prepareOrStopAcks, seekAcks,
-        playbackInfo).sendToTarget();
+  private void notifySourceInfoRefresh(int prepareOrStopAcks, PlaybackInfo playbackInfo) {
+    eventHandler.obtainMessage(MSG_SOURCE_INFO_REFRESHED, prepareOrStopAcks, 0, playbackInfo)
+        .sendToTarget();
   }
 
   /**