Replace message delay with send at time in playback loop.

This removes the need to calculate the time needed to run the doSomeWork
method. Consequently, we can use both the real Clock/Handler and the
FakeClock without changing the way the playback loop works and without
violating the interfaces of Clock or Handler.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=180665647

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

@@ -117,6 +117,7 @@ import java.util.Collections;
   private final DefaultMediaClock mediaClock;
   private final PlaybackInfoUpdate playbackInfoUpdate;
   private final ArrayList<CustomMessageInfo> customMessageInfos;
+  private final Clock clock;
 
   @SuppressWarnings("unused")
   private SeekParameters seekParameters;
@@ -159,6 +160,7 @@ import java.util.Collections;
     this.shuffleModeEnabled = shuffleModeEnabled;
     this.eventHandler = eventHandler;
     this.player = player;
+    this.clock = clock;
 
     backBufferDurationUs = loadControl.getBackBufferDurationUs();
     retainBackBufferFromKeyframe = loadControl.retainBackBufferFromKeyframe();
@@ -541,7 +543,7 @@ import java.util.Collections;
   }
 
   private void doSomeWork() throws ExoPlaybackException, IOException {
-    long operationStartTimeMs = SystemClock.elapsedRealtime();
+    long operationStartTimeMs = clock.uptimeMillis();
     updatePeriods();
     if (playingPeriodHolder == null) {
       // We're still waiting for the first period to be prepared.
@@ -632,7 +634,7 @@ import java.util.Collections;
 
   private void scheduleNextWork(long thisOperationStartTimeMs, long intervalMs) {
     handler.removeMessages(MSG_DO_SOME_WORK);
-    handler.sendEmptyMessageDelayed(MSG_DO_SOME_WORK, intervalMs, thisOperationStartTimeMs);
+    handler.sendEmptyMessageAtTime(MSG_DO_SOME_WORK, thisOperationStartTimeMs + intervalMs);
   }
 
   private void seekToInternal(SeekPosition seekPosition) throws ExoPlaybackException {

library/core/src/main/java/com/google/android/exoplayer2/util/Clock.java

@@ -30,14 +30,13 @@ public interface Clock {
    */
   Clock DEFAULT = new SystemClock();
 
-  /**
-   * @see android.os.SystemClock#elapsedRealtime()
-   */
+  /** @see android.os.SystemClock#elapsedRealtime() */
   long elapsedRealtime();
 
-  /**
-   * @see android.os.SystemClock#sleep(long)
-   */
+  /** @see android.os.SystemClock#uptimeMillis() */
+  long uptimeMillis();
+
+  /** @see android.os.SystemClock#sleep(long) */
   void sleep(long sleepTimeMs);
 
   /**

library/core/src/main/java/com/google/android/exoplayer2/util/HandlerWrapper.java

@@ -43,18 +43,8 @@ public interface HandlerWrapper {
   /** @see Handler#sendEmptyMessage(int). */
   boolean sendEmptyMessage(int what);
 
-  /**
-   * Variant of {@code Handler#sendEmptyMessageDelayed(int, long)} which also takes a reference time
-   * measured by {@code android.os.SystemClock#elapsedRealtime()} to which the delay is added.
-   *
-   * @param what The message identifier.
-   * @param delayMs The delay in milliseconds to send the message. This delay is added to the {@code
-   *     referenceTimeMs}.
-   * @param referenceTimeMs The time which the delay is added to. Always measured with {@code
-   *     android.os.SystemClock#elapsedRealtime()}.
-   * @return Whether the message was successfully enqueued on the Handler thread.
-   */
-  boolean sendEmptyMessageDelayed(int what, long delayMs, long referenceTimeMs);
+  /** @see Handler#sendEmptyMessageAtTime(int, long). */
+  boolean sendEmptyMessageAtTime(int what, long uptimeMs);
 
   /** @see Handler#removeMessages(int). */
   void removeMessages(int what);

library/core/src/main/java/com/google/android/exoplayer2/util/SystemClock.java

@@ -31,6 +31,11 @@ import android.support.annotation.Nullable;
   }
 
   @Override
+  public long uptimeMillis() {
+    return android.os.SystemClock.uptimeMillis();
+  }
+
+  @Override
   public void sleep(long sleepTimeMs) {
     android.os.SystemClock.sleep(sleepTimeMs);
   }

library/core/src/main/java/com/google/android/exoplayer2/util/SystemHandlerWrapper.java

@@ -17,7 +17,6 @@ package com.google.android.exoplayer2.util;
 
 import android.os.Looper;
 import android.os.Message;
-import android.os.SystemClock;
 
 /** The standard implementation of {@link HandlerWrapper}. */
 /* package */ final class SystemHandlerWrapper implements HandlerWrapper {
@@ -59,14 +58,8 @@ import android.os.SystemClock;
   }
 
   @Override
-  public boolean sendEmptyMessageDelayed(int what, long delayMs, long referenceTimeMs) {
-    long targetMessageTime = referenceTimeMs + delayMs;
-    long remainingDelayMs = targetMessageTime - SystemClock.elapsedRealtime();
-    if (remainingDelayMs <= 0) {
-      return handler.sendEmptyMessage(what);
-    } else {
-      return handler.sendEmptyMessageDelayed(what, remainingDelayMs);
-    }
+  public boolean sendEmptyMessageAtTime(int what, long uptimeMs) {
+    return handler.sendEmptyMessageAtTime(what, uptimeMs);
   }
 
   @Override

testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeClock.java

@@ -68,6 +68,11 @@ public class FakeClock implements Clock {
   }
 
   @Override
+  public long uptimeMillis() {
+    return elapsedRealtime();
+  }
+
+  @Override
   public synchronized void sleep(long sleepTimeMs) {
     if (sleepTimeMs <= 0) {
       return;
@@ -90,15 +95,23 @@ public class FakeClock implements Clock {
   }
 
   /** Adds a handler post to list of pending messages. */
-  protected synchronized void addDelayedHandlerMessage(
-      HandlerWrapper handler, Runnable runnable, long delayMs) {
-    handlerMessages.add(new HandlerMessageData(currentTimeMs + delayMs, handler, runnable));
+  protected synchronized boolean addHandlerMessageAtTime(
+      HandlerWrapper handler, Runnable runnable, long timeMs) {
+    if (timeMs <= currentTimeMs) {
+      return handler.post(runnable);
+    }
+    handlerMessages.add(new HandlerMessageData(timeMs, handler, runnable));
+    return true;
   }
 
   /** Adds an empty handler message to list of pending messages. */
-  protected synchronized void addDelayedHandlerMessage(
-      HandlerWrapper handler, int message, long delayMs) {
-    handlerMessages.add(new HandlerMessageData(currentTimeMs + delayMs, handler, message));
+  protected synchronized boolean addHandlerMessageAtTime(
+      HandlerWrapper handler, int message, long timeMs) {
+    if (timeMs <= currentTimeMs) {
+      return handler.sendEmptyMessage(message);
+    }
+    handlerMessages.add(new HandlerMessageData(timeMs, handler, message));
+    return true;
   }
 
   /** Message data saved to send messages or execute runnables at a later time on a Handler. */
@@ -177,14 +190,8 @@ public class FakeClock implements Clock {
     }
 
     @Override
-    public boolean sendEmptyMessageDelayed(int what, long delayMs, long referenceTimeMs) {
-      // Ignore referenceTimeMs measured by SystemClock and just send with requested delay.
-      if (delayMs <= 0) {
-        return handler.sendEmptyMessage(what);
-      } else {
-        addDelayedHandlerMessage(this, what, delayMs);
-        return true;
-      }
+    public boolean sendEmptyMessageAtTime(int what, long uptimeMs) {
+      return addHandlerMessageAtTime(this, what, uptimeMs);
     }
 
     @Override
@@ -204,12 +211,7 @@ public class FakeClock implements Clock {
 
     @Override
     public boolean postDelayed(Runnable runnable, long delayMs) {
-      if (delayMs <= 0) {
-        return handler.post(runnable);
-      } else {
-        addDelayedHandlerMessage(this, runnable, delayMs);
-        return true;
-      }
+      return addHandlerMessageAtTime(this, runnable, uptimeMillis() + delayMs);
     }
   }
 }