Improve FakeClock and AutoAdvancingFakeClock

Issue: #4904
PiperOrigin-RevId: 337047518

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

@@ -20,16 +20,28 @@
 
 /**
  * {@link FakeClock} extension which automatically advances time whenever an empty message is
- * enqueued at a future time. The clock time is advanced to the time of the message. Only the first
- * Handler sending messages at a future time will be allowed to advance time to ensure there is only
- * one "time master". This should usually be the Handler of the internal playback loop.
+ * enqueued at a future time.
+ *
+ * <p>The clock time is advanced to the time of enqueued empty messages. Only the first Handler
+ * sending messages at a future time will be allowed to advance time to ensure there is only one
+ * primary time source. This should usually be the Handler of the internal playback loop.
  */
 public final class AutoAdvancingFakeClock extends FakeClock {
 
   private @MonotonicNonNull HandlerWrapper autoAdvancingHandler;
 
+  /** Creates the auto-advancing clock with an initial time of 0. */
   public AutoAdvancingFakeClock() {
-    super(/* initialTimeMs= */ 0);
+    this(/* initialTimeMs= */ 0);
+  }
+
+  /**
+   * Creates the auto-advancing clock.
+   *
+   * @param initialTimeMs The initial time of the clock in milliseconds.
+   */
+  public AutoAdvancingFakeClock(long initialTimeMs) {
+    super(initialTimeMs);
   }
 
   @Override

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

@@ -18,14 +18,24 @@
 import android.os.Handler.Callback;
 import android.os.Looper;
 import android.os.Message;
+import android.os.SystemClock;
 import androidx.annotation.GuardedBy;
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.util.Clock;
 import com.google.android.exoplayer2.util.HandlerWrapper;
 import java.util.ArrayList;
 import java.util.List;
 
-/** Fake {@link Clock} implementation independent of {@link android.os.SystemClock}. */
+/**
+ * Fake {@link Clock} implementation that allows to {@link #advanceTime(long) advance the time}
+ * manually to trigger pending timed messages.
+ *
+ * <p>All timed messages sent by a {@link #createHandler(Looper, Callback) Handler} created from
+ * this clock are governed by the clock's time.
+ *
+ * <p>The clock also sets the time of the {@link SystemClock} to match the {@link #elapsedRealtime()
+ * clock's time}.
+ */
 public class FakeClock implements Clock {
 
   private final List<Long> wakeUpTimes;
@@ -57,6 +67,7 @@ public FakeClock(long bootTimeMs, long initialTimeMs) {
     this.timeSinceBootMs = initialTimeMs;
     this.wakeUpTimes = new ArrayList<>();
     this.handlerMessages = new ArrayList<>();
+    SystemClock.setCurrentTimeMillis(initialTimeMs);
   }
 
   /**
@@ -66,6 +77,7 @@ public FakeClock(long bootTimeMs, long initialTimeMs) {
    */
   public synchronized void advanceTime(long timeDiffMs) {
     timeSinceBootMs += timeDiffMs;
+    SystemClock.setCurrentTimeMillis(timeSinceBootMs);
     for (Long wakeUpTime : wakeUpTimes) {
       if (wakeUpTime <= timeSinceBootMs) {
         notifyAll();