SntpClient periodically re-syncs the offset to NTP server

RELEASENOTES.md

@@ -54,6 +54,9 @@
     *   Remove `Renderer[]` parameter from `LoadControl.onTracksSelected()` as
         `DefaultLoadControl` implementation can retrieve the stream types from
         `ExoTrackSelection[]`.
+    *   Add a setter to `SntpClient` to set the max elapsed time since the last
+        update after which the client is re-initialized
+        ([#1794](https://github.com/androidx/media/pull/1794)).
     *   Deprecated `DefaultLoadControl.calculateTargetBufferBytes(Renderer[],
         ExoTrackSelection[])` and marked method as final to prevent overrides.
         The new

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/util/SntpClient.java

@@ -96,6 +96,12 @@ public interface InitializationCallback {
   @GuardedBy("valueLock")
   private static int timeoutMs = DEFAULT_TIMEOUT_MS;
 
+  @GuardedBy("valueLock")
+  private static long maxElapsedTimeUntilUpdateMs = C.TIME_UNSET;
+
+  @GuardedBy("valueLock")
+  private static long lastUpdateElapsedRealtime = C.TIME_UNSET;
+
   private SntpClient() {}
 
   /** Returns the NTP host address used to retrieve {@link #getElapsedRealtimeOffsetMs()}. */
@@ -148,6 +154,24 @@ public static void setTimeoutMs(int timeoutMs) {
     }
   }
 
+  /**
+   * Sets the maximum time to elapse until the client is re-initialized, in milliseconds.
+   *
+   * <p>The default is {@link C#TIME_UNSET} to never re-initialize.
+   */
+  public static void setMaxElapsedTimeUntilUpdateMs(long maxElapsedTimeUntilUpdateMs) {
+    synchronized (valueLock) {
+      SntpClient.maxElapsedTimeUntilUpdateMs = maxElapsedTimeUntilUpdateMs;
+    }
+  }
+
+  /** Returns the maximum time to elapse until the client is re-initialized, in milliseconds. */
+  public static long getMaxElapsedTimeUntilUpdateMs() {
+    synchronized (valueLock) {
+      return maxElapsedTimeUntilUpdateMs;
+    }
+  }
+
   /**
    * Returns whether the device time offset has already been loaded.
    *
@@ -156,6 +180,11 @@ public static void setTimeoutMs(int timeoutMs) {
    */
   public static boolean isInitialized() {
     synchronized (valueLock) {
+      if (lastUpdateElapsedRealtime != C.TIME_UNSET
+          && maxElapsedTimeUntilUpdateMs != C.TIME_UNSET) {
+        long deltaLastUpdate = SystemClock.elapsedRealtime() - lastUpdateElapsedRealtime;
+        isInitialized = isInitialized && deltaLastUpdate < maxElapsedTimeUntilUpdateMs;
+      }
       return isInitialized;
     }
   }
@@ -353,6 +382,7 @@ public void load() throws IOException {
         }
         long offsetMs = loadNtpTimeOffsetMs();
         synchronized (valueLock) {
+          lastUpdateElapsedRealtime = SystemClock.elapsedRealtime();
           elapsedRealtimeOffsetMs = offsetMs;
           isInitialized = true;
         }