Introduce SystemClock#elapsedRealtimeNano.

Change-Id: I47e1b14d45c5321f959d46e1805f86aafd72f5d4

Author: Nick Pelly

api/current.txt

@@ -16342,6 +16342,7 @@ package android.os {
   public final class SystemClock {
     method public static long currentThreadTimeMillis();
     method public static long elapsedRealtime();
+    method public static long elapsedRealtimeNano();
     method public static boolean setCurrentTimeMillis(long);
     method public static void sleep(long);
     method public static long uptimeMillis();

core/java/android/os/SystemClock.java

@@ -46,15 +46,16 @@
  *     such as {@link Thread#sleep(long) Thread.sleep(millls)},
  *     {@link Object#wait(long) Object.wait(millis)}, and
  *     {@link System#nanoTime System.nanoTime()}.  This clock is guaranteed
- *     to be monotonic, and is the recommended basis for the general purpose
- *     interval timing of user interface events, performance measurements,
- *     and anything else that does not need to measure elapsed time during
- *     device sleep.  Most methods that accept a timestamp value expect the
- *     {@link #uptimeMillis} clock.
+ *     to be monotonic, and is suitable for interval timing when the
+ *     interval does not span device sleep.  Most methods that accept a
+ *     timestamp value currently expect the {@link #uptimeMillis} clock.
+ *
+ *     <li> <p> {@link #elapsedRealtime} and {@link #elapsedRealtimeNano}
+ *     return the time since the system was booted, and include deep sleep.
+ *     This clock is guaranteed to be monotonic, and continues to tick even
+ *     when the CPU is in power saving modes, so is the recommend basis
+ *     for general purpose interval timing.
  *
- *     <li> <p> {@link #elapsedRealtime} is counted in milliseconds since the
- *     system was booted, including deep sleep.  This clock should be used
- *     when measuring time intervals that may span periods of system sleep.
  * </ul>
  *
  * There are several mechanisms for controlling the timing of events:
@@ -150,7 +151,14 @@ public static void sleep(long ms)
      * @return elapsed milliseconds since boot.
      */
     native public static long elapsedRealtime();
-    
+
+    /**
+     * Returns nanoseconds since boot, including time spent in sleep.
+     *
+     * @return elapsed nanoseconds since boot.
+     */
+    public static native long elapsedRealtimeNano();
+
     /**
      * Returns milliseconds running in the current thread.
      * 

core/jni/android_os_SystemClock.cpp

@@ -111,6 +111,15 @@ static jlong android_os_SystemClock_currentTimeMicro(JNIEnv* env,
     return tv.tv_sec * 1000000LL + tv.tv_usec;
 }
 
+/*
+ * public static native long elapsedRealtimeNano();
+ */
+static jlong android_os_SystemClock_elapsedRealtimeNano(JNIEnv* env,
+        jobject clazz)
+{
+    return (jlong)elapsedRealtimeNano();
+}
+
 /*
  * JNI registration.
  */
@@ -128,6 +137,8 @@ static JNINativeMethod gMethods[] = {
             (void*) android_os_SystemClock_currentThreadTimeMicro },
     { "currentTimeMicro",             "()J",
             (void*) android_os_SystemClock_currentTimeMicro },
+    { "elapsedRealtimeNano",      "()J",
+            (void*) android_os_SystemClock_elapsedRealtimeNano },
 };
 int register_android_os_SystemClock(JNIEnv* env)
 {