Move toMillis(Duration) to Utils so that it can be reused. (#1114)

* Add toMillis() method to TimeUtils.

* Reuse toMillis() method in impl and exporters.

* Add a note about overflow and precision loss.

* Move toMillis() to Duration.

2 files changed, 4 insertions, 13 deletions

diff --git a/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java b/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java
index a35948a7..f114bea6 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/stats/IntervalBucket.java
@@ -18,7 +18,6 @@ package io.opencensus.implcore.stats;
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
-import static io.opencensus.implcore.stats.MutableViewData.toMillis;
 
 import com.google.common.collect.Maps;
 import io.opencensus.common.Duration;
@@ -82,7 +81,7 @@ final class IntervalBucket {
     checkArgument(
         elapsedTime.compareTo(ZERO) >= 0 && elapsedTime.compareTo(duration) < 0,
         "This bucket must be current.");
-    return ((double) toMillis(elapsedTime)) / toMillis(duration);
+    return ((double) Duration.toMillis(elapsedTime)) / Duration.toMillis(duration);
   }
 
   void clearStats() {
diff --git a/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java b/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
index 588b4897..f0938c06 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/stats/MutableViewData.java
@@ -66,9 +66,6 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 @SuppressWarnings("deprecation")
 abstract class MutableViewData {
 
-  private static final long MILLIS_PER_SECOND = 1000L;
-  private static final long NANOS_PER_MILLI = 1000 * 1000;
-
   @javax.annotation.Nullable @VisibleForTesting static final TagValue UNKNOWN_TAG_VALUE = null;
 
   @VisibleForTesting static final Timestamp ZERO_TIMESTAMP = Timestamp.create(0, 0);
@@ -149,11 +146,6 @@ abstract class MutableViewData {
     return tagValues;
   }
 
-  // Returns the milliseconds representation of a Duration.
-  static long toMillis(Duration duration) {
-    return duration.getSeconds() * MILLIS_PER_SECOND + duration.getNanos() / NANOS_PER_MILLI;
-  }
-
   /**
    * Create an empty {@link MutableAggregation} based on the given {@link Aggregation}.
    *
@@ -295,7 +287,7 @@ abstract class MutableViewData {
       super(view);
       Duration totalDuration = ((View.AggregationWindow.Interval) view.getWindow()).getDuration();
       this.totalDuration = totalDuration;
-      this.bucketDuration = Duration.fromMillis(toMillis(totalDuration) / N);
+      this.bucketDuration = Duration.fromMillis(Duration.toMillis(totalDuration) / N);
 
       // When initializing. add N empty buckets prior to the start timestamp of this
       // IntervalMutableViewData, so that the last bucket will be the current one in effect.
@@ -354,8 +346,8 @@ abstract class MutableViewData {
       checkArgument(
           now.compareTo(startOfLastBucket) >= 0,
           "Current time must be within or after the last bucket.");
-      long elapsedTimeMillis = toMillis(now.subtractTimestamp(startOfLastBucket));
-      long numOfPadBuckets = elapsedTimeMillis / toMillis(bucketDuration);
+      long elapsedTimeMillis = Duration.toMillis(now.subtractTimestamp(startOfLastBucket));
+      long numOfPadBuckets = elapsedTimeMillis / Duration.toMillis(bucketDuration);
 
       shiftBucketList(numOfPadBuckets, now);
     }