Merge pull request #1105 from DataDog/louiszawadzki/rumm-2687/report-…

…harmonic-mean-of-js-refresh-rate

RUMM-2687 Invert frame time to get js refresh rate

dd-sdk-android/apiSurface

@@ -389,7 +389,7 @@ interface com.datadog.android.rum.RumMonitor
 enum com.datadog.android.rum.RumPerformanceMetric
   - FLUTTER_BUILD_TIME
   - FLUTTER_RASTER_TIME
-  - JS_REFRESH_RATE
+  - JS_FRAME_TIME
 interface com.datadog.android.rum.RumResourceAttributesProvider
   fun onProvideAttributes(okhttp3.Request, okhttp3.Response?, Throwable?): Map<String, Any?>
 enum com.datadog.android.rum.RumResourceKind

dd-sdk-android/src/main/kotlin/com/datadog/android/rum/RumPerformanceMetric.kt

@@ -17,6 +17,6 @@ enum class RumPerformanceMetric {
     /** The amount of time Flutter spent rasterizing the view. */
     FLUTTER_RASTER_TIME,
 
-    /** The JavaScript refresh rate of a React Native view. */
-    JS_REFRESH_RATE
+    /** The JavaScript frame time of a React Native view in nanoseconds. */
+    JS_FRAME_TIME
 }

dd-sdk-android/src/main/kotlin/com/datadog/android/rum/internal/domain/scope/RumViewScope.kt

@@ -626,8 +626,8 @@ internal open class RumViewScope(
                     ?.let { it.toPerformanceMetric() },
                 flutterRasterTime = performanceMetrics[RumPerformanceMetric.FLUTTER_RASTER_TIME]
                     ?.let { it.toPerformanceMetric() },
-                jsRefreshRate = performanceMetrics[RumPerformanceMetric.JS_REFRESH_RATE]
-                    ?.let { it.toPerformanceMetric() }
+                jsRefreshRate = performanceMetrics[RumPerformanceMetric.JS_FRAME_TIME]
+                    ?.let { it.toInversePerformanceMetric() }
             ),
             usr = ViewEvent.Usr(
                 id = user.id,
@@ -918,3 +918,26 @@ private fun VitalInfo.toPerformanceMetric(): ViewEvent.FlutterBuildTime {
         average = meanValue
     )
 }
+
+@Suppress("CommentOverPrivateFunction")
+/**
+ * This function is used to inverse frame times metrics into frame rates.
+ *
+ * As we take the inverse, the min of the inverse is the inverse of the max and
+ * vice-versa.
+ * For instance, if the the min frame time is 20ms (50 fps) and the max is 500ms (2 fps),
+ * the max frame rate is 50 fps (1/minValue) and the min is 2 fps (1/maxValue).
+ *
+ * As the frame times are reported in nanoseconds, we need to add a multiplier.
+ */
+private fun VitalInfo.toInversePerformanceMetric(): ViewEvent.FlutterBuildTime {
+    return ViewEvent.FlutterBuildTime(
+        min = invertValue(maxValue) * TimeUnit.SECONDS.toNanos(1),
+        max = invertValue(minValue) * TimeUnit.SECONDS.toNanos(1),
+        average = invertValue(meanValue) * TimeUnit.SECONDS.toNanos(1)
+    )
+}
+
+private fun invertValue(value: Double): Double {
+    return if (value == 0.0) 0.0 else 1.0 / value
+}

dd-sdk-android/src/test/kotlin/com/datadog/android/rum/internal/domain/scope/RumViewScopeTest.kt

@@ -6096,12 +6096,13 @@ internal class RumViewScopeTest {
         forge: Forge
     ) {
         // GIVEN
-        val value = forge.aDouble()
+        val value = forge.aPositiveDouble(true)
+        val frameRate = TimeUnit.SECONDS.toNanos(1) / value
 
         // WHEN
         testedScope.handleEvent(
             RumRawEvent.UpdatePerformanceMetric(
-                metric = RumPerformanceMetric.JS_REFRESH_RATE,
+                metric = RumPerformanceMetric.JS_FRAME_TIME,
                 value = value
             ),
             mockWriter
@@ -6118,7 +6119,7 @@ internal class RumViewScopeTest {
                 .apply {
                     hasFlutterBuildTime(null)
                     hasFlutterRasterTime(null)
-                    hasJsRefreshRate(ViewEvent.FlutterBuildTime(value, value, value, null))
+                    hasJsRefreshRate(ViewEvent.FlutterBuildTime(frameRate, frameRate, frameRate, null))
                 }
         }
         verifyNoMoreInteractions(mockWriter)
@@ -6132,7 +6133,7 @@ internal class RumViewScopeTest {
         // GIVEN
         val flutterBuildTimes = DoubleArray(5) { forge.aDouble() }
         val flutterRasterTimes = DoubleArray(5) { forge.aDouble() }
-        val jsRefreshRates = DoubleArray(5) { forge.aDouble() }
+        val jsFrameTimes = DoubleArray(5) { forge.aPositiveDouble(true) }
 
         // WHEN
         for (i in 0..4) {
@@ -6152,8 +6153,8 @@ internal class RumViewScopeTest {
             )
             testedScope.handleEvent(
                 RumRawEvent.UpdatePerformanceMetric(
-                    metric = RumPerformanceMetric.JS_REFRESH_RATE,
-                    value = jsRefreshRates[i]
+                    metric = RumPerformanceMetric.JS_FRAME_TIME,
+                    value = jsFrameTimes[i]
                 ),
                 mockWriter
             )
@@ -6166,7 +6167,7 @@ internal class RumViewScopeTest {
         // THEN
         val flutterBuildTimeStats = Arrays.stream(flutterBuildTimes).summaryStatistics()
         val flutterRasterTimeStats = Arrays.stream(flutterRasterTimes).summaryStatistics()
-        val jsRefreshRateStats = Arrays.stream(jsRefreshRates).summaryStatistics()
+        val jsFrameTimeStats = Arrays.stream(jsFrameTimes).summaryStatistics()
         argumentCaptor<ViewEvent> {
             verify(mockWriter).write(capture())
             assertThat(lastValue)
@@ -6187,9 +6188,9 @@ internal class RumViewScopeTest {
                     )
                     hasJsRefreshRate(
                         ViewEvent.FlutterBuildTime(
-                            min = jsRefreshRateStats.min,
-                            max = jsRefreshRateStats.max,
-                            average = jsRefreshRateStats.average
+                            min = TimeUnit.SECONDS.toNanos(1) / jsFrameTimeStats.max,
+                            max = TimeUnit.SECONDS.toNanos(1) / jsFrameTimeStats.min,
+                            average = TimeUnit.SECONDS.toNanos(1) / jsFrameTimeStats.average
                         )
                     )
                 }