Implement time measurement utility

Added a TimeMeasure interface as a utility class
to be able to measure running time of specific parts
of code. Usually, this will be used for benchmarking.

Implemented SamplerHistogramTimeMeasurement that uses
reservior sampling to calculate percentiles of large
amount of data.

Also updated maven pom.xml:
- update java version from 1.7 to 1.8 to be able to use java 8
- update guava to 27.0 to use Stats Percentiles
- update cassandra java plugin version to 3.6 to fix guava dependency problem

Change-Id: I168432ff2e6f5507fedc1678684dd96608703e5a
Issue-ID: MUSIC-148
Signed-off-by: Mohammad Salehe <salehe@cs.toronto.edu>

1 files changed, 52 insertions, 0 deletions

diff --git a/src/main/java/org/onap/music/util/TimeMeasure.java b/src/main/java/org/onap/music/util/TimeMeasure.java
new file mode 100644
index 00000000..cbb04ff6
--- /dev/null
+++ b/src/main/java/org/onap/music/util/TimeMeasure.java
@@ -0,0 +1,52 @@
+package org.onap.music.util;
+
+import org.apache.commons.lang3.tuple.Pair;
+
+import java.text.DecimalFormat;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.concurrent.ThreadLocalRandom;
+
+public interface TimeMeasure {
+    void enter(String context);
+
+    void exit();
+
+    /*
+        Return a map of measure contexts to a list of 101 percentiles [0,100]
+     */
+    Map<String, ArrayList<Double>> percentiles();
+
+    /*
+        Returns a map of measure contexts to <mean, sme>
+     */
+    Map<String, Pair<Double, Double>> stats();
+}
+
+class TimeMeasureExample
+{
+    public static void main(String[] args) {
+        TimeMeasure tm = new SamplerHistogramTimeMeasure();
+        double x = 0;
+
+        tm.enter("A");
+        for (int i = 0; i < 100000; i++) {
+            tm.enter("B");
+            tm.enter("C");
+            x += ThreadLocalRandom.current().nextDouble(100);
+            tm.exit();
+            tm.exit();
+        }
+        tm.enter("C");
+        tm.exit();
+        tm.exit();
+
+        System.out.println(x);
+        Map<String, ArrayList<Double>> e = tm.percentiles();
+        Map<String, Pair<Double, Double>> m = tm.stats();
+        DecimalFormat df = new DecimalFormat("000.000000");
+        e.forEach((k,v) -> System.out.println("" + k + "\t\t: " + Arrays.toString(v.stream().map(w -> "" + df.format(w)).toArray())));
+        m.forEach((k,v) -> System.out.println("" + k + "\t\t: " + df.format(v.getLeft()) + " (" + df.format(v.getRight()) + ")"));
+    }
+}