WIP: Make EWMR allow zero times

Author: PeteGillinElastic

server/src/main/java/org/elasticsearch/common/metrics/ExponentiallyWeightedMovingRate.java

@@ -41,7 +41,8 @@ public class ExponentiallyWeightedMovingRate {
     private final double lambda;
     private final long startTime;
     private double rate;
-    long lastTime;
+    private long lastTime;
+    private boolean waitingForFirstIncrement;
 
     /**
      * Constructor.
@@ -57,14 +58,12 @@ public ExponentiallyWeightedMovingRate(double lambda, long startTime) {
         if (lambda < 0.0) {
             throw new IllegalArgumentException("lambda must be non-negative but was " + lambda);
         }
-        if (startTime <= 0.0) {
-            throw new IllegalArgumentException("startTime must be non-negative but was " + startTime);
-        }
         synchronized (this) {
             this.lambda = lambda;
             this.rate = Double.NaN; // should never be used
             this.startTime = startTime;
-            this.lastTime = 0; // after an increment, this must be positive, so a zero value indicates we're waiting for the first
+            this.lastTime = 0; // should never be used
+            this.waitingForFirstIncrement = true;
         }
     }
 
@@ -80,7 +79,7 @@ public ExponentiallyWeightedMovingRate(double lambda, long startTime) {
      */
     public double getRate(long time) {
         synchronized (this) {
-            if (lastTime == 0) { // indicates that no increment has happened yet
+            if (waitingForFirstIncrement) {
                 return 0.0;
             } else if (time <= lastTime) {
                 return rate;
@@ -130,12 +129,13 @@ public double calculateRateSince(long currentTime, double currentRate, long oldT
      */
     public void addIncrement(double increment, long time) {
         synchronized (this) {
-            if (lastTime == 0) { // indicates that this is the first increment
+            if (waitingForFirstIncrement) {
                 if (time <= startTime) {
                     time = startTime + 1;
                 }
                 // This is the formula for R(t_1) given in subsection 2.6 of the document referenced above:
                 rate = increment / expHelper(time - startTime);
+                waitingForFirstIncrement = false;
             } else {
                 if (time < lastTime) {
                     time = lastTime;

server/src/test/java/org/elasticsearch/common/metrics/ExponentiallyWeightedMovingRateTests.java

@@ -214,14 +214,6 @@ public void testEwmr_negativeLambdaThrowsOnConstruction() {
         assertThrows(IllegalArgumentException.class, () -> new ExponentiallyWeightedMovingRate(-1.0e-6, START_TIME_IN_MILLIS));
     }
 
-    public void testEwmr_zeroStartTimeInMillis() {
-        assertThrows(IllegalArgumentException.class, () -> new ExponentiallyWeightedMovingRate(LAMBDA, 0));
-    }
-
-    public void testEwmr_negativeStartTimeInMillis() {
-        assertThrows(IllegalArgumentException.class, () -> new ExponentiallyWeightedMovingRate(LAMBDA, -1));
-    }
-
     // N.B. This test is not guaranteed to fail even if the implementation is not thread-safe. The operations are fast enough that there is
     // a chance each thread will complete before the next one has started. We use a high thread count to try to get a decent change of
     // hitting a race condition if there is one. This should be run with e.g. -Dtests.iters=20 to test thoroughly.