From b65e0e2406adafe0b08338d54b48e5a40d920ff0 Mon Sep 17 00:00:00 2001
From: Coda Hale <coda.hale@gmail.com>
Date: Thu, 16 Jul 2020 14:30:17 -0600
Subject: [PATCH] Use proper types for measurements.

---
 cmd/usl/usl.go      |  4 ++--
 cmd/usl/usl_test.go |  2 --
 measurement.go      | 33 ++++++++++++++++++---------------
 measurement_test.go |  5 +++--
 4 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/cmd/usl/usl.go b/cmd/usl/usl.go
index c430d97..ec47b3f 100644
--- a/cmd/usl/usl.go
+++ b/cmd/usl/usl.go
@@ -196,12 +196,12 @@ func parseCSV(filename string, nCol, rCol int, skipHeaders bool) ([]usl.Measurem
 }
 
 //nolint:goerr113 // not a package
-func parseLine(i, nCol, xCol int, line []string) (float64, float64, error) {
+func parseLine(i, nCol, xCol int, line []string) (uint64, float64, error) {
 	if len(line) != 2 {
 		return 0, 0, fmt.Errorf("invalid line at line %d", i+1)
 	}
 
-	n, err := strconv.ParseFloat(line[nCol-1], 64)
+	n, err := strconv.ParseUint(line[nCol-1], 10, 64)
 	if err != nil {
 		return 0, 0, fmt.Errorf("error at line %d, column %d: %w", i+1, nCol, err)
 	}
diff --git a/cmd/usl/usl_test.go b/cmd/usl/usl_test.go
index 67bc478..10c3543 100644
--- a/cmd/usl/usl_test.go
+++ b/cmd/usl/usl_test.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"fmt"
 	"io/ioutil"
 	"os"
 	"testing"
@@ -62,7 +61,6 @@ func TestMainRun(t *testing.T) {
 `,
 		string(stdout))
 
-	fmt.Println(string(stderr))
 	assert.Equal(t, "stderr",
 		`URL parameters: σ=0.02772985648395876, κ=0.00010434289088915312, λ=89.98778453648904
 	max throughput: 1883.7622524836281, max concurrency: 96
diff --git a/measurement.go b/measurement.go
index 8a05b83..4d010c3 100644
--- a/measurement.go
+++ b/measurement.go
@@ -1,13 +1,16 @@
 package usl
 
-import "fmt"
+import (
+	"fmt"
+	"time"
+)
 
 // Measurement is a simultaneous measurement of at least two of the parameters of Little's Law:
 // concurrency, throughput, and latency. The third parameter is inferred from the other two.
 type Measurement struct {
 	Concurrency float64 // The average number of concurrent events.
-	Throughput  float64 // The long-term average arrival rate of events.
-	Latency     float64 // The average duration of events.
+	Throughput  float64 // The long-term average arrival rate of events, in events/sec.
+	Latency     float64 // The average duration of events in seconds.
 }
 
 func (m *Measurement) String() string {
@@ -16,30 +19,30 @@ func (m *Measurement) String() string {
 
 // ConcurrencyAndLatency returns a measurement of a system's latency at a given level of
 // concurrency. The throughput of the system is derived via Little's Law.
-func ConcurrencyAndLatency(n, r float64) Measurement {
+func ConcurrencyAndLatency(n uint64, r time.Duration) Measurement {
 	return Measurement{
-		Concurrency: n,     // L
-		Throughput:  n / r, // λ=L/W
-		Latency:     r,     // W
+		Concurrency: float64(n),               // L
+		Throughput:  float64(n) / r.Seconds(), // λ=L/W
+		Latency:     r.Seconds(),              // W
 	}
 }
 
 // ConcurrencyAndThroughput returns a measurement of a system's throughput at a given level of
 // concurrency. The latency of the system is derived via Little's Law.
-func ConcurrencyAndThroughput(n, x float64) Measurement {
+func ConcurrencyAndThroughput(n uint64, x float64) Measurement {
 	return Measurement{
-		Concurrency: n,     // L
-		Throughput:  x,     // λ
-		Latency:     n / x, // W=L/λ
+		Concurrency: float64(n),     // L
+		Throughput:  x,              // λ
+		Latency:     float64(n) / x, // W=L/λ
 	}
 }
 
 // ThroughputAndLatency returns a measurement of a system's latency at a given level of throughput.
 // The concurrency of the system is derived via Little's Law.
-func ThroughputAndLatency(x, r float64) Measurement {
+func ThroughputAndLatency(x float64, r time.Duration) Measurement {
 	return Measurement{
-		Concurrency: x * r, // L=λW
-		Throughput:  x,     // λ
-		Latency:     r,     // W
+		Concurrency: x * r.Seconds(), // L=λW
+		Throughput:  x,               // λ
+		Latency:     r.Seconds(),     // W
 	}
 }
diff --git a/measurement_test.go b/measurement_test.go
index 6168c95..597281a 100644
--- a/measurement_test.go
+++ b/measurement_test.go
@@ -2,6 +2,7 @@ package usl
 
 import (
 	"testing"
+	"time"
 
 	"github.com/codahale/usl/internal/assert"
 )
@@ -13,7 +14,7 @@ func TestMeasurement_String(t *testing.T) {
 }
 
 func TestConcurrencyAndLatency(t *testing.T) {
-	m := ConcurrencyAndLatency(3, 0.6)
+	m := ConcurrencyAndLatency(3, 600*time.Millisecond)
 
 	assert.Equal(t, "Concurrency", 3.0, m.Concurrency, epsilon)
 	assert.Equal(t, "Latency", 0.6, m.Latency, epsilon)
@@ -29,7 +30,7 @@ func TestConcurrencyAndThroughput(t *testing.T) {
 }
 
 func TestThroughputAndLatency(t *testing.T) {
-	m := ThroughputAndLatency(5, 0.6)
+	m := ThroughputAndLatency(5, 600*time.Millisecond)
 
 	assert.Equal(t, "Concurrency", 3.0, m.Concurrency, epsilon)
 	assert.Equal(t, "Latency", 0.6, m.Latency, epsilon)