Parse Config once when first used concurrently

cooldown.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -50,17 +51,16 @@ type Config struct {
 	defaultDuration    time.Duration
 	ecosystemDurations map[string]time.Duration
 	packageDurations   map[string]time.Duration
-	parsed             bool
+	parseOnce          sync.Once
 }
 
 // parse resolves all string durations into time.Duration values.
-// Called lazily on first use.
+// Called lazily on first use, once even when the first calls are concurrent.
 func (c *Config) parse() {
-	if c.parsed {
-		return
-	}
-	c.parsed = true
+	c.parseOnce.Do(c.parseDurations)
+}
 
+func (c *Config) parseDurations() {
 	c.defaultDuration, _ = ParseDuration(c.Default)
 
 	c.ecosystemDurations = make(map[string]time.Duration, len(c.Ecosystems))

cooldown_test.go

@@ -1,6 +1,7 @@
 package cooldown
 
 import (
+	"sync"
 	"testing"
 	"time"
 )
@@ -198,14 +199,14 @@ func TestConfigEvaluate(t *testing.T) {
 func TestConfigEnabled(t *testing.T) {
 	tests := []struct {
 		name string
-		cfg  Config
+		cfg  *Config
 		want bool
 	}{
-		{"empty config", Config{}, false},
-		{"default only", Config{Default: "3d"}, true},
-		{"ecosystem only", Config{Ecosystems: map[string]string{"npm": "7d"}}, true},
-		{"package only", Config{Packages: map[string]string{"pkg:npm/x": "1d"}}, true},
-		{"all zero", Config{Default: "0", Ecosystems: map[string]string{"npm": "0"}}, false},
+		{"empty config", &Config{}, false},
+		{"default only", &Config{Default: "3d"}, true},
+		{"ecosystem only", &Config{Ecosystems: map[string]string{"npm": "7d"}}, true},
+		{"package only", &Config{Packages: map[string]string{"pkg:npm/x": "1d"}}, true},
+		{"all zero", &Config{Default: "0", Ecosystems: map[string]string{"npm": "0"}}, false},
 	}
 
 	for _, tt := range tests {
@@ -217,3 +218,32 @@ func TestConfigEnabled(t *testing.T) {
 		})
 	}
 }
+
+func TestConfigConcurrentFirstUse(t *testing.T) {
+	for range 50 {
+		c := &Config{
+			Default:    "3d",
+			Ecosystems: map[string]string{"npm": "7d"},
+			Packages:   map[string]string{"pkg:npm/lodash": "1d"},
+		}
+		const n = 8
+		got := make([]time.Duration, n)
+		var start, wg sync.WaitGroup
+		start.Add(1)
+		for i := range n {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				start.Wait()
+				got[i] = c.For("npm", "pkg:npm/express")
+			}()
+		}
+		start.Done()
+		wg.Wait()
+		for i, d := range got {
+			if d != 7*24*time.Hour {
+				t.Fatalf("goroutine %d: For = %v, want 168h", i, d)
+			}
+		}
+	}
+}