Optimize NewSafeID using atomic

messageID.go

@@ -1,6 +1,6 @@
 package slack
 
-import "sync"
+import "sync/atomic"
 
 // IDGenerator provides an interface for generating integer ID values.
 type IDGenerator interface {
@@ -11,20 +11,20 @@ type IDGenerator interface {
 // concurrent use by multiple goroutines.
 func NewSafeID(startID int) IDGenerator {
 	return &safeID{
-		nextID: startID,
-		mutex:  &sync.Mutex{},
+		nextID: int64(startID),
 	}
 }
 
 type safeID struct {
-	nextID int
-	mutex  *sync.Mutex
+	nextID int64
 }
 
+// make sure safeID implements the IDGenerator interface.
+var _ IDGenerator = (*safeID)(nil)
+
+// Next implements IDGenerator.Next.
 func (s *safeID) Next() int {
-	s.mutex.Lock()
-	defer s.mutex.Unlock()
-	id := s.nextID
-	s.nextID++
-	return id
+	id := atomic.AddInt64(&s.nextID, 1)
+
+	return int(id)
 }

messageID_test.go

@@ -0,0 +1,46 @@
+package slack
+
+import (
+	"testing"
+)
+
+func TestNewSafeID(t *testing.T) {
+	idgen := NewSafeID(1)
+	id1 := idgen.Next()
+	id2 := idgen.Next()
+	if id1 == id2 {
+		t.Fatalf("id1 and id2 are same: id1: %d, id2: %d", id1, id2)
+	}
+
+	idgen = NewSafeID(100)
+	id100 := idgen.Next()
+	id101 := idgen.Next()
+	if id2 == id100 {
+		t.Fatalf("except id2 and id100 not same: id2: %d, id101: %d", id2, id100)
+	}
+	if id100 == id101 {
+		t.Fatalf("id1 and id2 are same: id100: %d, id101: %d", id100, id101)
+	}
+}
+
+var id int
+
+func BenchmarkNewSafeID(b *testing.B) {
+	b.ReportAllocs()
+
+	idgen := NewSafeID(1)
+	for i := 0; i < b.N; i++ {
+		id = idgen.Next()
+	}
+}
+
+func BenchmarkNewSafeIDParallel(b *testing.B) {
+	b.ReportAllocs()
+
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			idgen := NewSafeID(1)
+			id = idgen.Next()
+		}
+	})
+}