fix: use a sync pool for strategy randomness, which offers slightly better perf under load

Author: sighphyre

internal/strategies/flexible_rollout.go

@@ -31,9 +31,9 @@ func (s flexibleRolloutStrategy) Name() string {
 func (s flexibleRolloutStrategy) resolveStickiness(st stickiness, ctx context.Context) string {
 	switch st {
 	case defaultStickiness:
-		return coalesce(ctx.UserId, ctx.SessionId, s.random.string())
+		return coalesce(ctx.UserId, ctx.SessionId, randomString())
 	case randomStickiness:
-		return s.random.string()
+		return randomString()
 	default:
 		return ctx.Field(string(st))
 	}

internal/strategies/helpers.go

@@ -89,3 +89,18 @@ func (r *rng) string() string {
 func newRng() *rng {
 	return &rng{random: rand.New(rand.NewPCG(uint64(time.Now().UnixNano()), uint64(os.Getpid())))}
 }
+
+var rngPool = sync.Pool{
+	New: func() any {
+		seed := time.Now().UnixNano() + int64(os.Getpid())
+		return rand.New(rand.NewSource(seed))
+	},
+}
+
+func randomString() string {
+	r := rngPool.Get().(*rand.Rand)
+	n := r.Intn(10000) + 1
+	rngPool.Put(r)
+
+	return strconv.Itoa(n)
+}