improving the concurrency performance of random value calculation

client/cache/random_expired_cache.go

@@ -17,6 +17,7 @@ package cache
 import (
 	"context"
 	"math/rand"
+	"sync/atomic"
 	"time"
 )
 
@@ -44,12 +45,25 @@ func NewRandomExpireCache(adapter Cache, opts ...RandomExpireCacheOption) Cache
 		fn(&rec)
 	}
 	if rec.Offset == nil {
-		rec.Offset = defaultExpiredFunc
+		rec.Offset = defaultExpiredFunc()
 	}
 	return &rec
 }
 
-// defaultExpiredFunc genreate random time offset expired
-func defaultExpiredFunc() time.Duration {
-	return time.Duration(rand.Intn(5)+3) * time.Second
+// defaultExpiredFunc return a func that used to generate random time offset (range: [3s,8s)) expired
+func defaultExpiredFunc() func() time.Duration {
+	const size = 5
+	var randTimes [size]time.Duration
+	for i := range randTimes {
+		randTimes[i] = time.Duration(i + 3)
+	}
+	// shuffle values
+	for i := range randTimes {
+		n := rand.Intn(size)
+		randTimes[i], randTimes[n] = randTimes[n], randTimes[i]
+	}
+	var i uint64
+	return func() time.Duration {
+		return randTimes[atomic.AddUint64(&i, 1)%size]
+	}
 }

client/cache/random_expired_cache_test.go

@@ -29,7 +29,7 @@ func TestRandomExpireCache(t *testing.T) {
 
 	// cache := NewRandomExpireCache(bm)
 	cache := NewRandomExpireCache(bm, func(opt *RandomExpireCache) {
-		opt.offset = defaultExpiredFunc
+		opt.Offset = defaultExpiredFunc()
 	})
 
 	timeoutDuration := 3 * time.Second