fix(random): avoid concurrent rand.Seed causing panic (#345)

random/random.go

@@ -10,7 +10,7 @@ import (
 	"io"
 	"math"
 	"math/rand"
-	"os"
+	"sync"
 	"time"
 	"unsafe"
 
@@ -27,7 +27,14 @@ const (
 	AllChars        = Numeral + LowwerLetters + UpperLetters + SymbolChars
 )
 
-var rn = rand.NewSource(time.Now().UnixNano())
+// var rn = rand.NewSource(time.Now().UnixNano())
+
+// 每个 goroutine 独立的 rand.Rand，避免并发问题
+var randPool = sync.Pool{
+	New: func() any {
+		return rand.New(rand.NewSource(time.Now().UnixNano()))
+	},
+}
 
 func init() {
 	rand.Seed(time.Now().UnixNano())
@@ -286,10 +293,9 @@ func nearestPowerOfTwo(cap int) int {
 
 // random generate a random string based on given string range.
 func random(s string, length int) string {
-	// 确保随机数生成器的种子是动态的
-	pid := os.Getpid()
-	timestamp := time.Now().UnixNano()
-	rand.Seed(int64(pid) + timestamp)
+	// 从 pool 中获取 rand.Rand（替代全局 rand）
+	rn := randPool.Get().(*rand.Rand)
+	defer randPool.Put(rn)
 
 	// 仿照strings.Builder
 	// 创建一个长度为 length 的字节切片

random/random_test.go

@@ -4,6 +4,7 @@ import (
 	"reflect"
 	"regexp"
 	"strconv"
+	"sync"
 	"testing"
 
 	"github.com/duke-git/lancet/v2/internal"
@@ -376,3 +377,31 @@ func TestRandNumberOfLength(t *testing.T) {
 	assert := internal.NewAssert(t, "TestRandNumberOfLength")
 	assert.Equal(6, len(strconv.Itoa(randi)))
 }
+
+// TestRandStringConcurrent verifies RandString is safe under high concurrency.
+// Before the fix, this test may panic or trigger data races.
+// After the fix, it should always pass.
+func TestRandStringConcurrent(t *testing.T) {
+	const (
+		goroutines = 100
+		iterations = 1000
+		length     = 32
+	)
+
+	var wg sync.WaitGroup
+	wg.Add(goroutines)
+
+	for g := 0; g < goroutines; g++ {
+		go func() {
+			defer wg.Done()
+			for i := 0; i < iterations; i++ {
+				s := RandString(length)
+				if len(s) != length {
+					t.Fatalf("unexpected string length: got %d, want %d", len(s), length)
+				}
+			}
+		}()
+	}
+
+	wg.Wait()
+}