Change grpcrand implementation to use Go top-level random functions f…

…or go1.21+

internal/grpcrand/grpcrand.go

@@ -1,3 +1,6 @@
+//go:build !go1.21
+// +build !go1.21
+
 /*
  *
  * Copyright 2018 gRPC authors.

internal/grpcrand/grpcrand_go1.21.go

@@ -0,0 +1,71 @@
+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package grpcrand implements math/rand functions in a concurrent-safe way
+// with a global random source, independent of math/rand's global source.
+package grpcrand
+
+import "math/rand"
+
+// This implementation will be used for Go version 1.21 or newer.
+// For older versions, the original implementation with mutex will be used.
+
+// Int implements rand.Int on the grpcrand global source.
+func Int() int {
+	return rand.Int()
+}
+
+// Int63n implements rand.Int63n on the grpcrand global source.
+func Int63n(n int64) int64 {
+	return rand.Int63n(n)
+}
+
+// Intn implements rand.Intn on the grpcrand global source.
+func Intn(n int) int {
+	return rand.Intn(n)
+}
+
+// Int31n implements rand.Int31n on the grpcrand global source.
+func Int31n(n int32) int32 {
+	return rand.Int31n(n)
+}
+
+// Float64 implements rand.Float64 on the grpcrand global source.
+func Float64() float64 {
+	return rand.Float64()
+}
+
+// Uint64 implements rand.Uint64 on the grpcrand global source.
+func Uint64() uint64 {
+	return rand.Uint64()
+}
+
+// Uint32 implements rand.Uint32 on the grpcrand global source.
+func Uint32() uint32 {
+	return rand.Uint32()
+}
+
+// ExpFloat64 implements rand.ExpFloat64 on the grpcrand global source.
+func ExpFloat64() float64 {
+	return rand.ExpFloat64()
+}
+
+// Shuffle implements rand.Shuffle on the grpcrand global source.
+var Shuffle = func(n int, f func(int, int)) {
+	rand.Shuffle(n, f)
+}