diff --git a/c/c.go b/c/c.go
index 9a20d8b1..2b8eada1 100644
--- a/c/c.go
+++ b/c/c.go
@@ -28,6 +28,7 @@ const (
 )
 
 type (
+	Void    = [0]byte
 	Char    = int8
 	Float   = float32
 	Double  = float64
diff --git a/x/io/_demo/asyncdemo/async.go b/x/io/_demo/asyncdemo/async.go
new file mode 100644
index 00000000..6d5362ae
--- /dev/null
+++ b/x/io/_demo/asyncdemo/async.go
@@ -0,0 +1,40 @@
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/goplus/llgo/x/io"
+)
+
+var GetUser = io.Async[any](func(string) any {
+	panic("todo: GetUser")
+})
+
+var GetScore = io.Async[float64](func() float64 {
+	panic("todo: GetScore")
+})
+
+var DoUpdate = io.Async[io.Void](func(op string) io.Void {
+	panic("todo: DoUpdate")
+})
+
+func main() {
+	user, err := GetUser("123").Await()
+	fmt.Println(user, err)
+
+	user, err = io.Race(GetUser("123"), GetUser("456"), GetUser("789")).Await()
+	fmt.Println(user, err)
+
+	user, score, _, err := io.Await3[any, float64, io.Void](GetUser("123"), GetScore(), DoUpdate("update sth."))
+	fmt.Println(user, score, err)
+
+	select {
+	case user := <-GetUser("123"):
+		fmt.Println("user:", user)
+	case score := <-GetScore():
+		fmt.Println("score:", score)
+	case <-io.Timeout(5 * time.Second):
+		fmt.Println("timeout")
+	}
+}
diff --git a/x/io/io.go b/x/io/io.go
new file mode 100644
index 00000000..8748673d
--- /dev/null
+++ b/x/io/io.go
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * 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 io
+
+import (
+	_ "unsafe"
+
+	"time"
+)
+
+const (
+	LLGoPackage = "decl"
+)
+
+type Void = [0]byte
+
+// -----------------------------------------------------------------------------
+
+type AsyncCall[OutT any] chan OutT
+
+// llgo:link AsyncCall.Await llgo.await
+func (AsyncCall[OutT]) Await(timeout ...time.Duration) (ret OutT, err error) {
+	return
+}
+
+//go:linkname Timeout llgo.timeout
+func Timeout(time.Duration) (ret AsyncCall[Void])
+
+// llgo:link Race llgo.race
+func Race[OutT any](acs ...AsyncCall[OutT]) (ret AsyncCall[OutT]) {
+	return
+}
+
+// llgo:link Await2 llgo.await
+func Await2[OutT1, OutT2 any](
+	ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2],
+	timeout ...time.Duration) (ret1 OutT1, ret2 OutT2, err error) {
+	return
+}
+
+// llgo:link Await3 llgo.await
+func Await3[OutT1, OutT2, OutT3 any](
+	ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2], ac3 AsyncCall[OutT3],
+	timeout ...time.Duration) (ret1 OutT1, ret2 OutT2, ret3 OutT3, err error) {
+	return
+}
+
+// -----------------------------------------------------------------------------
+
+type Promise[OutT any] func(...any) AsyncCall[OutT]
+
+// llgo:link Async llgo.async
+func Async[OutT any](fn any) (ret Promise[OutT]) {
+	return
+}
+
+// -----------------------------------------------------------------------------