--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgo/go/internal/syscall/unix/nonblocking_libc.go	Mon May 25 07:50:57 2020 +0900
@@ -0,0 +1,20 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build aix darwin solaris
+
+package unix
+
+import "syscall"
+
+//extern __go_fcntl_uintptr
+func fcntl(uintptr, uintptr, uintptr) (uintptr, uintptr)
+
+func IsNonblock(fd int) (nonblocking bool, err error) {
+	flag, e1 := fcntl(uintptr(fd), syscall.F_GETFL, 0)
+	if e1 != 0 {
+		return false, syscall.Errno(e1)
+	}
+	return flag&syscall.O_NONBLOCK != 0, nil
+}