sw.fmu.RUnlock()

	af, err := f.apply(so)
	if err != nil {
		return syscall.InvalidHandle, err
	}
	s, so.Err = windows.WSASocket(family, sotype, proto, protinfo, group, flags)
	if err = af.apply(so); err != nil {
		if so.Err == nil {
			syscall.Closesocket(s)
		}
		return syscall.InvalidHandle, err
	}

	sw.smu.Lock()
	defer sw.smu.Unlock()
	if so.Err != nil {

// responsiveness on machines with high CPU utilization.
func createWindowsJobObject(pc uint32) (windows.Handle, error) {
	job, err := windows.CreateJobObject(nil, nil)
	if err != nil {
		return windows.InvalidHandle, fmt.Errorf("windows.CreateJobObject failed: %w", err)
	}
	limitInfo := windows.JOBOBJECT_BASIC_LIMIT_INFORMATION{
		LimitFlags:    windows.JOB_OBJECT_LIMIT_PRIORITY_CLASS,
		PriorityClass: pc,
	}

	s, err := wsaSocketFunc(int32(family), int32(sotype), int32(proto),
		nil, 0, windows.WSA_FLAG_OVERLAPPED|windows.WSA_FLAG_NO_HANDLE_INHERIT)
	if err != nil {
		return syscall.InvalidHandle, os.NewSyscallError("socket", err)
	}
	return s, nil

	}

	return os.NewFile(uintptr(fd), path), nil
}

func lockFile(fd syscall.Handle, flags uint32) error {
	// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx
	if fd == syscall.InvalidHandle {
		return nil
	}

	err := lockFileEx(fd, flags, 1, 0, &syscall.Overlapped{})
	if err == nil || err == errLockViolation {
		return nil
	}