toAlertable

    fn toAlertable(s: Syscall) Io.Cancelable!AlertableSyscall {
        comptime assert(is_windows);
        const thread = s.thread orelse return .{ .thread = null };
        var prev = thread.status.load(.monotonic);
        while (true) prev = switch (prev.cancelation) {
            .none => unreachable,
            .parked => unreachable,
            .blocked_alertable => unreachable,
            .blocked_alertable_canceling => unreachable,
            .canceling => unreachable,
            .canceled => unreachable,

            .blocked => thread.status.cmpxchgWeak(prev, .{
                .cancelation = .blocked_alertable,
                .awaitable = prev.awaitable,
            }, .monotonic, .monotonic) orelse return .{ .thread = thread },

            .blocked_canceling => thread.status.cmpxchgWeak(prev, .{
                .cancelation = .canceled,
                .awaitable = prev.awaitable,
            }, .monotonic, .monotonic) orelse return error.Canceled,
        };
    }