futexWait

fn futexWait(userdata: ?*anyopaque, ptr: *const u32, expected: u32, timeout: Io.Timeout) Io.Cancelable!void {
    if (builtin.single_threaded) {
        assert(timeout != .none); // Deadlock.
        return;
    }
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    const t_io = io(t);
    const timeout_ns: ?u64 = ns: {
        const d = timeout.toDurationFromNow(t_io) orelse break :ns null;
        break :ns std.math.lossyCast(u64, d.raw.toNanoseconds());
    };
    return Thread.futexWait(ptr, expected, timeout_ns);
}