deregister

    fn deregister(cond: *Condition, io: Io) void {
        var prev_state = cond.state.load(.monotonic);
        while (true) {
            const new_signals = @min(prev_state.signals, prev_state.waiters - 1);
            prev_state = cond.state.cmpxchgWeak(prev_state, .{
                .waiters = prev_state.waiters - 1,
                .signals = new_signals,
            }, .monotonic, .monotonic) orelse {
                if (prev_state.signals > 0 and prev_state.signals < prev_state.waiters) {
                    // We kept a signal we are not consuming; wake a remaining waiter for it.
                    _ = cond.epoch.fetchAdd(1, .release);
                    io.futexWake(u32, &cond.epoch.raw, 1);
                }
                return;
            };
        }
    }