waitUncancelable

    pub fn waitUncancelable(cond: *Condition, io: Io, mutex: *Mutex) void {
        var epoch = cond.epoch.load(.acquire); // `.acquire` to ensure ordered before state load

        {
            const prev_state = cond.state.fetchAdd(.{ .waiters = 1, .signals = 0 }, .monotonic);
            assert(prev_state.waiters < math.maxInt(u16)); // overflow caused by too many waiters
        }

        mutex.unlock(io);
        defer mutex.lockUncancelable(io);

        while (true) {
            io.futexWaitUncancelable(u32, &cond.epoch.raw, epoch);

            epoch = cond.epoch.load(.acquire); // `.acquire` to ensure ordered before `state` laod

            // Even on error, try to consume a pending signal first. Otherwise a race might
            // cause a signal to get stuck in the state with no corresponding waiter.
            {
                var prev_state = cond.state.load(.monotonic);
                while (prev_state.signals > 0) {
                    prev_state = cond.state.cmpxchgWeak(prev_state, .{
                        .waiters = prev_state.waiters - 1,
                        .signals = prev_state.signals - 1,
                    }, .acquire, .monotonic) orelse {
                        // We successfully consumed a signal.
                        return;
                    };
                }
            }

            // There are no more signals available; this was a spurious wakeup,
            // so we'll loop back to the futex wait.
        }
    }