condSignal

fn condSignal(cond: *Io.Condition) void {
    var prev_state = cond.state.load(.monotonic);
    while (prev_state.waiters > prev_state.signals) {
        @branchHint(.unlikely);
        prev_state = cond.state.cmpxchgWeak(prev_state, .{
            .waiters = prev_state.waiters,
            .signals = prev_state.signals + 1,
        }, .release, .monotonic) orelse {
            // Update the epoch to tell the waiting threads that there are new signals for them.
            // Note that a waiting thread could miss a take if *exactly* (1<<32)-1 wakes happen
            // between it observing the epoch and sleeping on it, but this is extraordinarily
            // unlikely due to the precise number of calls required.
            _ = cond.epoch.fetchAdd(1, .release); // `.release` to ensure ordered after `state` update
            Thread.futexWake(&cond.epoch.raw, 1);
            return;
        };
    }
}