CancelStatus

    const CancelStatus = packed struct(u32) {
        requested: bool,
        awaiting: Awaiting,

        const unrequested: CancelStatus = .{ .requested = false, .awaiting = .nothing };

        const Awaiting = enum(u31) {
            nothing = std.math.maxInt(u31),
            group = std.math.maxInt(u31) - 1,
            /// An io_uring fd.
            _,

            fn subWrap(lhs: Awaiting, rhs: Awaiting) Awaiting {
                return @fromBackingInt(@intCast(@backingInt(lhs) -% @backingInt(rhs)));
            }

            fn fromIoUringFd(fd: fd_t) Awaiting {
                const awaiting: Awaiting = @fromBackingInt(@intCast(fd));
                switch (awaiting) {
                    .nothing, .group => unreachable,
                    _ => return awaiting,
                }
            }

            fn toIoUringFd(awaiting: Awaiting) fd_t {
                switch (awaiting) {
                    .nothing, .group => unreachable,
                    _ => return @backingInt(awaiting),
                }
            }
        };

        fn changeAwaiting(
            cancel_status: *CancelStatus,
            old_awaiting: Awaiting,
            new_awaiting: Awaiting,
        ) bool {
            const old_cancel_status = @atomicRmw(CancelStatus, cancel_status, .Add, .{
                .requested = false,
                .awaiting = new_awaiting.subWrap(old_awaiting),
            }, .monotonic);
            assert(old_cancel_status.awaiting == old_awaiting);
            return old_cancel_status.requested;
        }
    }