Re: [snabb-devel] LuaJIT-friendly API and data structure design
- From: Justin Cormack <justin@xxxxxxxxxxxxxxxxxxxxx>
- To: snabb-devel@xxxxxxxxxxxxxxxx
- Date: Thu, 19 Feb 2015 14:47:40 +0000
On 19 February 2015 at 13:54, Luke Gorrie <luke@xxxxxxxx> wrote:
> This pointer arithmetic can also lead to allocation, and it would be nice to
> avoid that. The approach that comes to mind is to require a reusable box
> (struct tcp *[1]) to be provided:
>
> function tcp_header (packet, box)
> box[0] = ffi.cast(tcp_t, packet.data + tcp_offset(packet.data))
> end
>
> and maybe this is actually the basis for a general solution. I don't enjoy
> this specific "[0]" syntax so much but perhaps we could wrap it up in a Lua
> object nicely.
>
> (Again, Alex is already ahead of me on this track, and I am catching up from
> first principles.)
What I did for ljsyscall was to allow you to pass boxes to all
functions but to make them optional ie
function tcp_header (packet, box)
box = box or ffi.new(tcp_t_1)
box[0] = ffi.cast(tcp_t, packet.data + tcp_offset(packet.data))
return box
end
(I have named types for the boxes as there are not many of them)
This way the user who doesnt care need to allocate a box, but the user
who wants to can, but the interface is still the same because it
returns the box anyway.
Justin
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- » Re: [snabb-devel] LuaJIT-friendly API and data structure design - Justin Cormack
