Re: avoiding copy - Luajit FFI

[Justin Cormack <justin@...>]

On Tue, Jun 7, 2011 at 3:54 PM, Fabio Kaminski <fabiokaminski@gmail.com> wrote:

Hi Folks,

Im trying to get less memory copy as possible with luajit FFI, and in
the api to get your hands in a (void *) or (char *) pointer
is copying it through "ffi.string()" wich in turns, will create a lua string..

my first question: why cant ffi.string() reuse the given pointer.. vm
design? avoid concurrency races  from the C side?

the c api "lua_pushlstring()" works the same way?

second:

When you simply need to push a string or even a file buffer thats
fine, but if whe are talking about things like byte buffers over a
network
those copy would make it loose a lot of performance in the long run..
even creating a bytebuffer on the C side and passing only the
requested byte string on the lua api side..

Anyone has found a way (writing c logic or not) to avoid those copies?

Only call ffi.string when you absolutely need to, the rest of the time you can just pass around the raw buffers. You can just allocate them with ffi.new.

Justin