Re: luaL_Buffer and 'exception safety'

[Mike Pall <mikelu-0707@...>]

Hi,

Dirk Feytons wrote:
> I was looking at the luaL_Buffer mechanism. I know it is intended for
> collecting lots of small strings but luaL_prepbuffer() seems useful
> for my scenario. Could I use this to allocate space and pass the
> pointer to the read_data() function, then do a luaL_addsize() and
> luaL_pushresult()? Is it guaranteed that if some Lua function raises
> an error the luaL_Buffer memory is freed?

The luaL_Buffer mechanism uses a fixed size buffer on the C stack
(LUAL_BUFFERSIZE = BUFSIZ = usually 4K or 8K) and pushes partial
Lua strings on the Lua stack if the buffer overflows. No memory
leak can result, since the C stack is just reset on error and Lua
strings are garbage collected.

But this also means you need to split the read into pieces. Have
a look at the read_chars() function in liolib.c. Another subtle
point: you need to keep the Lua stack at the same level before
calling any of the buffer functions (put any slots you need at
fixed positions below the buffer slots).

Bye,
     Mike