Re: small problem with LuaJIT FFI and gc method
[
Date Prev][
Date Next][
Thread Prev][
Thread Next]
[
Date Index]
[
Thread Index]
- Subject: Re: small problem with LuaJIT FFI and gc method
- From: Francesco Abbate <francesco.bbt@...>
- Date: 2011年3月16日 10:08:38 +0100
Hi Mike,
I was finally able to reproduce and understand the problem. It was
actually a very subtle error related to matrices/vectors and not to
permutations.
The solution I've adopted is a little bit ugly so I was willing to
have you point of view to see if I can get something better.
A very short background, the GSL library does defines the types for
gsl_vector and gsl_matrix and two related types, gsl_vector_view and
gsl_matrix_view. Here the relevant cdefs:
----------------
typedef struct {
size_t size;
double * data;
} gsl_block;
typedef struct {
size_t size;
size_t stride;
double * data;
gsl_block * block;
int owner;
} gsl_vector;
typedef struct {
size_t size1;
size_t size2;
size_t tda;
double * data;
gsl_block * block;
int owner;
} gsl_matrix;
typedef struct {
gsl_vector vector;
} gsl_vector_view;
typedef struct {
gsl_matrix matrix;
} gsl_matrix_view;
--------------------
Here what I was doing in my code, basically creating a matrix as a
userdata object with gsl.new, take a matrix_view to it to have a cdata
object to the same underlying data and then storing the cdata and its
related usedata matrix in a Lua table.
Here the code:
local M = { _data = {} }
-- map cdata objects to its related userdata object
-- useful both for lookup and to prevent premature disposing of userdata
local function store(obj, cdata)
local t = M._data
t[cdata] = obj
return cdata
end
-- related table lookup
local function object(cdata)
local t = M._data
return t[cdata]
end
local function get_matrix(n1, n2)
local m = gsl.new(n1, n2)
local s = cgsl.gsl_matrix_submatrix (m, 0, 0, n1, n2)
return store(m, s.matrix)
end
local function get_vector(nr)
local m = gsl.new(nr, 1)
local v = cgsl.gsl_matrix_column (m, 0)
return store(m, v.vector)
end
---------------------
So it seems that the problem was that I was indexing with the cdata
s.matrix while the original cdata was 's' itself. I guess that Lua was
disposing of the original memory allocated for 's' because it was not
referenced.
Here the solution that I found:
------------------
local M = { _data = {} }
local function store(obj, ckey, cdata)
local t = M._data
t[ckey] = obj
t[#t+1] = cdata
return ckey
end
local function object(cdata)
local t = M._data
return t[cdata]
end
local function get_matrix(n1, n2)
local m = gsl.new(n1, n2)
local s = cgsl.gsl_matrix_submatrix (m, 0, 0, n1, n2)
return store(m, s.matrix, s)
end
local function get_vector(nr)
local m = gsl.new(nr, 1)
local v = cgsl.gsl_matrix_column (m, 0)
return store(m, v.vector, v)
end
-----------------------------
This solution seems to *really* solve the problem.
Mike, could you confirm my analysis of the problem ? Could you suggest
a better solution to what I've found or may be give some general
recommendations ?
Thanks in advance for any help.
Francesco