I'm trying to implement a standard gsl_rng_type that is
backed by a file. The file should be opened when the
gsl_rng is created, a clone needs to dup() the file handle
and copy the file offset, and the file needs to be closed
when gsl_rng_free() is called.
For rng creation, gsl_rng_alloc() calls gsl_rng_type->set()
with a freshly malloc()ed "state" area. Since the area is
uninitialized memory, one can't use it directly as a flag to
see if set() has been called before on this particular
rng_type.
Cleanup is also a problem. The gsl_rng_free() directly
calls free() on both the state and gsl_rng itself. This
means there is no obvious way to force the close needed to
clean up after a file-backed rng.
I don't see any clean way of implementing something like
this without adding a callback or two to gsl_rng_type.
Something like this might work:
typedef struct
{
gsl_rng_type base
void* create_state(const void* clone);
destroy_state(void* state);
}
gsl_rng_extended_type;
The argument to create_state() would let the code
distinguish between a new state object (NULL == clone) and
one being created through a call to gsl_rng_clone() (NULL !=
clone).
The library code could default to the old behavior if size >
0, but use the new callbacks if 0 == size. (Are there any
existing implementations that have a zero size?)
Any thoughts on this matter?
Thanks.
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