Rb_raise() causes segmentfault on xxxxx_alloc() function

Ruby
1

Hi, my C extension uses rb_define_alloc_func(cResolver,
Resolver_alloc) to initialite the C library. If something goes wrong
in that initialization I want to raise an exception but using
rb_raise() within Resolver_alloc() produces a segmentfault.

The function is very easy:

VALUE Resolver_alloc(VALUE klass)
{
struct dns_ctx *dns_context;
VALUE obj;

if (dns_init(NULL, 0) < 0)
rb_raise(rb_eStandardError, “udns dns_init failed”);

if (!(dns_context = dns_new(NULL)))
rb_raise(rb_eStandardError, “udns dns_new failed”);

obj = Data_Wrap_Struct(klass, NULL, Resolver_free, dns_context);
return obj;
}

In order to force the error I change the dns_init line as follows:

if (dns_init(NULL, 0) == 0)

and get a segmentfault. Is not allowed to raise an exception in the
alloc function of a class?

Thanks.

2

On Mon, 7 Feb 2011 11:32:17 +0900
Iñaki Baz C. [email protected] wrote:

struct dns_ctx *dns_context;
}
Thanks.

I’m not exactly sure how this mechanism works (and udns too), but I’d
suggest:
a) If a C library needs an one-time initialization, implement that as a
class method of your Resolver class and call either on library loading
or on first use of the library (by defining a flag).
b) If a C library needs an initialization for each instance of the
object, just define initialize function for the class and do all the
initialization there; if you strictly need to do that in *_alloc
function(), try returning Qnil (I am not quite sure it will work at
all, but at least it’s worth trying), or set a flag in the structure
you are returning. Either way will let you to determine whether to
raise an exception or not in the place where it’s perfectly safe to do
that (the initialize function).

It looks to me that you need both approaches here.

3

2011/2/7 Peter Z. [email protected]:

you are returning. Either way will let you to determine whether to
raise an exception or not in the place where it’s perfectly safe to do
that (the initialize function).

It looks to me that you need both approaches here.

Thanks a lot. I just need second approach as initialization of the C
library must occur for each instance.

I already tryed returning Qnil, and gives an ugly error:
`new’: wrong instance allocation (TypeError)

So I took your second suggestion, but instead I set an attribute
@alloc_error during xxxx_alloc() function, and inspect it in normal
initialize() method (by raising if it is not nil).

Thanks a lot!