# Need help understanding exceptions handling from C extension

**URL:** <https://www.ruby-forum.com/t/need-help-understanding-exceptions-handling-from-c-extension/54036>\
**Category:** Ruby\
**Created:** [February 21, 2006, 7:39am UTC](https://www.ruby-forum.com/t/need-help-understanding-exceptions-handling-from-c-extension/54036 "2006-02-21T07:39:52Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Jacob\_Repp](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/848f3c/32.png) [@Jacob\_Repp](https://www.ruby-forum.com/u/Jacob_Repp)\
**Post date:** [February 21, 2006, 7:39am UTC](https://www.ruby-forum.com/t/need-help-understanding-exceptions-handling-from-c-extension/54036/1 "2006-02-21T07:39:52Z")

</div>

I’m working on the test cases for my AIO extension library on windows  
and I have been running into this error consistently on one of my  
tests:

test\_addr\_lookup\_name\_async(ClientTest):  
ArgumentError: NULL pointer given  
tc\_client.rb:129:in `to_s' tc_client.rb:129:in`test\_addr\_lookup\_name\_async’

The offending line is in the rescue block:

```
  begin
        q = AIOQueue.new
        a = AIOAddr.new(q)
        c = Callback.new
        n = 0

        assert(a.is_attached?, "should be attached")
        a.lookup("www.google.com", c, :lookup_complete)

        5.times { n += q.process(100) }

        assert(c.lookups == 1, "didn't receive lookup callback")
        assert(n == 1, "not enough contexts processed")
    rescue Exception => ex
        puts "caught #{ex}"
    end

```

The exception is raised from q.process which hooks directly to a C  
functions and makes another function call to an internal API I  
defined. In this code I have my async context handler:

```
      case CTX_ADDR_LOOKUP:
            rb_funcall(
                    pctx->recvr,
                    pctx->symbid,
                    1,

```

UINT2NUM(((Address\*)(pctx-\>pbase))-\>addr.sin\_addr.s\_addr));

I believe this is ‘raising’ an exception. I see in other extensions  
the usage of rb\_protect() etc. I am under the impression that setjmp,  
longjmp is being used to simulate exceptions in ruby, of which I’m  
unfortunately not an expert in the usage.

I would like to be able to call out to ruby code without losing my  
instruction pointer so that I may deliver the error to a registered  
async error facility.

If someone could smack me over the head with a clue-by-four right now  
that would be most appreciated 😉

Of course I will continue learning and experimenting but I thouht this  
would be a good time to solicit the knowledge of ruby-talk.

---

<div class="post-metadata">

**Author:** ![Jacob\_Repp](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/848f3c/32.png) [@Jacob\_Repp](https://www.ruby-forum.com/u/Jacob_Repp)\
**Post date:** [February 21, 2006, 8:34am UTC](https://www.ruby-forum.com/t/need-help-understanding-exceptions-handling-from-c-extension/54036/2 "2006-02-21T08:34:18Z")

</div>

I caught the exception using rb\_protect() but there is still a problem:

rbaio.c(1279): ruby error: NoMethodError: ???  
rbaio.c(1292): from tc\_client.rb:125:in `process' rbaio.c(1292): from tc_client.rb:125:in`test\_addr\_lookup\_name\_async’

The class name I can interpret okay but when I take $! and call the  
to\_s method on it I get another exception because of the NULL issue. I  
don’t yet know why that is the case.

```
lasterr = rb_gv_get("$!");

// class and message
klass = rb_class_path(CLASS_OF(lasterr));
//message = rb_obj_as_string(lasterr);
DBG2("ruby error: %s: %s", RSTRING(klass)->ptr,

```

“???”);//RSTRING(message)-\>ptr);

Uncommenting the conversion to string results in the NULL error.