From: Jacob Repp <jacobrepp@...>
Date: 2006-02-21T15:37:09+09:00
Subject: Need help understanding exceptions handling from C extensions

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.