debugging on os x

I have a fastcgi app written in C++, multithreaded using fastcgiapp api.  I
am on OS X, and installed apache and fastcgi via darwinports.  Usually
everything works well.

I would like to be able to use GDB from time to time (say if it is crashing,
to find out what line it crashes on).  I haven't had success with this
however, as whenever I attach the debugger, the application just hangs (i.e.
does not send an http response).

Here's what I tried.  First I modified my code a bit to make it single
threaded, since that seems less likely to confuse the debugger than if I run
it with multiple threads, as I normally do.

Then I check that it works, in terms of sending it a request from a
browser.  A-ok.

I check the process id of my app, and then start the debugger as follows:

sudo gdb /opt/local/apache2/fastcgi-bin/myfastcgiapp 6051

It tells me it attaches, and then I can confirm that all is well by doing a
backtrace:

(gdb) bt
#0  0x9005bd18 in accept ()
#1  0x00048cc4 in OS_Accept (listen_sock=0, fail_on_intr=0,
webServerAddrs=0x0) at os_unix.c:1166
#2  0x000469b0 in FCGX_Accept_r (reqDataPtr=0xbffffc4c) at fcgiapp.c:2196
#3  0x00003800 in workerThread (dataP=0xbffffcf0, threadId=0) at
MyFastcgiApp.cpp:244
#4  0x00003ca8 in main (argc=1, argv=0xbffffeb4) at MyFastcgiApp.cpp:369

Looks like what I'd expect.

But now I hit it again with the browser, and it just hangs, and eventually
Apache gives me an "internal server error" page.  I get no indication there
has been a crash either, since normally, if my app crashes the signal
handler will write something to a log file.

Also if I modify my code so that it will crash on a request, I get nothing
(I don't think it gets that far).

Any ideas?  Is there a better way to do this? (other than print statements
to the log file....been doing that for a long time and its gotten really
really old! :) )

Thanks in advance,
-rob

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