Re: [Boost-users] Unable to catch exception using boost::asio

Subject: Re: [Boost-users] Unable to catch exception using boost::asio
From: Alex Black (alex_at_[hidden])
Date: 2009-07-15 11:22:09

(Response below)

> 
> Alex Black wrote:
> > (Response is below)
> > 
> >  
> >> On Tue, Jul 14, 2009 at 7:49 PM, Alex 
> Black<alex_at_[hidden]> wrote:
> >>>>> I'm using boost::asio for sockets, writing a response out to a
> >>> client.
> >>>>> If the client stops part way through getting the 
> >> response, then my 
> >>>>> server process dies:
> >>>>>
> >>>>> terminate called after throwing an instance of
> >>>>>
> >> 
> 'boost::exception_detail::clone_impl<boost::exception_detail::error_in
> >>>>> fo_injector<boost::system::system_error>
> >>>>>> '
> >>>>> ? what():? Broken pipe
> >>>>>
> >>>>> The code though is surrounded by try catch like this:
> >>>>>
> >>>>> try
> >>>>> {
> >>>>> ??? ...
> >>>>> }
> >>>>> catch ( std::exception& e )
> >>>>> {
> >>>>> ??? cout << e.what() << endl;
> >>>>> }
> >>>>> catch ( ... )
> >>>>> {
> >>>>> ???? cout << "unexpected exception" << endl; }
> >>>>>
> >>>>> How do I prevent my process from aborting/terminating like this?
> >>> v
> >>>
> >>>> Have you verified that the code inside the try block 
> executes on the
> >>> same thread that the exception is occuring in?
> >>>
> >>> Not explicitly, how would I do that?
> >>>
> >>> thx
> >>>
> >> First put a breakpoint inside the try block.  When it gets 
> >> hit use whatever mechanism your debugger provides to see what 
> >> thread you're in.  In windows using MSVC, for example, you'd 
> >> just add a watch for a variable called $TID which a special 
> >> pseudo-variable that shows you the thread id.  For other 
> >> debuggers you'd have to consult the manual.
> >>  Next register an unhandled exception handler.
> >>
> >> #include <exception>
> >>
> >> void unhandled_exception_handler()
> >> {
> >>    std::cout << "Got an unhandled exception!" << std::endl; }
> >>
> >> int main(int argc, char** argv)
> >> {
> >>    std::set_terminate(unhandled_exception_handler);
> >>
> >>    //rest of your program.
> >> }
> >>
> >> Then put a breakpoint inside unhandled_exception_handler and 
> >> when it gets hit walk up the callstack in the debugger to see 
> >> where the exception is occuring.  In addition you can 
> >> determine the thread id again using the same method you used 
> >> in the first step.  My guess is that they're not in the same 
> >> thread.  I'm not sure if it applies to your scenario, but 
> >> remember that the operation's completion handler is invoked 
> >> on is not necessarily the same thread that the request is 
> >> issued on depending on how you're using the io_service 
> >> object.  So while you have a try {} catch(...) {} in the 
> >> completion handler, if the exception is on the other thread 
> >> that does you no good.
> >>
> > 
> > Thanks for the tip, I didn't know about set_terminate, I made that
> > change.
> > 
> > I put a breakpoint in my terminate handler, and the callstack looks
> > like:
> > 
> > 32 unhandled_exception_handler() /home/noirs/workspace/myfile.cpp:35
> > 0x0000000000438764	
> > 31 <symbol is not available> 0x00007f9ceb0d04b6	
> > 30 <symbol is not available> 0x00007f9ceb0cf6ab	
> > 29 __gxx_personality_v0()  0x00007f9ceb0d0278	
> > 28 <symbol is not available> 0x00007f9ceab7cff3	
> > 27 _Unwind_Resume()  0x00007f9ceab7d0b8	
> > 26 ~ProtoBufStreamAdaptor() /home/noirs/workspace/myfile2.cpp:10
> > 0x000000000042c6e5	
> > 25 CWebServer::HandleGetNeighbors()
> > /home/noirs/workspace/myfile3.cpp:215 0x000000000041d2d8	
> > 24 CWebServer::OnHttpRequest() /home/noirs/workspace/myfile3.cpp:89
> > 0x000000000041e790	
> > 23 CBaseWebServer::HandleHTTPRequest()
> > /home/noirs/workspace/myfile4.cpp:92 0x00000000004092ef	
> > 22 CBaseWebServer::HandleAccept() 
> /home/noirs/workspace/myfile4.cpp:61
> > 0x0000000000409a9e	
> > 
> > HandleAccept looks like:
> > 
> > void CBaseWebServer::HandleAccept(shared_ptr<tcp::socket> 
> pSocket, const
> > boost::system::error_code& error)
> > {	if ( !error )
> > 	{
> > 		try
> > 		{
> > 			HandleHTTPRequest(pSocket);
> > 
> > 			StartAccept();
> > 		}
> > 		catch ( ... )
> > 		{
> > 			cout << "Unhandled exception in HandleAccept";
> > 		}
> > 	}
> > 	else
> > 	{
> > 		cout << "HandleAccept received error: " <<
> > error.message().c_str() << endl;
> > 	}
> > }
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> > http://lists.boost.org/mailman/listinfo.cgi/boost-users
> 
> Um, broken pipe = closed file desciptor.
> 
> Check if the socket is actually valid in the shard_ptr...
> 
> BTW, are you using Async operations.... if so then the exception will 
> not originate from your code but from io_service.run().

I wrapped my call to run() in a try-catch, no luck, no exception appears
to be being thrown by io_service.run().

void CBaseWebServer::RunIoService()
{
        try
        {
                m_IoService.run();
        }
        catch ( ... )
        {
                cout << "Unhandled exception in RunIoService";
        }
}