Re: [Boost-users] [Boost.thread] Exception handling strategy ?

From: vicente.botet (vicente.botet_at_[hidden])
Date: 2008-07-21 12:55:04

----- Original Message ----- 
From: "Anthony Williams" <anthony.ajw_at_[hidden]>
To: <boost-users_at_[hidden]>
Sent: Thursday, July 17, 2008 11:21 AM
Subject: Re: [Boost-users] [Boost.thread] Exception handling strategy ?

>
> "Emil Dotchevski" <emil_at_[hidden]> writes:
>
>> Yes this should be easy, I'll do it after 1.36 ships.
>
> Excellent!

If I understood, the MSVC-specific code allows the user to get the current 
exception without throwing the exception with 
boost::enable_current_exception(). What is the advantage if we can not 
profit of this mechanism with other compilers?

A few months ago I proposed an intrusive way allowing the user to define 
which exceptions where wrapped by boost::exception_ptr. IMHO, the 
exception_ptr emulation (without language support) to transport exceptions 
between threads is not of real use if the user can not configurate the 
exceptions that can be thrown by 3pp as the Exception library do already for 
the STL exceptions.

If the Exception library do not allow this, how can the Future library 
transport every exception between two threads?

For recall, my proposal was the following:
The exception library defines a macro such as:

#define BOOST_EXCEPTION_CATCH_RETURN(EXCP) \
catch( EXCP & e ) { \
return exception_detail::current_exception_unknown_boost_exception(e); \
}

The current_exception function has a USER_SLOT used us follows

inline exception_ptr
current_exception()
{
    try
    {
        throw;
    }
    catch(
        exception_detail::cloning_base & e )
    {
        exception_detail::clone_base const * c = e.clone();
        BOOST_ASSERT(c!=0);
        return exception_ptr(c);
    }
    catch(
        std::invalid_argument & e )
    {
        return exception_detail::current_exception_std_exception(e);
    }
    // ... as before
#ifdef BOOST_EXCEPTION_USER_SLOT
#include BOOST_EXCEPTION_USER_SLOT
#endif
    catch( ... )
    {
        return exception_detail::current_exception_unknown_exception();
    }
}

The user can define BOOST_EXCEPTION_USER_SLOT to a file containing one line 
for each exception that must be transported:

BOOST_EXCEPTION_CATCH_RETURN(3pp::exception1)
BOOST_EXCEPTION_CATCH_RETURN(boost:lock_error)

Of course this has a limitation: it works only if the function using the 
current_exception is also inlined.

Best,

Vicente