----- Original Message ----- From: "Emil Dotchevski" <emil@revergestudios.com> To: <boost@lists.boost.org> Sent: Sunday, August 31, 2008 5:30 AM Subject: Re: [boost] [exception][policy]
On Sat, Aug 30, 2008 at 7:21 PM, vicente.botet <vicente.botet@wanadoo.fr> wrote:
What use case do you have in mind?
Sorry, but I dont understand your question. What use case do I have in mind for what? Maybe you can question is related to:"What is worst is that the final user can not do anything for the exceptions thrown by 3pp libraries that do not use boost::enable_current_exception or boost::throw_exception."
I am trying to be as objective as possible in answering your previous questions. For that, I need to understand what is the use case you have in mind. I understand that it involves a 3rd party library throwing an exception, but more details please:
Emil, My own application request a thread pool library to execute a function F asynchronously
- who catches the exception initially?
A thread pool (packaged_task) library, which calls the function F calling a 3pp function 3ppF throwing an exception (3pp_exception1 or 3pp_exception2)
- who copies it into an exception_ptr?
the same thread pool (packaged_task) library calls the current_exception and stores the exception_ptr in the future associates to the packaged task.
- who rethrows it?
The thread pool (packaged_task) Library which rethrow the stored exception when the user wait on the future value.
- who catches it after the rethrow?
My own application, which requested a thread pool library to execute the function F Emil, while answering your question I see that I was wrong when I said that "final user can not do anything for the exceptions thrown by 3pp libraries": The final user can define a function Ftry_catch wich wraps the call to the function F by a try-catch, use the boost:throw_exception to throw each one of the exceptions 3ppF can throw, and request the thread pool library to execute the function Ftry_catch instead. Was this what you mean? Do you think that it is raisonable that every user of the thread_pool library must wraps each packaged_task function in order to ensure that the exception are transported between threads? Should the user be aware of which compilers don't need this wrapping because current_exception works for every exception? What do you think about a functor class that do all this stuff, something like (not correct C++ code)? template <result_type (*FUNCTION)(arg1_type, ..., argk_type), typename EXCP1, ..., typename EXCPN> class try_catch { public: result_type operator()(arg1_type p1, ..., argk_type pk) { try { return FUNCTION(p1, ..., pk); } catch (EXCP1& e) { boost::throw_exception(e); ... } catch (EXCPN& e) { boost::throw_exception(e); } catch (...) { throw; } } }; try_catch<F, 3pp_exception1, 3pp_exception2> Ftry_catch; packaged_task(Ftry_catch); Thanks, Vicente