Re: [boost] [exception][policy]

From: Emil Dotchevski (emil_at_[hidden])
Date: 2008-08-31 14:59:31

On Sun, Aug 31, 2008 at 8:54 AM, vicente.botet <vicente.botet_at_[hidden]> wrote:
>> On Sat, Aug 30, 2008 at 7:21 PM, vicente.botet <vicente.botet_at_[hidden]>
>> 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:
>
> 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?

I didn't mean anything in particular, I just wanted to understand the
problem you are trying to solve. :)

Your function wrapper solution is a possibility. Another possibility
is, if the thread pool library is not third party, it can implement
your original idea of exception registry.

Such use cases are supported by boost::copy_exception:

catch( something & x )
{
  boost::exception_ptr p=boost::copy_exception(x);
  ...
}

Note however that after an exception is thrown without using
boost::enable_current_exception, it is already too late for a general
solution because it might be unsafe or impossible to copy the type you
catch. For example, this will not work:

catch( boost::exception & x )
{
  boost::exception_ptr p=boost::copy_exception(x);
}

You'd get a compile error, because boost::exception is abstract.

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode