[Boost-bugs] [Boost C++ Libraries] #8955: Request for more efficient way to get exception_ptr from future

Subject: [Boost-bugs] [Boost C++ Libraries] #8955: Request for more efficient way to get exception_ptr from future
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-08-01 23:38:49

#8955: Request for more efficient way to get exception_ptr from future
------------------------------+--------------------------
 Reporter:  ned14             |      Owner:  anthonyw
     Type:  Feature Requests  |     Status:  new
Milestone:  Boost 1.55.0      |  Component:  thread
  Version:  Boost 1.54.0      |   Severity:  Optimization
 Keywords:                    |
------------------------------+--------------------------
 Vicente,

 Here is that Boost.Thread feature request for AFIO I mentioned a while
 ago. Here is the code example:

 {{{
                 shared_future<std::shared_ptr<detail::async_io_handle>>
 *thisresult=state.first->outsharedstates[idx].get();
                 // This seems excessive but I don't see any other legal
 way to extract the exception ...
                 bool success=false;
                 try
                 {
                         // Always must wait on the others, because some
 may be between decrementing the
                         // atomic and returning their result to here. Any
 waiting is likely short.
                         thisresult->get();
                         success=true;
                 }
                 catch(...)
                 {
                         exception_ptr
 e(afio::make_exception_ptr(afio::current_exception()));
                         assert(e);
                         complete_async_op(s.out[idx].first,
 s.out[idx].second, e);
                 }
                 if(success)
                         complete_async_op(s.out[idx].first,
 s.out[idx].second);
 }}}

 Taken from
 https://github.com/BoostGSoC/boost.afio/blob/master/libs/afio/src/afio.cpp#L1027


 Basically, we need to scan a sequence of futures for any exception states
 which right now means trying to get() from each and try...catch to grab
 any exception_ptr's. As this is inefficient, is there any chance of adding
 a new member function to future and shared_future: get_exception()? This
 is identical to get(), except it returns any exception state instead of
 throwing it. If there is no exception state, it returns a null
 exception_ptr.

 In other words, a very simple new feature, but one which lets us eliminate
 a lot of needless try...catch stanzas.

 My thanks in advance Vicente.

 Niall

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/8955>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.