[Boost-users] Throwing an exception in a packaged_task: is there a clear example?

[Mark Wilson]

Hello,

I am throwing an exception from a packaged_task, and then trying to catch it with f.get() (where f is a unique_future); it doesn't work, the program just terminates with:

terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::unknown_exception>'
  what():  std::exception


Is there a simple example somewhere, or could someone provide one, that makes clear how this mechanism is supposed to work?  The Threads documentation does not show how to do this...

Here is my simple program, based on the example in the docs:

#include <boost/thread.hpp>
#include <boost/thread/future.hpp>
#include <boost/exception/all.hpp>

struct MyException
{
    MyException()
    {
    }
};

int calculate_the_answer_to_life_the_universe_and_everything()
{
    throw MyException();
    return 42;
}

int main()
{
    boost::packaged_task<int>
        task(calculate_the_answer_to_life_the_universe_and_everything);
    boost::unique_future<int> f(task.get_future());

    boost::thread t(boost::move(task));

    try
    {
        f.get();
    }
    catch(MyException& ex)
    {
        std::cout << "EXCEPTION!" << std::endl;
    }
}

Thanks,
Mark Wilson

[Emil Dotchevski]

On Thu, Aug 19, 2010 at 8:54 AM, Mark Wilson <mw...@lle.rochester.edu> wrote:
> Hello,
>
> I am throwing an exception from a packaged_task, and then trying to catch it
> with f.get() (where f is a unique_future); it doesn't work, the program just
> terminates with:
>
> terminate called after throwing an instance of
> 'boost::exception_detail::clone_impl<boost::unknown_exception>'
>   what():  std::exception
>
>
> Is there a simple example somewhere, or could someone provide one, that
> makes clear how this mechanism is supposed to work?  The Threads
> documentation does not show how to do this...

Try replacing throw MyException with
BOOST_THROW_EXCEPTION(MyException()). You'll need to #include
<boost/throw_exception.hpp>.

The page at http://beta.boost.org/doc/libs/release/libs/exception/doc/current_exception.html
explains why you get a boost::unknown_exception.

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

Thank you, Emil.   That works.