Exception propagation to parent thread.

Hello all,

I have come up with some code that allows non-clone-able objects to be
propagated, without slicing, in to the "parent thread" upon join() or
materialisation of a future etc. I was spurred on by a discussion in
this thread on comp.programming.threads:
http://groups.google.co.uk/group/comp.programming.threads/msg/9698784456fc9b75?hl=en

The static types of the exceptions to be caught must be registered with
the thread (object) before running its "body". Here's some example
code:

// This function will form the "body" of the thread
double throw_happy()
{
     throw std::runtime_error("BANG!");
     return 0;
}

int main()
{
     thread<double> t(throw_happy);

     // The following two statements can be re-ordered without
     // changing the outcome. Exceptions that have these exact
     // *static* types will be propagated. Any other exceptions
     // caught inside the thread are turned in to an exception of
     // a special type (uncaught_thread_exception in my code).

     t.enable_propagate<std::runtime_error>();
     t.enable_propagate<std::exception>();

     try
     {
         t.run();
         std::cout << "Thread is running..." << std::endl;
         double d = t.join();
     }
     catch(const std::runtime_error &ex)
     {
         std::cerr << ex.what() << '\n';
     }

     return 0;
}

Output:
------------
Thread is running...
BANG!
------------

The full code is here: http://www.nunswithguns.net/guff/propagate.cpp

I'm pretty sure the code could be modified to factor out a
catch/copy/storage policy for each registered type to allow
clone()-able types to be "caught polymorphically" and propagated, too.

Perhaps this has been done before, but I haven't come across it (the
non-slicing-static-type stuff, that is -- I've seen this for
clone()-able hierarchies). It's certainly not perfect, but I thought
I'd throw it out there for the sake of discussion. I know I might well
end up using something like this in the near future.

What do others think?

Kind regards,

Edd

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