Re: [boost] Has someone any plans to submit a exception_ptr library to Boost?

From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2008-04-20 15:07:23

Frank Mori Hess wrote:
> Here's a partial proof-of-concept implementation of exception_ptr for
> Linux, tested on gcc 4.1.2.
Have you tested this case:

void fn()
{
  exception_ptr p;
  try {
    throw runtime_error("hello, world");
  } catch(...) {
    p = current_exception();
  }
  rethrow_exception(p);
}

int main()
{
  try {
    fn();
  } catch(runtime_error &e) {
    std::cerr << e.what() << '\n';
  }
}

I believe your scheme will delete the exception object when p goes out 
of scope, so either the exception mechanism itself will crash, or e will 
be dangling.
Testing this out proves it. If I add some output statements, I get:

Rethrowing.
virtual test_exception::~test_exception()
Caught in main.

Even though it happens not to crash my simple scenario, it shows clearly 
that the exception is destructed before it is caught in main.

This is still too simple, unfortunately. Replacing the cleanup function 
is a good idea, but it's not enough to get around the limitations of 
this method. I played around with it all day today.

I'm currently trying my next play: I need more data reachable from the 
exception object, so I'm going to make it reachable. My plan is to let 
the cleanup function pointer point to a structure whose first bytes 
contain the code of a function that simply returns. In other words, I 
hide more data behind the cleanup function. Wish me luck. :-)

Sebastian