[boost] [future] Integrating recent future lib into old-ish threadpool lib

10 May 2008

      There's a nice threadpool library (http://threadpool.sourceforge.net)
mentioned on a previous thread that I took a look at and noticed it
had a basic future impl. of its own. Given that there's a future
library under review, I swapped out the original future impl. in the
schedule function, plus added a lazy_schedule (from the examples @
http://braddock.com/~braddock/future/ ) for fun.

I replaced everything in future.hpp from the threadpool lib with:

/*
* Copyright (c) 2005-2007 Philipp Henkel
*
* Use, modification, and distribution are  subject to the
* Boost Software License, Version 1.0. (See accompanying  file
* LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
*
* http://threadpool.sourceforge.net
*
* Chris Fairles, May 2008 - Modified to replace custom future
implementation with boost-reviewed version
*/
#pragma once
#include <boost/future/future.hpp>

namespace boost { namespace threadpool
{

template<class Pool, class F>
future<typename result_of< F() >::type>
schedule(Pool& pool, F const& task)
{
	typedef typename result_of< F() >::type result_type;

	promise<result_type> prom;
	pool.schedule(future_wrapper<result_type>(task, prom));

	return future<result_type> (prom);
}

template<class Pool, class F>
future<typename result_of< F() >::type>
lazy_schedule(Pool& pool, F const& task)
{
	typedef typename result_of< F() >::type result_type;

	promise<result_type> prom;
	future<void> guard = prom.get_needed_future();
	guard.add_callback(bind(&Pool::schedule, pool,
            future_wrapper<result_type>(task, prom)));

	return future<result_type> (prom);
}

} } // namespace boost::threadpool

where #include <boost/future/future.hpp> is the header for the lib
under review (and pardon the pragma windowism).

I haven't tested it throughly but on msvc9, the most trivial of cases
work (including catching exceptions) so YMMV.

Ex.

int task_int_1() {
  throw std::exception("task_int_1 exception");
  return 1;
}

int task_int_2() {
  return 2;
}

int main() {
  pool tp;
  tp.size_controller().resize(2);

  future<int> result1 = schedule(tp, &task_int_1);
  future<int> result2 = schedule(tp, &task_int_2);

  try {
    int val = result1 + result2;
    std::cout << "you will never see this value... " << val << std::endl;
  } catch (std::exception const& ex)  }
    std::cerr << ex.what() << std::endl;
  }
}

Something to play around with anyway.

Cheers,
Chris