parallel.hpp

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/*
 * Copyright (c) 2018 The BitShares Blockchain, and contributors.
 *
 * The MIT License
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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#pragma once
 
#include <fc/thread/task.hpp>
#include <fc/thread/thread.hpp>
#include <fc/asio.hpp>
 
#include <boost/atomic/atomic.hpp>
 
namespace fc {
 
   namespace detail {
      class pool_impl;
 
      class worker_pool {
      public:
         worker_pool();
         ~worker_pool();
         void post( task_base* task );
      private:
          pool_impl*    my;
      };
 
      worker_pool& get_worker_pool();
   }
 
   class serial_valve {
   private:
      class ticket_guard {
      public:
         explicit ticket_guard( boost::atomic<future<void>*>& latch );
         ~ticket_guard();
         void wait_for_my_turn();
      private:
         promise<void>::ptr my_promise;
         future<void>*      ticket;
      };
 
      friend class ticket_guard;
      boost::atomic<future<void>*> latch;
 
   public:
      serial_valve();
      ~serial_valve();
 
      template<typename Functor1,typename Functor2>
      auto do_serial( const Functor1& f1, const Functor2& f2 ) -> decltype(f2())
      {
         ticket_guard guard( latch );
         f1();
         guard.wait_for_my_turn();
         return f2();
      }
   };
 
   template<typename Functor>
   auto do_parallel( Functor&& f, const char* desc FC_TASK_NAME_DEFAULT_ARG ) -> fc::future<decltype(f())> {
      typedef decltype(f()) Result;
      typedef typename std::remove_const_t< std::remove_reference_t<Functor> > FunctorType;
      typename task<Result,sizeof(FunctorType)>::ptr tsk =
         task<Result,sizeof(FunctorType)>::create( std::forward<Functor>(f), desc );
      tsk->retain(); // HERE BE DRAGONS
      fc::future<Result> r( std::dynamic_pointer_cast< promise<Result> >(tsk) );
      detail::get_worker_pool().post( tsk.get() );
      return r;
   }
}