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 // Copyright (C) 2013 Vicente J. Botet Escriba
 //
 //  Distributed under 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)
 //
 // 2013/11 Vicente J. Botet Escriba
 //    first implementation of a simple serial scheduler.
 
 #ifndef BOOST_THREAD_USER_SCHEDULER_HPP
 #define BOOST_THREAD_USER_SCHEDULER_HPP
 
 #include <boost/thread/detail/config.hpp>
 #if defined BOOST_THREAD_PROVIDES_FUTURE_CONTINUATION && defined BOOST_THREAD_PROVIDES_EXECUTORS && defined BOOST_THREAD_USES_MOVE
 
 #include <boost/thread/detail/delete.hpp>
 #include <boost/thread/detail/move.hpp>
 #include <boost/thread/concurrent_queues/sync_queue.hpp>
 #include <boost/thread/executors/work.hpp>
 
 #include <boost/config/abi_prefix.hpp>
 
 namespace boost
 {
 
   class user_scheduler
   {
     /// type-erasure to store the works to do
     typedef  executors::work work;
 
     /// the thread safe work queue
     sync_queue<work > work_queue;
 
   public:
     /**
      * Effects: try to execute one task.
      * Returns: whether a task has been executed.
      * Throws: whatever the current task constructor throws or the task() throws.
      */
     bool try_executing_one()
     {
       work task;
       try
       {
         if (work_queue.try_pull(task) == queue_op_status::success)
         {
           task();
           return true;
         }
         return false;
       }
       catch (std::exception& )
       {
         return false;
       }
       catch (...)
       {
         return false;
       }
     }
   private:
     /**
      * Effects: schedule one task or yields
      * Throws: whatever the current task constructor throws or the task() throws.
      */
     void schedule_one_or_yield()
     {
         if ( ! try_executing_one())
         {
           this_thread::yield();
         }
     }
 
 
     /**
      * The main loop of the worker thread
      */
     void worker_thread()
     {
       while (!closed())
       {
         schedule_one_or_yield();
       }
       while (try_executing_one())
       {
       }
     }
 
   public:
     /// user_scheduler is not copyable.
     BOOST_THREAD_NO_COPYABLE(user_scheduler)
 
     /**
      * \b Effects: creates a thread pool that runs closures using one of its closure-executing methods.
      *
      * \b Throws: Whatever exception is thrown while initializing the needed resources.
      */
     user_scheduler()
     {
     }
     /**
      * \b Effects: Destroys the thread pool.
      *
      * \b Synchronization: The completion of all the closures happen before the completion of the \c user_scheduler destructor.
      */
     ~user_scheduler()
     {
       // signal to all the worker thread that there will be no more submissions.
       close();
     }
 
     /**
      * loop
      */
     void loop() { worker_thread(); }
     /**
      * \b Effects: close the \c user_scheduler for submissions.
      * The loop will work until there is no more closures to run.
      */
     void close()
     {
       work_queue.close();
     }
 
     /**
      * \b Returns: whether the pool is closed for submissions.
      */
     bool closed()
     {
       return work_queue.closed();
     }
 
     /**
      * \b Requires: \c Closure is a model of \c Callable(void()) and a model of \c CopyConstructible/MoveConstructible.
      *
      * \b Effects: The specified \c closure will be scheduled for execution at some point in the future.
      * If invoked closure throws an exception the \c user_scheduler will call \c std::terminate, as is the case with threads.
      *
      * \b Synchronization: completion of \c closure on a particular thread happens before destruction of thread's thread local variables.
      *
      * \b Throws: \c sync_queue_is_closed if the thread pool is closed.
      * Whatever exception that can be throw while storing the closure.
      */
 
 #if defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
     template <typename Closure>
     void submit(Closure & closure)
     {
       work w ((closure));
       work_queue.push(boost::move(w));
       //work_queue.push(work(closure)); // todo check why this doesn't work
     }
 #endif
     void submit(void (*closure)())
     {
       work w ((closure));
       work_queue.push(boost::move(w));
       //work_queue.push(work(closure)); // todo check why this doesn't work
     }
 
     template <typename Closure>
     void submit(BOOST_THREAD_RV_REF(Closure) closure)
     {
       work w =boost::move(closure);
       work_queue.push(boost::move(w));
       //work_queue.push(work(boost::move(closure))); // todo check why this doesn't work
     }
 
     /**
      * \b Requires: This must be called from an scheduled task.
      *
      * \b Effects: reschedule functions until pred()
      */
     template <typename Pred>
     bool reschedule_until(Pred const& pred)
     {
       do {
         if ( ! try_executing_one())
         {
           return false;
         }
       } while (! pred());
       return true;
     }
     /**
      * run queued closures
      */
     void run_queued_closures()
     {
       sync_queue<work>::underlying_queue_type q = work_queue.underlying_queue();
       while (q.empty())
       {
         work task = q.front();
         q.pop_front();
         task();
       }
     }
 
   };
 
 }
 
 #include <boost/config/abi_suffix.hpp>
 
 #endif
 #endif

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