boost/statechart/fifo_worker.hpp

   1 #ifndef BOOST_STATECHART_FIFO_WORKER_HPP_INCLUDED
   2 #define BOOST_STATECHART_FIFO_WORKER_HPP_INCLUDED
   3 //////////////////////////////////////////////////////////////////////////////
   4 // Copyright 2002-2008 Andreas Huber Doenni
   5 // Distributed under the Boost Software License, Version 1.0. (See accompany-
   6 // ing file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7 //////////////////////////////////////////////////////////////////////////////
   8
   9
  10
  11 #include <boost/assert.hpp>
  12 #include <boost/noncopyable.hpp>
  13 #include <boost/function/function0.hpp>
  14 #include <boost/bind.hpp>
  15 // BOOST_HAS_THREADS, BOOST_MSVC
  16 #include <boost/config.hpp>
  17
  18 #include <boost/detail/allocator_utilities.hpp>
  19
  20 #ifdef BOOST_HAS_THREADS
  21 #  ifdef BOOST_MSVC
  22 #    pragma warning( push )
  23      // "conditional expression is constant" in basic_timed_mutex.hpp
  24 #    pragma warning( disable: 4127 )
  25      // "conversion from 'int' to 'unsigned short'" in microsec_time_clock.hpp
  26 #    pragma warning( disable: 4244 )
  27      // "... needs to have dll-interface to be used by clients of class ..."
  28 #    pragma warning( disable: 4251 )
  29      // "... assignment operator could not be generated"
  30 #    pragma warning( disable: 4512 )
  31      // "Function call with parameters that may be unsafe" in
  32      // condition_variable.hpp
  33 #    pragma warning( disable: 4996 )
  34 #  endif
  35
  36 #  include <boost/thread/mutex.hpp>
  37 #  include <boost/thread/condition.hpp>
  38
  39 #  ifdef BOOST_MSVC
  40 #    pragma warning( pop )
  41 #  endif
  42 #endif
  43
  44 #include <list>
  45 #include <memory>   // std::allocator
  46
  47
  48 namespace boost
  49 {
  50 namespace statechart
  51 {
  52
  53
  54
  55 template< class Allocator = std::allocator< void > >
  56 class fifo_worker : noncopyable
  57 {
  58   public:
  59     //////////////////////////////////////////////////////////////////////////
  60     #ifdef BOOST_HAS_THREADS
  61     fifo_worker( bool waitOnEmptyQueue = false ) :
  62       waitOnEmptyQueue_( waitOnEmptyQueue ),
  63     #else
  64     fifo_worker() :
  65     #endif
  66       terminated_( false )
  67     {
  68     }
  69
  70     typedef function0< void > work_item;
  71
  72     // We take a non-const reference so that we can move (i.e. swap) the item
  73     // into the queue, what avoids copying the (possibly heap-allocated)
  74     // implementation object inside work_item.
  75     void queue_work_item( work_item & item )
  76     {
  77       if ( item.empty() )
  78       {
  79         return;
  80       }
  81
  82       #ifdef BOOST_HAS_THREADS
  83       mutex::scoped_lock lock( mutex_ );
  84       #endif
  85
  86       workQueue_.push_back( work_item() );
  87       workQueue_.back().swap( item );
  88
  89       #ifdef BOOST_HAS_THREADS
  90       queueNotEmpty_.notify_one();
  91       #endif
  92     }
  93
  94     // Convenience overload so that temporary objects can be passed directly
  95     // instead of having to create a work_item object first. Under most
  96     // circumstances, this will lead to one unnecessary copy of the
  97     // function implementation object.
  98     void queue_work_item( const work_item & item )
  99     {
 100       work_item copy = item;
 101       queue_work_item( copy );
 102     }
 103
 104     void terminate()
 105     {
 106       work_item item = bind( &fifo_worker::terminate_impl, this );
 107       queue_work_item( item );
 108     }
 109
 110     // Is not mutex-protected! Must only be called from the thread that also
 111     // calls operator().
 112     bool terminated() const
 113     {
 114       return terminated_;
 115     }
 116
 117     unsigned long operator()( unsigned long maxItemCount = 0 )
 118     {
 119       unsigned long itemCount = 0;
 120
 121       while ( !terminated() &&
 122         ( ( maxItemCount == 0 ) || ( itemCount < maxItemCount ) ) )
 123       {
 124         work_item item = dequeue_item();
 125
 126         if ( item.empty() )
 127         {
 128           // item can only be empty when the queue is empty, which only
 129           // happens in ST builds or when users pass false to the fifo_worker
 130           // constructor
 131           return itemCount;
 132         }
 133
 134         item();
 135         ++itemCount;
 136       }
 137
 138       return itemCount;
 139     }
 140
 141   private:
 142     //////////////////////////////////////////////////////////////////////////
 143     work_item dequeue_item()
 144     {
 145       #ifdef BOOST_HAS_THREADS
 146       mutex::scoped_lock lock( mutex_ );
 147
 148       if ( !waitOnEmptyQueue_ && workQueue_.empty() )
 149       {
 150         return work_item();
 151       }
 152
 153       while ( workQueue_.empty() )
 154       {
 155         queueNotEmpty_.wait( lock );
 156       }
 157       #else
 158       // If the queue happens to run empty in a single-threaded system,
 159       // waiting for new work items (which means to loop indefinitely!) is
 160       // pointless as there is no way that new work items could find their way
 161       // into the queue. The only sensible thing is to exit the loop and
 162       // return to the caller in this case.
 163       // Users can then queue new work items before calling operator() again.
 164       if ( workQueue_.empty() )
 165       {
 166         return work_item();
 167       }
 168       #endif
 169
 170       // Optimization: Swap rather than assign to avoid the copy of the
 171       // implementation object inside function
 172       work_item result;
 173       result.swap( workQueue_.front() );
 174       workQueue_.pop_front();
 175       return result;
 176     }
 177
 178     void terminate_impl()
 179     {
 180       terminated_ = true;
 181     }
 182
 183
 184     typedef std::list<
 185       work_item,
 186       typename boost::detail::allocator::rebind_to<
 187         Allocator, work_item >::type
 188     > work_queue_type;
 189
 190     work_queue_type workQueue_;
 191
 192     #ifdef BOOST_HAS_THREADS
 193     mutex mutex_;
 194     condition queueNotEmpty_;
 195     const bool waitOnEmptyQueue_;
 196     #endif
 197
 198     bool terminated_;
 199 };
 200
 201
 202
 203 } // namespace statechart
 204 } // namespace boost
 205
 206
 207
 208 #endif