libstdc++
queue.h
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00001 // -*- C++ -*-
00002 
00003 // Copyright (C) 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the terms
00007 // of the GNU General Public License as published by the Free Software
00008 // Foundation; either version 3, or (at your option) any later
00009 // version.
00010 
00011 // This library is distributed in the hope that it will be useful, but
00012 // WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014 // General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file parallel/queue.h
00026  *  @brief Lock-free double-ended queue.
00027  *  This file is a GNU parallel extension to the Standard C++ Library.
00028  */
00029 
00030 // Written by Johannes Singler.
00031 
00032 #ifndef _GLIBCXX_PARALLEL_QUEUE_H
00033 #define _GLIBCXX_PARALLEL_QUEUE_H 1
00034 
00035 #include <parallel/types.h>
00036 #include <parallel/base.h>
00037 #include <parallel/compatibility.h>
00038 
00039 /** @brief Decide whether to declare certain variable volatile in this file. */
00040 #define _GLIBCXX_VOLATILE volatile
00041 
00042 namespace __gnu_parallel
00043 {
00044   /**@brief Double-ended queue of bounded size, allowing lock-free
00045    *  atomic access.  push_front() and pop_front() must not be called
00046    *  concurrently to each other, while pop_back() can be called
00047    *  concurrently at all times.
00048    *  @c empty(), @c size(), and @c top() are intentionally not provided.
00049    *  Calling them would not make sense in a concurrent setting.
00050    *  @param _Tp Contained element type. */
00051   template<typename _Tp>
00052     class _RestrictedBoundedConcurrentQueue
00053     {
00054     private:
00055       /** @brief Array of elements, seen as cyclic buffer. */
00056       _Tp* _M_base;
00057 
00058       /** @brief Maximal number of elements contained at the same time. */
00059       _SequenceIndex _M_max_size;
00060 
00061       /** @brief Cyclic __begin and __end pointers contained in one
00062           atomically changeable value. */
00063       _GLIBCXX_VOLATILE _CASable _M_borders;
00064 
00065     public:
00066       /** @brief Constructor. Not to be called concurrent, of course.
00067        *  @param __max_size Maximal number of elements to be contained. */
00068       _RestrictedBoundedConcurrentQueue(_SequenceIndex __max_size)
00069       {
00070         _M_max_size = __max_size;
00071         _M_base = new _Tp[__max_size];
00072         _M_borders = __encode2(0, 0);
00073 #pragma omp flush
00074       }
00075 
00076       /** @brief Destructor. Not to be called concurrent, of course. */
00077       ~_RestrictedBoundedConcurrentQueue()
00078       { delete[] _M_base; }
00079 
00080       /** @brief Pushes one element into the queue at the front end.
00081        *  Must not be called concurrently with pop_front(). */
00082       void
00083       push_front(const _Tp& __t)
00084       {
00085         _CASable __former_borders = _M_borders;
00086         int __former_front, __former_back;
00087         __decode2(__former_borders, __former_front, __former_back);
00088         *(_M_base + __former_front % _M_max_size) = __t;
00089 #if _GLIBCXX_ASSERTIONS
00090         // Otherwise: front - back > _M_max_size eventually.
00091         _GLIBCXX_PARALLEL_ASSERT(((__former_front + 1) - __former_back)
00092                                  <= _M_max_size);
00093 #endif
00094         __fetch_and_add(&_M_borders, __encode2(1, 0));
00095       }
00096 
00097       /** @brief Pops one element from the queue at the front end.
00098        *  Must not be called concurrently with pop_front(). */
00099       bool
00100       pop_front(_Tp& __t)
00101       {
00102         int __former_front, __former_back;
00103 #pragma omp flush
00104         __decode2(_M_borders, __former_front, __former_back);
00105         while (__former_front > __former_back)
00106           {
00107             // Chance.
00108             _CASable __former_borders = __encode2(__former_front,
00109                           __former_back);
00110             _CASable __new_borders = __encode2(__former_front - 1,
00111                            __former_back);
00112             if (__compare_and_swap(&_M_borders, __former_borders,
00113                    __new_borders))
00114               {
00115                 __t = *(_M_base + (__former_front - 1) % _M_max_size);
00116                 return true;
00117               }
00118 #pragma omp flush
00119             __decode2(_M_borders, __former_front, __former_back);
00120           }
00121         return false;
00122       }
00123 
00124       /** @brief Pops one element from the queue at the front end.
00125        *  Must not be called concurrently with pop_front(). */
00126       bool
00127       pop_back(_Tp& __t)        //queue behavior
00128       {
00129         int __former_front, __former_back;
00130 #pragma omp flush
00131         __decode2(_M_borders, __former_front, __former_back);
00132         while (__former_front > __former_back)
00133           {
00134             // Chance.
00135             _CASable __former_borders = __encode2(__former_front,
00136                           __former_back);
00137             _CASable __new_borders = __encode2(__former_front,
00138                            __former_back + 1);
00139             if (__compare_and_swap(&_M_borders, __former_borders,
00140                    __new_borders))
00141               {
00142                 __t = *(_M_base + __former_back % _M_max_size);
00143                 return true;
00144               }
00145 #pragma omp flush
00146             __decode2(_M_borders, __former_front, __former_back);
00147           }
00148         return false;
00149       }
00150   };
00151 }       //namespace __gnu_parallel
00152 
00153 #undef _GLIBCXX_VOLATILE
00154 
00155 #endif /* _GLIBCXX_PARALLEL_QUEUE_H */