libstdc++-v3/include/parallel/queue.h

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2007 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the terms
   7 // of the GNU General Public License as published by the Free Software
   8 // Foundation; either version 2, or (at your option) any later
   9 // version.
  10
  11 // This library is distributed in the hope that it will be useful, but
  12 // WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 // General Public License for more details.
  15
  16 // You should have received a copy of the GNU General Public License
  17 // along with this library; see the file COPYING.  If not, write to
  18 // the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
  19 // MA 02111-1307, USA.
  20
  21 // As a special exception, you may use this file as part of a free
  22 // software library without restriction.  Specifically, if other files
  23 // instantiate templates or use macros or inline functions from this
  24 // file, or you compile this file and link it with other files to
  25 // produce an executable, this file does not by itself cause the
  26 // resulting executable to be covered by the GNU General Public
  27 // License.  This exception does not however invalidate any other
  28 // reasons why the executable file might be covered by the GNU General
  29 // Public License.
  30
  31 /** @file parallel/queue.h
  32  *  @brief Lock-free double-ended queue.
  33  *  This file is a GNU parallel extension to the Standard C++ Library.
  34  */
  35
  36 // Written by Johannes Singler.
  37
  38 #ifndef _GLIBCXX_PARALLEL_QUEUE_H
  39 #define _GLIBCXX_PARALLEL_QUEUE_H 1
  40
  41 #include <parallel/types.h>
  42 #include <parallel/base.h>
  43 #include <parallel/compatibility.h>
  44
  45 /** @brief Decide whether to declare certain variable volatile in this file. */
  46 #define _GLIBCXX_VOLATILE volatile
  47
  48 namespace __gnu_parallel
  49 {
  50   /**@brief Double-ended queue of bounded size, allowing lock-free
  51    *  atomic access.  push_front() and pop_front() must not be called
  52    *  concurrently to each other, while pop_back() can be called
  53    *  concurrently at all times.
  54    *  @c empty(), @c size(), and @c top() are intentionally not provided.
  55    *  Calling them would not make sense in a concurrent setting.
  56    *  @param T Contained element type. */
  57   template<typename T>
  58   class RestrictedBoundedConcurrentQueue
  59   {
  60   private:
  61     /** @brief Array of elements, seen as cyclic buffer. */
  62     T* base;
  63
  64     /** @brief Maximal number of elements contained at the same time. */
  65     sequence_index_t max_size;
  66
  67     /** @brief Cyclic begin and end pointers contained in one
  68         atomically changeable value. */
  69     _GLIBCXX_VOLATILE lcas_t borders;
  70
  71   public:
  72     /** @brief Constructor. Not to be called concurrent, of course.
  73      *  @param max_size Maximal number of elements to be contained. */
  74     RestrictedBoundedConcurrentQueue(sequence_index_t max_size)
  75     {
  76       this->max_size = max_size;
  77       base = new T[max_size];
  78       borders = encode2(0, 0);
  79 #pragma omp flush
  80     }
  81
  82     /** @brief Destructor. Not to be called concurrent, of course. */
  83     ~RestrictedBoundedConcurrentQueue()
  84     {
  85       delete[] base;
  86     }
  87
  88     /** @brief Pushes one element into the queue at the front end.
  89      *  Must not be called concurrently with pop_front(). */
  90     void push_front(const T& t)
  91     {
  92       lcas_t former_borders = borders;
  93       int former_front, former_back;
  94       decode2(former_borders, former_front, former_back);
  95       *(base + former_front % max_size) = t;
  96 #if _GLIBCXX_ASSERTIONS
  97       // Otherwise: front - back > max_size eventually.
  98       _GLIBCXX_PARALLEL_ASSERT(((former_front + 1) - former_back) <= max_size);
  99 #endif
 100       fetch_and_add(&borders, encode2(1, 0));
 101     }
 102
 103     /** @brief Pops one element from the queue at the front end.
 104      *  Must not be called concurrently with pop_front(). */
 105     bool pop_front(T& t)
 106     {
 107       int former_front, former_back;
 108 #pragma omp flush
 109       decode2(borders, former_front, former_back);
 110       while (former_front > former_back)
 111         {
 112           // Chance.
 113           lcas_t former_borders = encode2(former_front, former_back);
 114           lcas_t new_borders = encode2(former_front - 1, former_back);
 115           if (compare_and_swap(&borders, former_borders, new_borders))
 116             {
 117               t = *(base + (former_front - 1) % max_size);
 118               return true;
 119             }
 120 #pragma omp flush
 121           decode2(borders, former_front, former_back);
 122         }
 123       return false;
 124     }
 125
 126     /** @brief Pops one element from the queue at the front end.
 127      *  Must not be called concurrently with pop_front(). */
 128     bool pop_back(T& t) //queue behavior
 129     {
 130       int former_front, former_back;
 131 #pragma omp flush
 132       decode2(borders, former_front, former_back);
 133       while (former_front > former_back)
 134         {
 135           // Chance.
 136           lcas_t former_borders = encode2(former_front, former_back);
 137           lcas_t new_borders = encode2(former_front, former_back + 1);
 138           if (compare_and_swap(&borders, former_borders, new_borders))
 139             {
 140               t = *(base + former_back % max_size);
 141               return true;
 142             }
 143 #pragma omp flush
 144           decode2(borders, former_front, former_back);
 145         }
 146       return false;
 147     }
 148   };
 149 }       //namespace __gnu_parallel
 150
 151 #undef _GLIBCXX_VOLATILE
 152
 153 #endif