git.sesse.net Git - casparcg/blob - common/blocking_bounded_queue_adapter.h

   1 /*
   2 * Copyright (c) 2011 Sveriges Television AB <info@casparcg.com>
   3 *
   4 * This file is part of CasparCG (www.casparcg.com).
   5 *
   6 * CasparCG is free software: you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License as published by
   8 * the Free Software Foundation, either version 3 of the License, or
   9 * (at your option) any later version.
  10 *
  11 * CasparCG is distributed in the hope that it will be useful,
  12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 * GNU General Public License for more details.
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * along with CasparCG. If not, see <http://www.gnu.org/licenses/>.
  18 *
  19 * Author: Helge Norberg, helge.norberg@svt.se
  20 */
  21
  22 #pragma once
  23
  24 #include "semaphore.h"
  25
  26 #include <boost/thread/mutex.hpp>
  27 #include <boost/noncopyable.hpp>
  28
  29 namespace caspar {
  30
  31 /**
  32  * Adapts an unbounded non-blocking concurrent queue into a blocking bounded
  33  * concurrent queue.
  34  *
  35  * The queue Q to adapt must support the following use cases:
  36  *
  37  * Q q;
  38  * Q::value_type elem;
  39  * q.push(elem);
  40  *
  41  * and:
  42  *
  43  * Q q;
  44  * Q::value_type elem;
  45  * q.try_pop(elem);
  46  *
  47  * It must also guarantee thread safety for those operations.
  48  */
  49 template<class Q>
  50 class blocking_bounded_queue_adapter : boost::noncopyable
  51 {
  52 public:
  53         typedef typename Q::value_type value_type;
  54         typedef unsigned int size_type;
  55 private:
  56         semaphore space_available_;
  57         semaphore elements_available_;
  58         Q queue_;
  59         mutable boost::mutex capacity_mutex_;
  60         size_type capacity_;
  61 public:
  62         /**
  63          * Constructor.
  64          *
  65          * @param capacity The capacity of the queue.
  66          */
  67         blocking_bounded_queue_adapter(size_type capacity)
  68                 : space_available_(capacity)
  69                 , elements_available_(0)
  70                 , capacity_(capacity)
  71         {
  72         }
  73
  74         /**
  75          * Push an element to the queue, block until room is available.
  76          *
  77          * @param element The element to push.
  78          */
  79         void push(const value_type& element)
  80         {
  81                 space_available_.acquire();
  82                 push_after_room_reserved(element);
  83         }
  84
  85         /**
  86          * Try to push an element to the queue, returning immediately if room is not
  87          * available.
  88          *
  89          * @param element The element to push.
  90          *
  91          * @return true if there was room for the element.
  92          */
  93         bool try_push(const value_type& element)
  94         {
  95                 bool room_available = space_available_.try_acquire();
  96
  97                 if (!room_available)
  98                         return false;
  99
 100                 push_after_room_reserved(element);
 101
 102                 return true;
 103         }
 104
 105         /**
 106          * Pop an element from the queue, will block until an element is available.
 107          *
 108          * @param element The element to store the result in.
 109          */
 110         void pop(value_type& element)
 111         {
 112                 elements_available_.acquire();
 113                 queue_.try_pop(element);
 114                 space_available_.release();
 115         }
 116
 117         /**
 118          * Try to pop an element from the queue, returning immediately if no
 119          * element is available.
 120          *
 121          * @param element The element to store the result in.
 122          *
 123          * @return true if an element was popped.
 124          */
 125         bool try_pop(value_type& element)
 126         {
 127                 if (!elements_available_.try_acquire())
 128                         return false;
 129
 130                 queue_.try_pop(element);
 131                 space_available_.release();
 132
 133                 return true;
 134         }
 135
 136         /**
 137          * Modify the capacity of the queue. May block if reducing the capacity.
 138          *
 139          * @param capacity The new capacity.
 140          */
 141         void set_capacity(size_type capacity)
 142         {
 143                 boost::mutex::scoped_lock lock (capacity_mutex_);
 144
 145                 if (capacity_ < capacity)
 146                 {
 147                         auto to_grow_with = capacity - capacity_;
 148
 149                         space_available_.release(to_grow_with);
 150                 }
 151                 else if (capacity_ > capacity)
 152                 {
 153                         auto to_shrink_with = capacity_ - capacity;
 154
 155                         // Will block until the desired capacity has been reached.
 156                         space_available_.acquire(to_shrink_with);
 157                 }
 158
 159                 capacity_ = capacity;
 160         }
 161
 162         /**
 163          * @return the current capacity of the queue.
 164          */
 165         size_type capacity() const
 166         {
 167                 boost::mutex::scoped_lock lock (capacity_mutex_);
 168
 169                 return capacity_;
 170         }
 171
 172         /**
 173          * @return the current size of the queue (may have changed at the time of
 174          *         returning).
 175          */
 176         size_type size() const
 177         {
 178                 return elements_available_.permits();
 179         }
 180 private:
 181         void push_after_room_reserved(const value_type& element)
 182         {
 183                 try
 184                 {
 185                         queue_.push(element);
 186                 }
 187                 catch (...)
 188                 {
 189                         space_available_.release();
 190
 191                         throw;
 192                 }
 193
 194                 elements_available_.release();
 195         }
 196 };
 197
 198 }