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/noncopyable.hpp>
  27
  28 namespace caspar {
  29
  30 /**
  31  * Adapts an unbounded non-blocking concurrent queue into a blocking bounded
  32  * concurrent queue.
  33  *
  34  * The queue Q to adapt must support the following use cases:
  35  *
  36  * Q q;
  37  * Q::value_type elem;
  38  * q.push(elem);
  39  *
  40  * and:
  41  *
  42  * Q q;
  43  * Q::value_type elem;
  44  * q.try_pop(elem);
  45  *
  46  * It must also guarantee thread safety for those operations.
  47  */
  48 template<class Q>
  49 class blocking_bounded_queue_adapter : boost::noncopyable
  50 {
  51 public:
  52         typedef typename Q::value_type value_type;
  53         typedef unsigned int size_type;
  54 private:
  55         mutable std::mutex      capacity_mutex_;
  56         size_type                               capacity_;
  57         semaphore                               space_available_                = capacity_;
  58         semaphore                               elements_available_             = 0;
  59         Q                                               queue_;
  60 public:
  61         /**
  62          * Constructor.
  63          *
  64          * @param capacity The capacity of the queue.
  65          */
  66         blocking_bounded_queue_adapter(size_type capacity)
  67                 : capacity_(capacity)
  68         {
  69         }
  70
  71         /**
  72          * Push an element to the queue, block until room is available.
  73          *
  74          * @param element The element to push.
  75          */
  76         void push(const value_type& element)
  77         {
  78                 space_available_.acquire();
  79                 push_after_room_reserved(element);
  80         }
  81
  82         /**
  83          * Try to push an element to the queue, returning immediately if room is not
  84          * available.
  85          *
  86          * @param element The element to push.
  87          *
  88          * @return true if there was room for the element.
  89          */
  90         bool try_push(const value_type& element)
  91         {
  92                 bool room_available = space_available_.try_acquire();
  93
  94                 if (!room_available)
  95                         return false;
  96
  97                 push_after_room_reserved(element);
  98
  99                 return true;
 100         }
 101
 102         /**
 103          * Pop an element from the queue, will block until an element is available.
 104          *
 105          * @param element The element to store the result in.
 106          */
 107         void pop(value_type& element)
 108         {
 109                 elements_available_.acquire();
 110                 queue_.try_pop(element);
 111                 space_available_.release();
 112         }
 113
 114         /**
 115          * Try to pop an element from the queue, returning immediately if no
 116          * element is available.
 117          *
 118          * @param element The element to store the result in.
 119          *
 120          * @return true if an element was popped.
 121          */
 122         bool try_pop(value_type& element)
 123         {
 124                 if (!elements_available_.try_acquire())
 125                         return false;
 126
 127                 queue_.try_pop(element);
 128                 space_available_.release();
 129
 130                 return true;
 131         }
 132
 133         /**
 134          * Modify the capacity of the queue. May block if reducing the capacity.
 135          *
 136          * @param capacity The new capacity.
 137          */
 138         void set_capacity(size_type capacity)
 139         {
 140                 std::unique_lock<std::mutex> lock (capacity_mutex_);
 141
 142                 if (capacity_ < capacity)
 143                 {
 144                         auto to_grow_with = capacity - capacity_;
 145
 146                         space_available_.release(to_grow_with);
 147                 }
 148                 else if (capacity_ > capacity)
 149                 {
 150                         auto to_shrink_with = capacity_ - capacity;
 151
 152                         // Will block until the desired capacity has been reached.
 153                         space_available_.acquire(to_shrink_with);
 154                 }
 155
 156                 capacity_ = capacity;
 157         }
 158
 159         /**
 160          * @return the current capacity of the queue.
 161          */
 162         size_type capacity() const
 163         {
 164                 std::unique_lock<std::mutex> lock (capacity_mutex_);
 165
 166                 return capacity_;
 167         }
 168
 169         /**
 170          * @return the current size of the queue (may have changed at the time of
 171          *         returning).
 172          */
 173         size_type size() const
 174         {
 175                 return elements_available_.permits();
 176         }
 177 private:
 178         void push_after_room_reserved(const value_type& element)
 179         {
 180                 try
 181                 {
 182                         queue_.push(element);
 183                 }
 184                 catch (...)
 185                 {
 186                         space_available_.release();
 187
 188                         throw;
 189                 }
 190
 191                 elements_available_.release();
 192         }
 193 };
 194
 195 }