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         mutable boost::mutex    capacity_mutex_;
  57         size_type                               capacity_;
  58         semaphore                               space_available_                = capacity_;
  59         semaphore                               elements_available_             = 0;
  60         Q                                               queue_;
  61 public:
  62         /**
  63          * Constructor.
  64          *
  65          * @param capacity The capacity of the queue.
  66          */
  67         blocking_bounded_queue_adapter(size_type capacity)
  68                 : capacity_(capacity)
  69         {
  70         }
  71
  72         /**
  73          * Push an element to the queue, block until room is available.
  74          *
  75          * @param element The element to push.
  76          */
  77         void push(const value_type& element)
  78         {
  79                 space_available_.acquire();
  80                 push_after_room_reserved(element);
  81         }
  82
  83         /**
  84          * Try to push an element to the queue, returning immediately if room is not
  85          * available.
  86          *
  87          * @param element The element to push.
  88          *
  89          * @return true if there was room for the element.
  90          */
  91         bool try_push(const value_type& element)
  92         {
  93                 bool room_available = space_available_.try_acquire();
  94
  95                 if (!room_available)
  96                         return false;
  97
  98                 push_after_room_reserved(element);
  99
 100                 return true;
 101         }
 102
 103         /**
 104          * Pop an element from the queue, will block until an element is available.
 105          *
 106          * @param element The element to store the result in.
 107          */
 108         void pop(value_type& element)
 109         {
 110                 elements_available_.acquire();
 111                 queue_.try_pop(element);
 112                 space_available_.release();
 113         }
 114
 115         /**
 116          * Try to pop an element from the queue, returning immediately if no
 117          * element is available.
 118          *
 119          * @param element The element to store the result in.
 120          *
 121          * @return true if an element was popped.
 122          */
 123         bool try_pop(value_type& element)
 124         {
 125                 if (!elements_available_.try_acquire())
 126                         return false;
 127
 128                 queue_.try_pop(element);
 129                 space_available_.release();
 130
 131                 return true;
 132         }
 133
 134         /**
 135          * Modify the capacity of the queue. May block if reducing the capacity.
 136          *
 137          * @param capacity The new capacity.
 138          */
 139         void set_capacity(size_type capacity)
 140         {
 141                 boost::unique_lock<boost::mutex> lock (capacity_mutex_);
 142
 143                 if (capacity_ < capacity)
 144                 {
 145                         auto to_grow_with = capacity - capacity_;
 146
 147                         space_available_.release(to_grow_with);
 148                 }
 149                 else if (capacity_ > capacity)
 150                 {
 151                         auto to_shrink_with = capacity_ - capacity;
 152
 153                         // Will block until the desired capacity has been reached.
 154                         space_available_.acquire(to_shrink_with);
 155                 }
 156
 157                 capacity_ = capacity;
 158         }
 159
 160         /**
 161          * @return the current capacity of the queue.
 162          */
 163         size_type capacity() const
 164         {
 165                 boost::unique_lock<boost::mutex> lock (capacity_mutex_);
 166
 167                 return capacity_;
 168         }
 169
 170         /**
 171          * @return the current size of the queue (may have changed at the time of
 172          *         returning).
 173          */
 174         size_type size() const
 175         {
 176                 return elements_available_.permits();
 177         }
 178 private:
 179         void push_after_room_reserved(const value_type& element)
 180         {
 181                 try
 182                 {
 183                         queue_.push(element);
 184                 }
 185                 catch (...)
 186                 {
 187                         space_available_.release();
 188
 189                         throw;
 190                 }
 191
 192                 elements_available_.release();
 193         }
 194 };
 195
 196 }