git.sesse.net Git - casparcg/blob - common/blocking_priority_queue.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 #pragma once
  22
  23 #include <stdexcept>
  24 #include <map>
  25 #include <initializer_list>
  26
  27 #include <tbb/concurrent_queue.h>
  28
  29 #include <boost/foreach.hpp>
  30 #include <boost/thread/mutex.hpp>
  31
  32 #include "semaphore.h"
  33
  34 namespace caspar {
  35
  36 /**
  37  * Blocking concurrent priority queue supporting a predefined set of
  38  * priorities. FIFO ordering is guaranteed within a priority.
  39  *
  40  * Prio must have the < and > operators defined where a larger instance is of a
  41  * higher priority.
  42  */
  43 template <class T, class Prio>
  44 class blocking_priority_queue
  45 {
  46 public:
  47         typedef unsigned int size_type;
  48 private:
  49         std::map<Prio, tbb::concurrent_queue<T>, std::greater<Prio>> queues_by_priority_;
  50         semaphore space_available_;
  51         semaphore elements_available_;
  52         mutable boost::mutex capacity_mutex_;
  53         size_type capacity_;
  54 public:
  55         /**
  56          * Constructor.
  57          *
  58          * @param capacity   The initial capacity of the queue.
  59          * @param priorities A forward iterable container with the priorities to
  60          *                   support.
  61          */
  62         template<class PrioList>
  63         blocking_priority_queue(size_type capacity, const PrioList& priorities)
  64                 : space_available_(capacity)
  65                 , elements_available_(0u)
  66                 , capacity_(capacity)
  67         {
  68                 BOOST_FOREACH(Prio priority, priorities)
  69                 {
  70                         queues_by_priority_.insert(std::make_pair(priority, tbb::concurrent_queue<T>()));
  71                 }
  72
  73                 // The std::map is read-only from now on, so there *should* (it is
  74                 // unlikely but possible for a std::map implementor to choose to
  75                 // rebalance the tree during read operations) be no race conditions
  76                 // regarding the map.
  77                 //
  78                 // This may be true for vc10 as well:
  79                 // http://msdn.microsoft.com/en-us/library/c9ceah3b%28VS.80%29.aspx
  80         }
  81
  82         /**
  83          * Push an element with a given priority to the queue. Blocks until room
  84          * is available.
  85          *
  86          * @param priority The priority of the element.
  87          * @param element  The element.
  88          */
  89         void push(Prio priority, const T& element)
  90         {
  91                 acquire_transaction transaction(space_available_);
  92
  93                 push_acquired(priority, element, transaction);
  94         }
  95
  96         /**
  97          * Attempt to push an element with a given priority to the queue. Will
  98          * immediately return even if there is no room in the queue.
  99          *
 100          * @param priority The priority of the element.
 101          * @param element  The element.
 102          *
 103          * @return true if the element was pushed. false if there was no room.
 104          */
 105         bool try_push(Prio priority, const T& element)
 106         {
 107                 if (!space_available_.try_acquire())
 108                         return false;
 109
 110                 acquire_transaction transaction(space_available_, true);
 111
 112                 push_acquired(priority, element, transaction);
 113
 114                 return true;
 115         }
 116
 117         /**
 118          * Pop the element with the highest priority (fifo for elements with the
 119          * same priority). Blocks until an element is available.
 120          *
 121          * @param element The element to store the result in.
 122          */
 123         void pop(T& element)
 124         {
 125                 acquire_transaction transaction(elements_available_);
 126
 127                 pop_acquired_any_priority(element, transaction);
 128         }
 129
 130         /**
 131          * Attempt to pop the element with the highest priority (fifo for elements
 132          * with the same priority) if available. Does not wait until an element is
 133          * available.
 134          *
 135          * @param element The element to store the result in.
 136          *
 137          * @return true if an element was available.
 138          */
 139         bool try_pop(T& element)
 140         {
 141                 if (!elements_available_.try_acquire())
 142                         return false;
 143
 144                 acquire_transaction transaction(elements_available_, true);
 145
 146                 pop_acquired_any_priority(element, transaction);
 147
 148                 return true;
 149         }
 150
 151         /**
 152          * Attempt to pop the element with the highest priority (fifo for elements
 153          * with the same priority) if available *and* has a minimum priority. Does
 154          * not wait until an element satisfying the priority criteria is available.
 155          *
 156          * @param element          The element to store the result in.
 157          * @param minimum_priority The minimum priority to accept.
 158          *
 159          * @return true if an element was available with the minimum priority.
 160          */
 161         bool try_pop(T& element, Prio minimum_priority)
 162         {
 163                 if (!elements_available_.try_acquire())
 164                         return false;
 165
 166                 acquire_transaction transaction(elements_available_, true);
 167
 168                 BOOST_FOREACH(auto& queue, queues_by_priority_)
 169                 {
 170                         if (queue.first < minimum_priority)
 171                         {
 172                                 // Will be true for all queues from this point so we break.
 173                                 break;
 174                         }
 175
 176                         if (queue.second.try_pop(element))
 177                         {
 178                                 transaction.commit();
 179                                 space_available_.release();
 180
 181                                 return true;
 182                         }
 183                 }
 184
 185                 return false;
 186         }
 187
 188         /**
 189          * Modify the capacity of the queue. May block if reducing the capacity.
 190          *
 191          * @param capacity The new capacity.
 192          */
 193         void set_capacity(size_type capacity)
 194         {
 195                 boost::mutex::scoped_lock lock (capacity_mutex_);
 196
 197                 if (capacity_ < capacity)
 198                 {
 199                         auto to_grow_with = capacity - capacity_;
 200                         space_available_.release(to_grow_with);
 201                 }
 202                 else if (capacity_ > capacity)
 203                 {
 204                         auto to_shrink_with = capacity_ - capacity;
 205                         // Will block until the desired capacity has been reached.
 206                         space_available_.acquire(to_shrink_with);
 207                 }
 208
 209                 capacity_ = capacity;
 210         }
 211
 212         /**
 213          * @return the current capacity of the queue.
 214          */
 215         size_type capacity() const
 216         {
 217                 boost::mutex::scoped_lock lock (capacity_mutex_);
 218
 219                 return capacity_;
 220         }
 221
 222         /**
 223          * @return the current size of the queue (may have changed at the time of
 224          *         returning).
 225          */
 226         size_type size() const
 227         {
 228                 return elements_available_.permits();
 229         }
 230 private:
 231         void push_acquired(Prio priority, const T& element, acquire_transaction& transaction)
 232         {
 233                 try
 234                 {
 235                         queues_by_priority_.at(priority).push(element);
 236                 }
 237                 catch (std::out_of_range&)
 238                 {
 239                         throw std::runtime_error("Priority not supported by queue");
 240                 }
 241
 242                 transaction.commit();
 243                 elements_available_.release();
 244         }
 245
 246         void pop_acquired_any_priority(T& element, acquire_transaction& transaction)
 247         {
 248                 BOOST_FOREACH(auto& queue, queues_by_priority_)
 249                 {
 250                         if (queue.second.try_pop(element))
 251                         {
 252                                 transaction.commit();
 253                                 space_available_.release();
 254
 255                                 return;
 256                         }
 257                 }
 258
 259                 throw std::logic_error(
 260                                 "blocking_priority_queue should have contained at least one element but didn't");
 261         }
 262 };
 263
 264 }