src/base/barrier.hh

   1 /*
   2  * Copyright (c) 2013 ARM Limited
   3  * All rights reserved
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   9  * licensed hereunder.  You may use the software subject to the license
  10  * terms below provided that you ensure that this notice is replicated
  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Redistribution and use in source and binary forms, with or without
  15  * modification, are permitted provided that the following conditions are
  16  * met: redistributions of source code must retain the above copyright
  17  * notice, this list of conditions and the following disclaimer;
  18  * redistributions in binary form must reproduce the above copyright
  19  * notice, this list of conditions and the following disclaimer in the
  20  * documentation and/or other materials provided with the distribution;
  21  * neither the name of the copyright holders nor the names of its
  22  * contributors may be used to endorse or promote products derived from
  23  * this software without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  26  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  27  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  28  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  29  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  30  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  31  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  32  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  33  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  35  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  *
  37  * Authors: Ali Saidi
  38  */
  39
  40 #ifndef __BASE_BARRIER_HH__
  41 #define __BASE_BARRIER_HH__
  42
  43 #include <condition_variable>
  44
  45 class Barrier
  46 {
  47   private:
  48     /// Mutex to protect access to numLeft and generation
  49     std::mutex bMutex;
  50     /// Condition variable for waiting on barrier
  51     std::condition_variable bCond;
  52     /// Number of threads we should be waiting for before completing the barrier
  53     unsigned numWaiting;
  54     /// Generation of this barrier
  55     unsigned generation;
  56     /// Number of threads remaining for the current generation
  57     unsigned numLeft;
  58
  59   public:
  60     Barrier(unsigned _numWaiting)
  61         : numWaiting(_numWaiting), generation(0), numLeft(_numWaiting)
  62     {}
  63
  64     bool
  65     wait()
  66     {
  67         std::unique_lock<std::mutex> lock(bMutex);
  68         unsigned int gen = generation;
  69
  70         if (--numLeft == 0) {
  71             generation++;
  72             numLeft = numWaiting;
  73             bCond.notify_all();
  74             return true;
  75         }
  76         while (gen == generation)
  77             bCond.wait(lock);
  78         return false;
  79     }
  80 };
  81
  82 #endif // __BASE_BARRIER_HH__