barrier.hh

Go to the documentation of this file.

// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
 
// SPDX-FileCopyrightText: Copyright © DUNE-FUFEM Project contributors, see file AUTHORS.md
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception OR LGPL-3.0-or-later
 
#ifndef DUNE_FUFEM_PARALLEL_BARRIER_HH
#define DUNE_FUFEM_PARALLEL_BARRIER_HH
 
#include <cstddef>
#include <mutex>
#include <condition_variable>
 
 
 
namespace Dune {
namespace Fufem {
 
 
class Barrier {
public:
 
  Barrier(std::size_t count):
    safedCount_(count), remaining_(count), phase_(0)
  {}
 
  void arrive_and_wait()
  {
    // Acquire lock for writing to shared counter remaining_.
    auto l = std::unique_lock(mut);
    --remaining_;
    if (remaining_ != 0)
    {
      // If we're not the last thread to arrive:
      // Wait until all thread have been notified by the last one.
      // To avoid lost or spurious wake-ups one should always use
      // a condition.
      auto myphase = phase_+1;
      cv.wait(l, [&]{ return myphase <= phase_; });
    }
    else
    {
      // If we're the last thread to arrive:
      // Reset counter, proceed to next phase to provide a checkable condition
      // for the other threads and notify them that we're done.
      remaining_ = safedCount_;
      ++phase_;
      cv.notify_all();
    }
  }
 
private:
  mutable std::mutex mut;
  std::condition_variable cv;
  std::size_t safedCount_;
  std::ptrdiff_t remaining_;
  std::ptrdiff_t phase_ = 0;
};
 
 
 
} // namespace Fufem
} // namespace Dune
 
 
#endif // DUNE_FUFEM_PARALLEL_BARRIER_HH