Barrier.h

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/*
 * This file belongs to the Galois project, a C++ library for exploiting
 * parallelism. The code is being released under the terms of the 3-Clause BSD
 * License (a copy is located in LICENSE.txt at the top-level directory).
 *
 * Copyright (C) 2018, The University of Texas at Austin. All rights reserved.
 * UNIVERSITY EXPRESSLY DISCLAIMS ANY AND ALL WARRANTIES CONCERNING THIS
 * SOFTWARE AND DOCUMENTATION, INCLUDING ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR ANY PARTICULAR PURPOSE, NON-INFRINGEMENT AND WARRANTIES OF
 * PERFORMANCE, AND ANY WARRANTY THAT MIGHT OTHERWISE ARISE FROM COURSE OF
 * DEALING OR USAGE OF TRADE.  NO WARRANTY IS EITHER EXPRESS OR IMPLIED WITH
 * RESPECT TO THE USE OF THE SOFTWARE OR DOCUMENTATION. Under no circumstances
 * shall University be liable for incidental, special, indirect, direct or
 * consequential damages or loss of profits, interruption of business, or
 * related expenses which may arise from use of Software or Documentation,
 * including but not limited to those resulting from defects in Software and/or
 * Documentation, or loss or inaccuracy of data of any kind.
 */

#ifndef GALOIS_SUBSTRATE_BARRIER_H
#define GALOIS_SUBSTRATE_BARRIER_H

#include <functional>
#include <memory>

#include "galois/config.h"
#include "galois/gIO.h"
#include "galois/substrate/ThreadPool.h"

namespace galois {
namespace substrate {

class Barrier {
public:
  virtual ~Barrier();

  // not safe if any thread is in wait
  virtual void reinit(unsigned val) = 0;

  // Wait at this barrier
  virtual void wait() = 0;

  // wait at this barrier
  void operator()(void) { wait(); }

  // barrier type.
  virtual const char* name() const = 0;
};

Barrier& getBarrier(unsigned activeThreads);

std::unique_ptr<Barrier> createPthreadBarrier(unsigned);
std::unique_ptr<Barrier> createMCSBarrier(unsigned);
std::unique_ptr<Barrier> createTopoBarrier(unsigned);
std::unique_ptr<Barrier> createCountingBarrier(unsigned);
std::unique_ptr<Barrier> createDisseminationBarrier(unsigned);

std::unique_ptr<Barrier> createSimpleBarrier(unsigned int);

namespace internal {

template <typename _UNUSED = void>
struct BarrierInstance {
  unsigned m_num_threads;
  std::unique_ptr<Barrier> m_barrier;

  BarrierInstance(void) {
    m_num_threads = getThreadPool().getMaxThreads();
    m_barrier     = createTopoBarrier(m_num_threads);
  }

  Barrier& get(unsigned numT) {
    GALOIS_ASSERT(numT > 0,
                  "substrate::getBarrier() number of threads must be > 0");

    numT = std::min(numT, getThreadPool().getMaxUsableThreads());
    numT = std::max(numT, 1u);

    if (numT != m_num_threads) {
      m_num_threads = numT;
      m_barrier->reinit(numT);
    }

    return *m_barrier;
  }
};

void setBarrierInstance(BarrierInstance<>* bi);

} // end namespace internal

} // end namespace substrate
} // end namespace galois

#endif