restart.cpp

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/* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
/*
 *  Main authors:
 *     Christian Schulte <schulte@gecode.org>
 *
 *  Copyright:
 *     Christian Schulte, 2009
 *
 *  Last modified:
 *     $Date: 2009-05-13 21:19:00 +0200 (Wed, 13 May 2009) $ by $Author: schulte $
 *     $Revision: 9092 $
 *
 *  This file is part of Gecode, the generic constraint
 *  development environment:
 *     http://www.gecode.org
 *
 *  Permission is hereby granted, free of charge, to any person obtaining
 *  a copy of this software and associated documentation files (the
 *  "Software"), to deal in the Software without restriction, including
 *  without limitation the rights to use, copy, modify, merge, publish,
 *  distribute, sublicense, and/or sell copies of the Software, and to
 *  permit persons to whom the Software is furnished to do so, subject to
 *  the following conditions:
 *
 *  The above copyright notice and this permission notice shall be
 *  included in all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 *  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 *  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */

#include <gecode/search/parallel/restart.hh>

namespace Gecode { namespace Search { namespace Parallel {

  Space*
  Restart::next(void) {
    // Invariant: the worker holds the wait mutex
    m_search.acquire();
    // Check whether root space is already failed
    if (root == NULL) {
      m_search.release();
      return NULL;
    }
    while (!solutions.empty()) {
      // No search needs to be done, try to take leftover solution
      Space* s = solutions.pop();
      if (best == NULL) {
        best = s->clone();
        reset_needed = true;
        m_search.release();
        return s;
      } else {
        s->constrain(*best);
        if (s->status() == SS_FAILED) {
          delete s;
        } else {
          delete best;
          best = s->clone();
          reset_needed = true;
          m_search.release();
          return s;
        }
      }
    }
    // We ignore stopped (it will be reported again if needed)
    has_stopped = false;
    // No more solutions?
    if (n_busy == 0) {
      m_search.release();
      return NULL;
    }
    if (reset_needed) {
      reset_needed = false;
      root->constrain(*best);
      // Leave lock
      m_search.release();
      // Grab wait lock for reset
      m_wait_reset.acquire();
      // Release workers for reset
      release(C_RESET);
      // Wait for reset cycle started
      e_reset_ack_start.wait();
      // Perform reset
      root = reset(root);
      // Block workers again to ensure invariant
      block();
      // Release reset lock
      m_wait_reset.release();
      // Wait for reset cycle stopped
      e_reset_ack_stop.wait();
      if (root == NULL)
        return NULL;
    } else {
      m_search.release();
    }

    // Okay, now search has to continue, make the guys work
    release(C_WORK);

    /*
     * Wait until a search related event has happened. It might be that
     * the event has already been signalled in the last run, but the
     * solution has been removed. So we have to try until there has
     * something new happened.
     */
    while (true) {
      e_search.wait();
      m_search.acquire();
      while (!solutions.empty()) {
        // Check solution
        Space* s = solutions.pop();
        if (best == NULL) {
          best = s->clone();
          reset_needed = true;
          m_search.release();
          // Make workers wait again
          block();
          return s;
        } else {
          s->constrain(*best);
          if (s->status() == SS_FAILED) {
            delete s;
          } else {
            delete best;
            best = s->clone();
            reset_needed = true;
            m_search.release();
            // Make workers wait again
            block();
            return s;
          }
        }
      }
      // No more solutions or stopped?
      if ((n_busy == 0) || has_stopped) {
        m_search.release();
        // Make workers wait again
        block();
        return NULL;
      }
      m_search.release();
    }
    GECODE_NEVER;
    return NULL;
  }

  Restart::~Restart(void) {
    delete best;
    delete root;
  }

}}}

// STATISTICS: search-parallel