path.hh

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/* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
/*
 *  Main authors:
 *     Christian Schulte <schulte@gecode.org>
 *
 *  Copyright:
 *     Christian Schulte, 2003
 *
 *  Last modified:
 *     $Date: 2013-02-26 10:47:43 +0100 (Tue, 26 Feb 2013) $ by $Author: schulte $
 *     $Revision: 13414 $
 *
 *  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
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 *
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 *  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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 */

#ifndef __GECODE_SEARCH_PARALLEL_PATH_HH__
#define __GECODE_SEARCH_PARALLEL_PATH_HH__

#include <gecode/search.hh>

namespace Gecode { namespace Search { namespace Parallel {

  class Path {
  public:
    class Edge {
    protected:
      Space* _space;
      unsigned int _alt;
      unsigned int _alt_max;
      const Choice* _choice;
    public:
      Edge(void);
      Edge(Space* s, Space* c);
      
      Space* space(void) const;
      void space(Space* s);
      
      const Choice* choice(void) const;
      
      unsigned int alt(void) const;
      bool rightmost(void) const;
      bool lao(void) const;
      bool work(void) const;
      void next(void);
      unsigned int steal(void);
      
      void dispose(void);
    };
  protected:
    Support::DynamicStack<Edge,Heap> ds;
    unsigned int n_work;
  public:
    Path(void);
    const Choice* push(Worker& stat, Space* s, Space* c);
    bool next(Worker& s);
    Edge& top(void) const;
    bool empty(void) const;
    int lc(void) const;
    void unwind(int l);
    void commit(Space* s, int i) const;
    Space* recompute(unsigned int& d, unsigned int a_d, Worker& s);
    Space* recompute(unsigned int& d, unsigned int a_d, Worker& s,
                     const Space* best, int& mark);
    int entries(void) const;
    size_t size(void) const;
    void reset(void);
    bool steal(void) const;
    Space* steal(Worker& stat, unsigned long int& d);
  };


  /*
   * Edge for recomputation
   *
   */
  forceinline
  Path::Edge::Edge(void) {}

  forceinline
  Path::Edge::Edge(Space* s, Space* c)
    : _space(c), _alt(0), _choice(s->choice()) {
    _alt_max = _choice->alternatives()-1;
  }

  forceinline Space*
  Path::Edge::space(void) const {
    return _space;
  }
  forceinline void
  Path::Edge::space(Space* s) {
    _space = s;
  }

  forceinline unsigned int
  Path::Edge::alt(void) const {
    return _alt;
  }
  forceinline bool
  Path::Edge::rightmost(void) const {
    return _alt >= _alt_max;
  }
  forceinline bool
  Path::Edge::lao(void) const {
    return _alt > _alt_max;
  }
  forceinline bool
  Path::Edge::work(void) const {
    return _alt < _alt_max;
  }
  forceinline void
  Path::Edge::next(void) {
    _alt++;
  }
  forceinline unsigned int
  Path::Edge::steal(void) {
    assert(work());
    return _alt_max--;
  }

  forceinline const Choice*
  Path::Edge::choice(void) const {
    return _choice;
  }

  forceinline void
  Path::Edge::dispose(void) {
    delete _space;
    delete _choice;
  }



  /*
   * Depth-first stack with recomputation
   *
   */

  forceinline
  Path::Path(void) : ds(heap), n_work(0) {}

  forceinline const Choice*
  Path::push(Worker& stat, Space* s, Space* c) {
    if (!ds.empty() && ds.top().lao()) {
      // Topmost stack entry was LAO -> reuse
      stat.pop(ds.top().space(),ds.top().choice());
      ds.pop().dispose();
    }
    Edge sn(s,c);
    if (sn.work())
      n_work++;
    ds.push(sn);
    stat.stack_depth(static_cast<unsigned long int>(ds.entries()));
    return sn.choice();
  }

  forceinline bool
  Path::next(Worker& stat) {
    while (!ds.empty())
      if (ds.top().rightmost()) {
        stat.pop(ds.top().space(),ds.top().choice());
        ds.pop().dispose();
      } else {
        assert(ds.top().work());
        ds.top().next();
        if (!ds.top().work())
          n_work--;
        return true;
      }
    return false;
  }

  forceinline Path::Edge&
  Path::top(void) const {
    assert(!ds.empty());
    return ds.top();
  }

  forceinline bool
  Path::empty(void) const {
    return ds.empty();
  }

  forceinline void
  Path::commit(Space* s, int i) const {
    const Edge& n = ds[i];
    s->commit(*n.choice(),n.alt());
  }

  forceinline int
  Path::lc(void) const {
    int l = ds.entries()-1;
    while (ds[l].space() == NULL)
      l--;
    return l;
  }

  forceinline int
  Path::entries(void) const {
    return ds.entries();
  }

  forceinline size_t
  Path::size(void) const {
    return ds.size();
  }

  forceinline void
  Path::unwind(int l) {
    assert((ds[l].space() == NULL) || ds[l].space()->failed());
    int n = ds.entries();
    for (int i=l; i<n; i++) {
      if (ds.top().work())
        n_work--;
      ds.pop().dispose();
    }
    assert(ds.entries() == l);
  }

  forceinline void
  Path::reset(void) {
    n_work = 0;
    while (!ds.empty())
      ds.pop().dispose();
  }

  forceinline bool
  Path::steal(void) const {
    return n_work > Config::steal_limit;
  }

  forceinline Space*
  Path::steal(Worker& stat, unsigned long int& d) {
    // Find position to steal: leave sufficient work
    int n = ds.entries()-1;
    unsigned int w = 0;
    while (n >= 0) {
      if (ds[n].work())
        w++;
      if (w > Config::steal_limit) {
        // Okay, there is sufficient work left
        int l=n;
        // Find last copy
        while (ds[l].space() == NULL)
          l--;
        Space* c = ds[l].space()->clone(false);
        // Recompute, if necessary
        for (int i=l; i<n; i++)
          commit(c,i);
        c->commit(*ds[n].choice(),ds[n].steal());
        if (!ds[n].work())
          n_work--;
        d = stat.steal_depth(static_cast<unsigned long int>(n+1));
        return c;
      }
      n--;
    }
    return NULL;
  }

  forceinline Space*
  Path::recompute(unsigned int& d, unsigned int a_d, Worker& stat) {
    assert(!ds.empty());
    // Recompute space according to path
    // Also say distance to copy (d == 0) requires immediate copying

    // Check for LAO
    if ((ds.top().space() != NULL) && ds.top().rightmost()) {
      Space* s = ds.top().space();
      stat.lao(s);
      s->commit(*ds.top().choice(),ds.top().alt());
      assert(ds.entries()-1 == lc());
      ds.top().space(NULL);
      // Mark as reusable
      ds.top().next();
      d = 0;
      return s;
    }
    // General case for recomputation
    int l = lc();             // Position of last clone
    int n = ds.entries();     // Number of stack entries
    // New distance, if no adaptive recomputation
    d = static_cast<unsigned int>(n - l);

    Space* s = ds[l].space()->clone(); // Last clone

    if (d < a_d) {
      // No adaptive recomputation
      for (int i=l; i<n; i++)
        commit(s,i);
    } else {
      int m = l + static_cast<int>(d >> 1); // Middle between copy and top
      int i = l; // To iterate over all entries
      // Recompute up to middle
      for (; i<m; i++ )
        commit(s,i);
      // Skip over all rightmost branches
      for (; (i<n) && ds[i].rightmost(); i++)
        commit(s,i);
      // Is there any point to make a copy?
      if (i<n-1) {
        // Propagate to fixpoint
        SpaceStatus ss = s->status(stat);
        /*
         * Again, the space might already propagate to failure (due to
         * weakly monotonic propagators).
         */
        if (ss == SS_FAILED) {
          // s must be deleted as it is not on the stack
          delete s;
          stat.fail++;
          unwind(i);
          return NULL;
        }
        ds[i].space(s->clone());
        stat.adapt(ds[i].space());
        d = static_cast<unsigned int>(n-i);
      }
      // Finally do the remaining commits
      for (; i<n; i++)
        commit(s,i);
    }
    return s;
  }

  forceinline Space*
  Path::recompute(unsigned int& d, unsigned int a_d, Worker& stat,
                  const Space* best, int& mark) {
    assert(!ds.empty());
    // Recompute space according to path
    // Also say distance to copy (d == 0) requires immediate copying

    // Check for LAO
    if ((ds.top().space() != NULL) && ds.top().rightmost()) {
      Space* s = ds.top().space();
      stat.lao(s);
      s->commit(*ds.top().choice(),ds.top().alt());
      assert(ds.entries()-1 == lc());
      if (mark > ds.entries()-1) {
        mark = ds.entries()-1;
        s->constrain(*best);
      }
      ds.top().space(NULL);
      // Mark as reusable
      ds.top().next();
      d = 0;
      return s;
    }
    // General case for recomputation
    int l = lc();             // Position of last clone
    int n = ds.entries();     // Number of stack entries
    // New distance, if no adaptive recomputation
    d = static_cast<unsigned int>(n - l);

    Space* s = ds[l].space(); // Last clone

    if (l < mark) {
      mark = l;
      s->constrain(*best);
      // The space on the stack could be failed now as an additional
      // constraint might have been added.
      if (s->status(stat) == SS_FAILED) {
        // s does not need deletion as it is on the stack (unwind does this)
        stat.fail++;
        unwind(l);
        return NULL;
      }
      // It is important to replace the space on the stack with the
      // copy: a copy might be much smaller due to flushed caches
      // of propagators
      Space* c = s->clone();
      ds[l].space(c);
      stat.constrained(s,c);
    } else {
      s = s->clone();
    }

    if (d < a_d) {
      // No adaptive recomputation
      for (int i=l; i<n; i++)
        commit(s,i);
    } else {
      int m = l + static_cast<int>(d >> 1); // Middle between copy and top
      int i = l;            // To iterate over all entries
      // Recompute up to middle
      for (; i<m; i++ )
        commit(s,i);
      // Skip over all rightmost branches
      for (; (i<n) && ds[i].rightmost(); i++)
        commit(s,i);
      // Is there any point to make a copy?
      if (i<n-1) {
        // Propagate to fixpoint
        SpaceStatus ss = s->status(stat);
        /*
         * Again, the space might already propagate to failure
         *
         * This can be for two reasons:
         *  - constrain is true, so we fail
         *  - the space has weakly monotonic propagators
         */
        if (ss == SS_FAILED) {
          // s must be deleted as it is not on the stack
          delete s;
          stat.fail++;
          unwind(i);
          return NULL;
        }
        ds[i].space(s->clone());
        stat.adapt(ds[i].space());
        d = static_cast<unsigned int>(n-i);
      }
      // Finally do the remaining commits
      for (; i<n; i++)
        commit(s,i);
    }
    return s;
  }

}}}

#endif

// STATISTICS: search-parallel