engine.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, 2009
 *
 *  Last modified:
 *     $Date: 2009-05-14 20:16:52 +0200 (Thu, 14 May 2009) $ by $Author: schulte $
 *     $Revision: 9120 $
 *
 *  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.
 *
 */

#ifndef __GECODE_SEARCH_PARALLEL_ENGINE_HH__
#define __GECODE_SEARCH_PARALLEL_ENGINE_HH__

#include <gecode/search.hh>
#include <gecode/search/support.hh>
#include <gecode/search/worker.hh>
#include <gecode/search/parallel/path.hh>

#include <gecode/support/thread.hh>

namespace Gecode { namespace Search { namespace Parallel {

  class Engine : public Search::Engine {
  protected:
    class Worker : public Search::Worker, public Support::Runnable {
    protected:
      Engine& _engine;
      Support::Mutex m;
      Path path;
      Space* cur;
      unsigned int d;
      bool idle;
    public:
      Worker(Space* s, size_t sz, Engine& e);
      Space* steal(unsigned long int& d);
      Statistics statistics(void);
      Engine& engine(void) const;
      virtual ~Worker(void);
    };
    const Options _opt;
  public:
    const Options& opt(void) const;
    unsigned int workers(void) const;
    


    enum Cmd {
      C_WORK,     
      C_WAIT,     
      C_RESET,    
      C_TERMINATE 
    };
  protected:
    volatile Cmd _cmd;
    Support::Mutex _m_wait;
  public:
    Cmd cmd(void) const;
    void block(void);
    void release(Cmd c);
    void wait(void);


  protected:
    Support::Mutex _m_term;
    volatile unsigned int _n_term_not_ack;
    Support::Event _e_term_ack;
    Support::Mutex _m_wait_terminate;
    volatile unsigned int _n_not_terminated;
    Support::Event _e_terminate;
  public:
    void ack_terminate(void);
    void terminated(void);
    void wait_terminate(void);
    void terminate(void);


  protected:
    Support::Mutex _m_reset;
    volatile unsigned int _n_reset_not_ack;
    Support::Event e_reset_ack_start;
    Support::Event e_reset_ack_stop;
    Support::Mutex m_wait_reset;
  public:
    void ack_reset_start(void);
    void ack_reset_stop(void);
    void wait_reset(void);


  protected:
    Support::Mutex m_search;
    Support::Event e_search;
    Support::DynamicQueue<Space*,Heap> solutions;
    volatile unsigned int n_busy;
    volatile bool has_stopped;
    bool signal(void) const;
  public:
    void idle(void);
    void busy(void);
    void stop(void);



    Engine(const Options& o);
    virtual Space* next(void);
    virtual bool stopped(void) const;
  };


  /*
   * Basic access routines
   */
  forceinline Engine&
  Engine::Worker::engine(void) const {
    return _engine;
  }
  forceinline const Options&
  Engine::opt(void) const {
    return _opt;
  }
  forceinline unsigned int
  Engine::workers(void) const {
    return opt().threads;
  }


  /*
   * Engine: command and wait handling
   */
  forceinline Engine::Cmd
  Engine::cmd(void) const {
    return _cmd;
  }
  forceinline void 
  Engine::block(void) {
    _cmd = C_WAIT;
    _m_wait.acquire();
  }
  forceinline void 
  Engine::release(Cmd c) {
    _cmd = c;
    _m_wait.release();
  }
  forceinline void 
  Engine::wait(void) {
    _m_wait.acquire(); _m_wait.release();
  }


  /*
   * Engine: initialization
   */
  forceinline
  Engine::Worker::Worker(Space* s, size_t sz, Engine& e)
    : Search::Worker(sz), _engine(e), d(0), idle(false) {
    if (s != NULL) {
      cur = (s->status(*this) == SS_FAILED) ? 
        NULL : snapshot(s,engine().opt());
      if (cur == NULL)
        fail++;
    } else {
      cur = NULL;
    }
    current(s);
    current(NULL);
    current(cur);
  }

  forceinline
  Engine::Engine(const Options& o)
    : _opt(o), solutions(heap) {
    // Initialize termination information
    _n_term_not_ack = workers();
    _n_not_terminated = workers();
    // Initialize search information
    n_busy = workers();
    has_stopped = false;
    // Initialize reset information
    _n_reset_not_ack = workers();
  }


  /*
   * Statistics
   */
  forceinline Statistics
  Engine::Worker::statistics(void) {
    m.acquire();
    Statistics s = *this;
    s.memory += path.size();
    m.release();
    return s;
  }


  /*
   * Engine: search control
   */
  forceinline bool
  Engine::signal(void) const {
    return solutions.empty() && (n_busy > 0) && !has_stopped;
  }
  forceinline void 
  Engine::idle(void) {
    m_search.acquire();
    bool bs = signal();
    n_busy--;
    if (bs && (n_busy == 0))
      e_search.signal();
    m_search.release();
  }
  forceinline void 
  Engine::busy(void) {
    m_search.acquire();
    assert(n_busy > 0);
    n_busy++;
    m_search.release();
  }
  forceinline void 
  Engine::stop(void) {
    m_search.acquire();
    bool bs = signal();
    has_stopped = true;
    if (bs)
      e_search.signal();
    m_search.release();
  }
  

  /*
   * Engine: termination control
   */
  forceinline void 
  Engine::terminated(void) {
    unsigned int n;
    _m_term.acquire();
    n = --_n_not_terminated;
    _m_term.release();
    // The signal must be outside of the look, otherwise a thread might be 
    // terminated that still holds a mutex.
    if (n == 0)
      _e_terminate.signal();
  }

  forceinline void 
  Engine::ack_terminate(void) {
    _m_term.acquire();
    if (--_n_term_not_ack == 0)
      _e_term_ack.signal();
    _m_term.release();
  }

  forceinline void 
  Engine::wait_terminate(void) {
    _m_wait_terminate.acquire();
    _m_wait_terminate.release();
  }

  forceinline void
  Engine::terminate(void) {
    // Grab the wait mutex for termination
    _m_wait_terminate.acquire();
    // Release all threads
    release(C_TERMINATE);
    // Wait until all threads have acknowledged termination request
    _e_term_ack.wait();
    // Release waiting threads
    _m_wait_terminate.release();    
    // Wait until all threads have in fact terminated
    _e_terminate.wait();
    // Now all threads are terminated!
  }



  /*
   * Engine: reset control
   */
  forceinline void 
  Engine::ack_reset_start(void) {
    _m_reset.acquire();
    if (--_n_reset_not_ack == 0)
      e_reset_ack_start.signal();
    _m_reset.release();
  }

  forceinline void 
  Engine::ack_reset_stop(void) {
    _m_reset.acquire();
    if (++_n_reset_not_ack == workers())
      e_reset_ack_stop.signal();
    _m_reset.release();
  }

  forceinline void 
  Engine::wait_reset(void) {
    m_wait_reset.acquire();
    m_wait_reset.release();
  }



  /*
   * Worker: finding and stealing working
   */
  forceinline Space*
  Engine::Worker::steal(unsigned long int& d) {
    /*
     * Make a quick check whether the worker might have work
     *
     * If that is not true any longer, the worker will be asked
     * again eventually.
     */
    if (!path.steal())
      return NULL;
    m.acquire();
    Space* s = path.steal(*this,d);
    m.release();
    // Tell that there will be one more busy worker
    if (s != NULL) 
      engine().busy();
    return s;
  }

}}}

#endif

// STATISTICS: search-parallel