getfem_context.h

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/* -*- c++ -*- (enables emacs c++ mode) */
/*===========================================================================

 Copyright (C) 2004-2017 Yves Renard

 This file is a part of GetFEM++

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 under  the  terms  of the  GNU  Lesser General Public License as published
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 (at your option) any later version along with the GCC Runtime Library
 Exception either version 3.1 or (at your option) any later version.
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 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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 License and GCC Runtime Library Exception for more details.
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/**@file getfem_context.h
   @author  Yves Renard <Yves.Renard@insa-lyon.fr>
   @date June 17, 2004.
   @brief Deal with interdependencies of objects (getfem::context_dependencies).
*/
#ifndef GETFEM_CONTEXT_H__
#define GETFEM_CONTEXT_H__

#include "getfem_config.h"
#include "getfem_omp.h"
#include <list>

#ifdef GETFEM_HAVE_OPENMP
  #include <boost/atomic.hpp>
  typedef boost::atomic_bool atomic_bool;
#else
  typedef bool  atomic_bool;
#endif


namespace getfem {
  /**Deal with interdependencies of objects.

   An object can be in three different states :
     NORMAL  : no change is necessary
     CHANGED : something in the context has changed and the update function
               of the object has to be called.
     INVALID : one of the dependencies desappears, the object is invalid
               and should no longer be used.
  
   add_dependency(ct) : add a dependency to the dependency list.

   touch()            : significate to the dependent objects that something
                        has change in the object. This make the dependent
                        objects to be in the CHANGED state

   context_check()    : check if the object has to be updated. if it is the
                        case it makes first a check to the dependency list
                        and call the update function of the object.
                        (the update function of the dependencies are called
                        before the update function of the current object).

   context_valid()    : says if the object has still a valid context
  
   Remarks :

   - A protection against round dependencies exists. In this case, the
   order of call of the update functions can be arbitrary

   - Detection of context changes is very fast (control the
   state). the touch operation can cover the whole tree of dependent
   object.  But this is the case only for the first touch operation
   because once a dependent object is in the CHANGED state it will not
   be considered by next touch operations.
  */
  class APIDECL context_dependencies {

  protected :
    enum context_state { CONTEXT_NORMAL, CONTEXT_CHANGED, CONTEXT_INVALID };
    mutable context_state state;
    mutable atomic_bool touched;
    mutable std::vector<const context_dependencies *> dependencies;
    mutable std::vector<const context_dependencies *> dependent;
    typedef std::vector<const context_dependencies *>::iterator iterator_list;
    getfem::lock_factory locks_;

    void sup_dependent_(const context_dependencies &cd) const;
    void sup_dependency_(const context_dependencies &cd) const;
    void invalid_context() const;
    bool go_check() const;

  public :
    
    /** this function has to be defined and should update the object when
        the context is modified. */
    virtual void update_from_context() const = 0;

    void change_context() const
    { 
      if (state == CONTEXT_NORMAL) 
      { 
        touch(); 
        getfem::local_guard lock = locks_.get_lock();
        state = CONTEXT_CHANGED; 
      } 
    }
    void add_dependency(const context_dependencies &cd);
    
    void sup_dependency(const context_dependencies &cd)
    { 
      cd.sup_dependent_(*this); 
      sup_dependency_(cd); 
    }

    void clear_dependencies();


    bool is_context_valid() const { return (state != CONTEXT_INVALID); }
    bool is_context_changed() const { return (state == CONTEXT_CHANGED); }
    /** return true if update_from_context was called */
    bool context_check() const
    { if (state == CONTEXT_NORMAL) return false; return go_check(); }
    void touch() const;
    virtual ~context_dependencies();
    context_dependencies() : state(CONTEXT_NORMAL), touched( ) {touched = false;}
    context_dependencies(const context_dependencies& cd);
    context_dependencies& operator=(const context_dependencies& cd);
  };

}  /* end of namespace getfem.                                             */


#endif /* GETFEM_CONTEXT_H__  */