dal_singleton.h

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

 Copyright (C) 2004-2017 Julien Pommier

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/**@file dal_singleton.h
@author  Julien Pommier <Julien.Pommier@insa-toulouse.fr>
@date May 2004.
@brief A simple singleton implementation

Singleton was made thread safe for OpenMP
However, now there is a singleton instance for every 
thread (singleton is thread local). This replicates
the behaviour of singletons in distirbuted MPI-like 
environment;
*/
#ifndef DAL_SINGLETON
#define DAL_SINGLETON

#include <vector>
#include <memory>
#include "getfem_omp.h"


namespace dal {

  class singleton_instance_base {
  public:
    virtual ~singleton_instance_base() {}
    virtual int level() = 0;
  };


  class singletons_manager {
  protected:
    getfem::omp_distribute<std::vector<singleton_instance_base *>> lst;
    static singletons_manager& manager();
    static singletons_manager& m;

  public:
    static void register_new_singleton(singleton_instance_base *p);
    static void register_new_singleton(singleton_instance_base *p,
                                       size_t ithread);
    ~singletons_manager();
  private:
    singletons_manager();
  };




  template <typename T, int LEV> class singleton_instance
    : public singleton_instance_base {
    static getfem::omp_distribute<T*>* instance_;
    static getfem::omp_distribute<T*>* omp_distro_pointer() {
      static getfem::omp_distribute<T*>*
        pointer = new getfem::omp_distribute<T*>();
      return pointer;
    }
    static T*& instance_pointer() { return omp_distro_pointer()->thrd_cast(); }
    static T*& instance_pointer(size_t ithread)
    { return (*omp_distro_pointer())(ithread);}
    
  public:
    
    singleton_instance() {}
    
    /** Instance from the current thread*/
    inline static T& instance() { 
      T*& tinstance_ = instance_pointer();
      if (!tinstance_) {
        tinstance_ = new T();
        singletons_manager::register_new_singleton
          (new singleton_instance<T,LEV>());
      }
      return *tinstance_; 
    }
    
    /**Instance from thread ithread*/
    inline static T& instance(size_t ithread) { 
      T*& tinstance_ = instance_pointer(ithread);
      if (!tinstance_) {
        tinstance_ = new T();
        singletons_manager::register_new_singleton
          (new singleton_instance<T,LEV>(),ithread);
      }
      return *tinstance_; 
    }
    
    int level() { return LEV; }
    
    ~singleton_instance() {
      if (instance_) {
        for(size_t i = 0; i < getfem::num_threads(); i++) {
          if((*instance_)(i))  { 
            delete (*instance_)(i); 
            (*instance_)(i) = 0; 
          }
        } 
      }
      delete instance_; instance_=0;
    }
  };

  /** singleton class. 
      
      usage: 
      @code
      foo &f = singleton<foo>::instance();
      const foo &f = singleton<foo>::const_instance();
      @endcode
      the LEV template arguments allows one to choose the order of destruction
      of the singletons:
      lowest LEV will be destroyed first.
  */
  template <typename T, int LEV=1> class singleton {
  public:
    
    /** Instance from the current thread*/
    inline static T& instance() { 
      return singleton_instance<T,LEV>::instance();
    }
    inline static const T& const_instance() { return instance(); }

    inline static T& instance(size_t ithread) { 
      return singleton_instance<T,LEV>::instance(ithread);
    }
    inline static const T& const_instance(size_t ithread)
    { return instance(ithread); }

    
  protected:
    singleton() {}
    ~singleton() {}
  private:
    singleton(const singleton&);            
    singleton& operator=(const singleton&);
  };
  
  template <typename T, int LEV> 
  getfem::omp_distribute<T*>* singleton_instance<T,LEV>::instance_
  = singleton_instance<T,LEV>::omp_distro_pointer();
}

#endif