dal_singleton.h

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/* -*- c++ -*- (enables emacs c++ mode) */
/*===========================================================================
 
 Copyright (C) 2004-2026 Julien Pommier
 
 This file is a part of GetFEM
 
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 under  the  terms  of the  GNU  Lesser General Public License as published
 by  the  Free Software Foundation;  either version 3 of the License,  or
 (at your option) any later version along with the GCC Runtime Library
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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.
 You  should  have received a copy of the GNU Lesser General Public License
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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 distributed MPI-like
environment;
*/
 
#pragma once
 
#include <vector>
#include <memory>
 
#include "getfem_omp.h"
 
 
namespace dal {
 
  using bgeot::size_type;
 
  class singleton_instance_base {
  public:
    virtual ~singleton_instance_base() {};
    virtual int level() const = 0;
  };
 
  class singletons_manager {
    getfem::omp_distribute<std::vector<singleton_instance_base *>> lst;
    size_type nb_partitions;
    static singletons_manager& manager();
 
  public:
    static void register_new_singleton(singleton_instance_base *p);
    static void register_new_singleton(singleton_instance_base *p,
                                       size_t ithread);
    static void on_partitions_change();
 
    /**destroy singletons in increasing order*/
    ~singletons_manager();
 
  private:
    singletons_manager();
  };
 
  template <typename T, int LEV>
  class singleton_instance : public singleton_instance_base {
 
    static getfem::omp_distribute<T*>* initializing_pointer;
 
    static getfem::omp_distribute<T*>*& pointer() {
      static auto p = new getfem::omp_distribute<T*>{};
      return p;
    }
 
    static T*& instance_pointer() {
      return pointer()->thrd_cast();
    }
 
    static T*& instance_pointer(size_t ithread) {
      return (*pointer())(ithread);
    }
 
  public:
 
    /**Instance from thread ithread*/
    inline static T& instance(size_t ithread) {
      pointer()->on_thread_update();
      T*& tinstance_ = instance_pointer(ithread);
      if (!tinstance_) {
        tinstance_ = new T();
        singletons_manager::register_new_singleton(
          new singleton_instance<T,LEV>(), ithread);
      }
      return *instance_pointer(ithread);
    }
 
    /** Instance from the current thread*/
    inline static T& instance() {
      return instance(this_thread());
    }
 
    inline static size_type num_threads() {
      return pointer()->num_threads();
    }
 
    inline static size_type this_thread() {
      return pointer()->this_thread();
    }
 
    int level() const override {
      return LEV;
    }
 
    ~singleton_instance() {
      if (!pointer()) return;
      for(size_t i = 0; i != pointer()->num_threads(); ++i) {
        auto &p_singleton = (*pointer())(i);
        if(p_singleton){
          delete p_singleton;
          p_singleton = nullptr;
        }
      }
      delete pointer();
      pointer() = nullptr;
      if (initializing_pointer) initializing_pointer = nullptr;
    }
  };
 
  template<typename T, int LEV> getfem::omp_distribute<T*>*
  singleton_instance<T, LEV>::initializing_pointer = singleton_instance<T, LEV>::pointer();
 
  /** 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:
 
    singleton(const singleton&) = delete;
    singleton& operator=(const singleton&) = delete;
 
    /** 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);
    }
 
    /** number of threads this singleton is distributed on.*/
    inline static size_type num_threads(){
      return singleton_instance<T,LEV>::num_threads();
    }
 
    /** this thread number according to the threading policy of the singleton*/
    inline static size_type this_thread() {
      return singleton_instance<T, LEV>::this_thread();
    }
 
  protected:
    singleton() = default;
    ~singleton() = default;
  };
 
}/* end of namespace dal                                                             */