singleton.hpp

/* -*- mode: c++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 
/*
 Copyright (C) 2004, 2005, 2007 StatPro Italia srl
 
 This file is part of QuantLib, a free-software/open-source library
 for financial quantitative analysts and developers - http://quantlib.org/
 
 QuantLib is free software: you can redistribute it and/or modify it
 under the terms of the QuantLib license.  You should have received a
 copy of the license along with this program; if not, please email
 <quantlib-dev@lists.sf.net>. The license is also available online at
 <http://quantlib.org/license.shtml>.
 
 This program is distributed in the hope that it will be useful, but WITHOUT
 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 FOR A PARTICULAR PURPOSE.  See the license for more details.
*/
 
#ifndef quantlib_singleton_hpp
#define quantlib_singleton_hpp
 
#include <ql/types.hpp>
#include <type_traits>
 
namespace QuantLib {
 
 
    template <class T, class Global = std::integral_constant<bool, false> >
    class Singleton {
      public:
        // disable copy/move
        Singleton(const Singleton&) = delete;
        Singleton(Singleton&&) = delete;
        Singleton& operator=(const Singleton&) = delete;
        Singleton& operator=(Singleton&&) = delete;
        ~Singleton() = default;
 
        static T& instance();
 
      protected:
        Singleton() = default;
    };
 
    // template definitions
 
#ifdef QL_ENABLE_SESSIONS
 
#if (defined(__GNUC__) && !defined(__clang__)) && (((__GNUC__ == 8) && (__GNUC_MINOR__ < 4)) || (__GNUC__ < 8))
#pragma message("Singleton::instance() is always compiled with `-O0` for versions of GCC below 8.4 when sessions are enabled.")
#pragma message("This is to work around the following compiler bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91757")
#pragma message("If possible, please update your compiler to a more recent version.")
#pragma GCC push_options
#pragma GCC optimize("-O0")
#endif
 
    template <class T, class Global>
    T& Singleton<T, Global>::instance() {
        if(Global()) {
            static T global_instance;
            return global_instance;
        } else {
            thread_local static T local_instance;
            return local_instance;
        }
    }
 
#if (defined(__GNUC__) && !defined(__clang__)) && (((__GNUC__ == 8) && (__GNUC_MINOR__ < 4)) || (__GNUC__ < 8))
#pragma GCC pop_options
#endif
 
#else
 
    template <class T, class Global>
    T& Singleton<T, Global>::instance() {
        static T instance;
        return instance;
    }
 
#endif
 
    // backwards compatibility
 
#if defined(QL_THREAD_KEY)
    QL_DEPRECATED
    typedef QL_THREAD_KEY ThreadKey;
#else
    QL_DEPRECATED
    typedef Integer ThreadKey;
#endif
 
}
 
#endif