json/detail/default_resource.hpp

0001 //
0002 // Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
0003 //
0004 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0005 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 //
0007 // Official repository: https://github.com/boostorg/json
0008 //
0009
0010 #ifndef BOOST_JSON_DEFAULT_RESOURCE_HPP
0011 #define BOOST_JSON_DEFAULT_RESOURCE_HPP
0012
0013 #include <boost/json/detail/config.hpp>
0014 #include <new>
0015
0016 namespace boost {
0017 namespace json {
0018 namespace detail {
0019
0020 #ifdef _MSC_VER
0021 #pragma warning(push)
0022 #pragma warning(disable: 4251) // class needs to have dll-interface to be used by clients of class
0023 #pragma warning(disable: 4275) // non dll-interface class used as base for dll-interface class
0024 #endif
0025
0026 // A simple memory resource that uses operator new and delete.
0027 class
0028     BOOST_SYMBOL_VISIBLE
0029     BOOST_JSON_DECL
0030 default_resource final
0031     : public memory_resource
0032 {
0033     union holder;
0034
0035 #ifndef BOOST_JSON_WEAK_CONSTINIT
0036 # ifndef BOOST_JSON_NO_DESTROY
0037     static holder instance_;
0038 # else
0039     BOOST_JSON_NO_DESTROY
0040     static default_resource instance_;
0041 # endif
0042 #endif
0043
0044 public:
0045     static
0046     memory_resource*
0047     get() noexcept
0048     {
0049     #ifdef BOOST_JSON_WEAK_CONSTINIT
0050         static default_resource instance_;
0051     #endif
0052         return reinterpret_cast<memory_resource*>(
0053             reinterpret_cast<std::uintptr_t*>(
0054                 &instance_));
0055     }
0056
0057     ~default_resource();
0058
0059     void*
0060     do_allocate(
0061         std::size_t n,
0062         std::size_t) override;
0063
0064     void
0065     do_deallocate(
0066         void* p,
0067         std::size_t,
0068         std::size_t) override;
0069
0070     bool
0071     do_is_equal(
0072         memory_resource const& mr) const noexcept override;
0073 };
0074
0075 #ifdef _MSC_VER
0076 #pragma warning(pop)
0077 #endif
0078
0079 union default_resource::
0080     holder
0081 {
0082 #ifndef BOOST_JSON_WEAK_CONSTINIT
0083     constexpr
0084 #endif
0085     holder()
0086         : mr()
0087     {
0088     }
0089
0090     ~holder()
0091     {
0092     }
0093
0094     default_resource mr;
0095 };
0096
0097 } // detail
0098 } // namespace json
0099 } // namespace boost
0100
0101 #endif