2020-11-16 14:47:43 +08:00
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//////////////////////////////////////////////////////////////////////////////////////////
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2023-05-14 17:06:43 +08:00
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// A multi-platform support c++11 library with focus on asynchronous socket I/O for any
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2021-01-14 15:30:18 +08:00
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// client application.
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2020-11-16 14:47:43 +08:00
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//////////////////////////////////////////////////////////////////////////////////////////
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/*
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The MIT License (MIT)
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2023-01-01 17:36:38 +08:00
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Copyright (c) 2012-2023 HALX99
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2020-11-16 14:47:43 +08:00
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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*/
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2023-05-15 16:57:02 +08:00
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// core/singleton.hpp: A common use thread safe singleton class template, support non-delayed or delayed init with variadic args.
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//
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// refer to:
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// https://www.youtube.com/watch?v=c1gO9aB9nbs&t=1120s
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//
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// remark:
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// Singletons make it hard to determine the lifetime of an object, which can
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// lead to buggy code and spurious crashes.
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//
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// Instead of adding another singleton into the mix, try to identify either:
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// a) An existing singleton that can manage your object's lifetime
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// b) Locations where you can deterministically create the object and pass
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// into other objects
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//
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// If you absolutely need a singleton, please keep them as trivial as possible
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// and ideally a leaf dependency. Singletons get problematic when they attempt
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// to do too much in their destructor or have circular dependencies.
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#ifndef YASIO__SINGLETON_HPP
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#define YASIO__SINGLETON_HPP
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#include <new>
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#include <memory>
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#include <functional>
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#include <mutex>
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#include <atomic>
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2023-05-14 22:39:05 +08:00
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#include "yasio/config.hpp"
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namespace yasio
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{
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template <typename _Ty, bool delay = false>
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class singleton_constructor {
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public:
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template <typename... _Types>
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static _Ty* construct(_Types&&... args)
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{
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return new _Ty(std::forward<_Types>(args)...);
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}
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};
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template <typename _Ty>
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class singleton_constructor<_Ty, true> {
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public:
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template <typename... _Types>
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static _Ty* construct(_Types&&... args)
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{
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auto inst = new _Ty();
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delay_init(inst, std::forward<_Types>(args)...);
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return inst;
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}
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private:
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template <typename _Fty, typename... _Types>
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static void delay_init(_Ty* inst, _Fty&& memf, _Types&&... args)
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{ // init use specific member func with more than 1 args
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std::mem_fn(memf)(inst, std::forward<_Types>(args)...);
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}
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template <typename _Fty, typename _Arg>
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static void delay_init(_Ty* inst, _Fty&& memf, _Arg&& arg)
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{ // init use specific member func with 1 arg
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std::mem_fn(memf)(inst, std::forward<_Arg>(arg));
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}
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template <typename _Fty>
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static void delay_init(_Ty* inst, _Fty&& memf)
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{ // init use specific member func without arg
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std::mem_fn(memf)(inst);
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}
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static void delay_init(_Ty* inst)
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{ // dummy init without delay init member func, same as no delay constructor
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}
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};
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template <typename _Ty>
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class singleton {
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typedef singleton<_Ty> _Myt;
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typedef _Ty* pointer;
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public:
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// Return the singleton instance
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template <typename... _Types>
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static pointer instance(_Types&&... args)
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{
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return get_instance<false>(std::forward<_Types>(args)...);
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}
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template <typename... _Types>
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static pointer instance1(_Types&&... args)
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{
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return get_instance<true>(std::forward<_Types>(args)...);
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}
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static void destroy(void)
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{
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if (auto inst = _Myt::__single__.exchange(nullptr, std::memory_order_acq_rel))
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delete inst;
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}
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// Peek the singleton instance
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static pointer peek() { return _Myt::__single__; }
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private:
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template <bool delay, typename... _Types>
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static pointer get_instance(_Types&&... args)
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{
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auto& inst = _Myt::__single__;
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if (inst.load(std::memory_order_acquire))
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return inst;
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{
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std::lock_guard<std::mutex> lck(__mutex__);
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if (!inst.load(std::memory_order_relaxed))
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inst.store(singleton_constructor<_Ty, delay>::construct(std::forward<_Types>(args)...), std::memory_order_release);
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}
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return inst;
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}
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2020-11-16 14:47:43 +08:00
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static std::atomic<_Ty*> __single__;
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static std::mutex __mutex__;
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private:
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// disable construct, assign operation, copy construct also not allowed.
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singleton(void) = delete;
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};
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template <typename _Ty>
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std::atomic<_Ty*> singleton<_Ty>::__single__;
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template <typename _Ty>
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std::mutex singleton<_Ty>::__mutex__;
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2020-11-16 14:47:43 +08:00
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} // namespace yasio
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#endif
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