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48b5ec569b
Atomic enforces usage of its only safe constructor, in contrast to std::atomic. "The default-initialized std::atomic<T> does not contain a T object, and its only valid uses are destruction and initialization by std::atomic_init, see LWG issue 2334." -- https://en.cppreference.com/w/cpp/atomic/atomic/atomic
72 lines
1.3 KiB
C++
72 lines
1.3 KiB
C++
/* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
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#ifndef LAZY_INIT
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#define LAZY_INIT
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#include "base/atomic.hpp"
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#include <functional>
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#include <mutex>
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#include <utility>
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namespace icinga
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{
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/**
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* Lazy object initialization abstraction inspired from
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* <https://docs.microsoft.com/en-us/dotnet/api/system.lazy-1?view=netframework-4.7.2>.
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*
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* @ingroup base
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*/
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template<class T>
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class LazyInit
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{
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public:
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inline
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LazyInit(std::function<T()> initializer = []() { return T(); }) : m_Initializer(std::move(initializer))
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{
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}
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LazyInit(const LazyInit&) = delete;
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LazyInit(LazyInit&&) = delete;
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LazyInit& operator=(const LazyInit&) = delete;
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LazyInit& operator=(LazyInit&&) = delete;
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inline
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~LazyInit()
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{
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auto ptr (m_Underlying.load(std::memory_order_acquire));
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if (ptr != nullptr) {
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delete ptr;
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}
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}
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inline
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T& Get()
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{
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auto ptr (m_Underlying.load(std::memory_order_acquire));
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if (ptr == nullptr) {
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std::unique_lock<std::mutex> lock (m_Mutex);
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ptr = m_Underlying.load(std::memory_order_acquire);
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if (ptr == nullptr) {
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ptr = new T(m_Initializer());
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m_Underlying.store(ptr, std::memory_order_release);
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}
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}
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return *ptr;
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}
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private:
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std::function<T()> m_Initializer;
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std::mutex m_Mutex;
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Atomic<T*> m_Underlying {nullptr};
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};
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}
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#endif /* LAZY_INIT */
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