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/* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
#ifndef LAZY_INIT
#define LAZY_INIT
#include <atomic>
#include <functional>
#include <mutex>
#include <utility>
namespace icinga
{
/**
* Lazy object initialization abstraction inspired from
* <https://docs.microsoft.com/en-us/dotnet/api/system.lazy-1?view=netframework-4.7.2>.
*
* @ingroup base
*/
template<class T>
class LazyInit
{
public:
inline
LazyInit(std::function<T()> initializer = []() { return T(); }) : m_Initializer(std::move(initializer))
{
m_Underlying.store(nullptr, std::memory_order_release);
}
LazyInit(const LazyInit&) = delete;
LazyInit(LazyInit&&) = delete;
LazyInit& operator=(const LazyInit&) = delete;
LazyInit& operator=(LazyInit&&) = delete;
inline
~LazyInit()
{
auto ptr (m_Underlying.load(std::memory_order_acquire));
if (ptr != nullptr) {
delete ptr;
}
}
inline
T& Get()
{
auto ptr (m_Underlying.load(std::memory_order_acquire));
if (ptr == nullptr) {
std::unique_lock<std::mutex> lock (m_Mutex);
ptr = m_Underlying.load(std::memory_order_acquire);
if (ptr == nullptr) {
ptr = new T(m_Initializer());
m_Underlying.store(ptr, std::memory_order_release);
}
}
return *ptr;
}
private:
std::function<T()> m_Initializer;
std::mutex m_Mutex;
std::atomic<T*> m_Underlying;
};
}
#endif /* LAZY_INIT */
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