1 files changed, 72 insertions, 0 deletions
diff --git a/lib/base/lazy-init.hpp b/lib/base/lazy-init.hpp
new file mode 100644
index 0000000..c1da2cd
--- /dev/null
+++ b/lib/base/lazy-init.hpp
@@ -0,0 +1,72 @@
+/* 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 */