Introduce id_dispenser class

nano/lib/CMakeLists.txt

@@ -36,6 +36,7 @@ add_library(
   epoch.cpp
   errors.hpp
   errors.cpp
+  id_dispenser.hpp
   ipc.hpp
   ipc.cpp
   ipc_client.hpp

nano/lib/id_dispenser.hpp

@@ -0,0 +1,62 @@
+#pragma once
+
+#include <atomic>
+#include <random>
+
+namespace nano
+{
+class id_dispenser
+{
+public:
+	enum class mode
+	{
+		sequential,
+		random,
+	};
+
+	// Using pointer type for prettier and more concise output in logs (hex)
+	using id_t = void *;
+
+public:
+	explicit id_dispenser (mode mode = mode::random) :
+		mode_m{ mode }
+	{
+	}
+
+	id_t next_id ()
+	{
+		switch (mode_m)
+		{
+			case mode::sequential:
+				return reinterpret_cast<id_t> (current_id_m.fetch_add (1));
+			case mode::random:
+				auto value = get_dist () (get_rng ());
+				if (value < min_m)
+				{
+					value += min_m;
+				}
+				return reinterpret_cast<id_t> (value);
+		}
+		return 0;
+	}
+
+private:
+	// Avoid IDs with leading 0s for nicer output in logs
+	static constexpr uint64_t min_m{ 0x1000000000000000 };
+
+	mode mode_m;
+	std::atomic<uint64_t> current_id_m{ min_m };
+
+	static std::mt19937 & get_rng ()
+	{
+		static thread_local std::mt19937 rng{ std::random_device{}() };
+		return rng;
+	}
+
+	static std::uniform_int_distribution<uint64_t> & get_dist ()
+	{
+		static thread_local std::uniform_int_distribution<uint64_t> dist;
+		return dist;
+	}
+};
+}