rx: add mappable resource utility

rx/include/rx/Mappable.hpp

@@ -0,0 +1,60 @@
+#pragma once
+
+#include "AddressRange.hpp"
+#include "EnumBitSet.hpp"
+#include <system_error>
+#include <utility>
+
+namespace rx {
+enum class Protection {
+  R,
+  W,
+  X,
+
+  bitset_last = X
+};
+
+std::errc reserveVirtualSpace(rx::AddressRange range);
+std::errc releaseVirtualSpace(rx::AddressRange range, std::size_t alignment);
+
+class Mappable {
+#ifdef _WIN32
+  using NativeHandle = void *;
+  static constexpr NativeHandle kInvalidHandle = nullptr;
+#else
+  using NativeHandle = int;
+  static constexpr auto kInvalidHandle = NativeHandle(-1);
+#endif
+
+  NativeHandle m_handle = kInvalidHandle;
+
+public:
+  Mappable() = default;
+  Mappable(Mappable &&other) noexcept { *this = std::move(other); }
+  Mappable(const Mappable &) = delete;
+  Mappable &operator=(Mappable &&other) noexcept {
+    std::swap(m_handle, other.m_handle);
+    return *this;
+  }
+  Mappable &operator=(const Mappable &) = delete;
+  ~Mappable() noexcept {
+    if (m_handle != kInvalidHandle) {
+      destroy();
+    }
+  }
+
+  static std::pair<Mappable, std::errc> CreateMemory(std::size_t size);
+  static std::pair<Mappable, std::errc> CreateSwap(std::size_t size);
+  std::errc map(rx::AddressRange virtualRange, std::size_t offset,
+                rx::EnumBitSet<Protection> protection, std::size_t alignment);
+
+  [[nodiscard]] NativeHandle release() {
+    return std::exchange(m_handle, kInvalidHandle);
+  }
+  [[nodiscard]] NativeHandle native_handle() const { return m_handle; }
+  explicit operator bool() const { return m_handle != kInvalidHandle; }
+
+private:
+  void destroy();
+};
+} // namespace rx