[wpiutil] Add MappedFileRegion

wpiutil/src/main/native/include/wpi/MappedFileRegion.h

@@ -0,0 +1,86 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <stdint.h>
+
+#include <system_error>
+
+// Duplicated from fs.h to avoid a dependency
+namespace fs {
+#if defined(_WIN32)
+// A Win32 HANDLE is a typedef of void*
+using file_t = void*;
+#else
+using file_t = int;
+#endif
+}  // namespace fs
+
+namespace wpi {
+
+class MappedFileRegion {
+ public:
+  enum MapMode {
+    kReadOnly,   ///< May only access map via const_data as read only.
+    kReadWrite,  ///< May access map via data and modify it. Written to path.
+    kPriv        ///< May modify via data, but changes are lost on destruction.
+  };
+
+  MappedFileRegion() = default;
+  MappedFileRegion(fs::file_t f, uint64_t length, uint64_t offset,
+                   MapMode mapMode, std::error_code& ec);
+  ~MappedFileRegion() { Unmap(); }
+
+  MappedFileRegion(const MappedFileRegion&) = delete;
+  MappedFileRegion& operator=(const MappedFileRegion&) = delete;
+
+  MappedFileRegion(MappedFileRegion&& rhs)
+      : m_size(rhs.m_size), m_mapping(rhs.m_mapping) {
+    rhs.m_mapping = nullptr;
+#ifdef _WIN32
+    m_fileHandle = rhs.m_fileHandle;
+    rhs.m_fileHandle = nullptr;
+#endif
+  }
+
+  MappedFileRegion& operator=(MappedFileRegion&& rhs) {
+    if (m_mapping) {
+      Unmap();
+    }
+    m_size = rhs.m_size;
+    m_mapping = rhs.m_mapping;
+    rhs.m_mapping = nullptr;
+#ifdef _WIN32
+    m_fileHandle = rhs.m_fileHandle;
+    rhs.m_fileHandle = nullptr;
+#endif
+    return *this;
+  }
+
+  explicit operator bool() const { return m_mapping != nullptr; }
+
+  void Flush();
+  void Unmap();
+
+  uint64_t size() const { return m_size; }
+  uint8_t* data() const { return static_cast<uint8_t*>(m_mapping); }
+  const uint8_t* const_data() const {
+    return static_cast<const uint8_t*>(m_mapping);
+  }
+
+  /**
+   * Returns required alignment.
+   */
+  static size_t GetAlignment();
+
+ private:
+  uint64_t m_size = 0;
+  void* m_mapping = nullptr;
+#ifdef _WIN32
+  fs::file_t m_fileHandle = nullptr;
+#endif
+};
+
+}  // namespace wpi