gecko-dev/devtools/shared/heapsnapshot/AutoMemMap.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_devtools_AutoMemMap_h
#define mozilla_devtools_AutoMemMap_h

#include <prio.h>
#include "mozilla/GuardObjects.h"

namespace mozilla {
namespace devtools {

// # AutoMemMap
//
// AutoMemMap is an RAII class to manage mapping a file to memory. It is a
// wrapper aorund managing opening and closing a file and calling PR_MemMap and
// PR_MemUnmap.
//
// Example usage:
//
//     {
//       AutoMemMap mm;
//       if (NS_FAILED(mm.init("/path/to/desired/file"))) {
//          // Handle the error however you see fit.
//         return false;
//       }
//
//       doStuffWithMappedMemory(mm.address());
//     }
//     // The memory is automatically unmapped when the AutoMemMap leaves scope.
class MOZ_RAII AutoMemMap
{
  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER;

  PRFileInfo64 fileInfo;
  PRFileDesc*  fd;
  PRFileMap*   fileMap;
  void*        addr;

  AutoMemMap(const AutoMemMap& aOther) = delete;
  void operator=(const AutoMemMap& aOther) = delete;

public:
  explicit AutoMemMap(MOZ_GUARD_OBJECT_NOTIFIER_ONLY_PARAM)
      : fd(nullptr)
      , fileMap(nullptr)
      , addr(nullptr)
  {
      MOZ_GUARD_OBJECT_NOTIFIER_INIT;
  };
  ~AutoMemMap();

  // Initialize this AutoMemMap.
  nsresult init(const char* filePath, PRIntn flags = PR_RDONLY, PRIntn mode = 0,
                PRFileMapProtect prot = PR_PROT_READONLY);

  // Get the size of the memory mapped file.
  uint32_t size() const {
      MOZ_ASSERT(fileInfo.size <= UINT32_MAX,
                 "Should only call size() if init() succeeded.");
      return uint32_t(fileInfo.size);
  }

  // Get the mapped memory.
  void* address() { MOZ_ASSERT(addr); return addr; }
  const void* address() const { MOZ_ASSERT(addr); return addr; }
};

} // namespace devtools
} // namespace mozilla

#endif // mozilla_devtools_AutoMemMap_h