dom/ipc/MemMapSnapshot.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef dom_ipc_MemMapSnapshot_h
   8 #define dom_ipc_MemMapSnapshot_h
   9
  10 #include "mozilla/Attributes.h"
  11 #include "mozilla/Maybe.h"
  12 #include "mozilla/RangedPtr.h"
  13 #include "mozilla/Result.h"
  14 #include "base/shared_memory.h"
  15 #include "ErrorList.h"
  16
  17 namespace mozilla {
  18 namespace loader {
  19 class AutoMemMap;
  20 }
  21
  22 namespace ipc {
  23
  24 /**
  25  * A helper class for creating a read-only snapshot of memory-mapped data.
  26  *
  27  * The Init() method initializes a read-write memory mapped region of the given
  28  * size, which can be initialized with arbitrary data. The Finalize() method
  29  * remaps that region as read-only (and backs it with a read-only file
  30  * descriptor), and initializes an AutoMemMap with the new contents.
  31  *
  32  * The file descriptor for the resulting AutoMemMap can be shared among
  33  * processes, to safely access a shared, read-only copy of the data snapshot.
  34  */
  35 class MOZ_RAII MemMapSnapshot {
  36  public:
  37   Result<Ok, nsresult> Init(size_t aSize);
  38   Result<Ok, nsresult> Finalize(loader::AutoMemMap& aMap);
  39
  40   template <typename T>
  41   RangedPtr<T> Get() {
  42     MOZ_ASSERT(mInitialized);
  43     return {static_cast<T*>(mMem.memory()), mMem.max_size() / sizeof(T)};
  44   }
  45
  46  private:
  47   base::SharedMemory mMem;
  48   bool mInitialized = false;
  49 };
  50
  51 }  // namespace ipc
  52 }  // namespace mozilla
  53
  54 #endif  // dom_ipc_MemMapSnapshot_h