base/win/scoped_com_initializer.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_WIN_SCOPED_COM_INITIALIZER_H_
   6 #define BASE_WIN_SCOPED_COM_INITIALIZER_H_
   7 #pragma once
   8
   9 #include "base/basictypes.h"
  10 #include "base/logging.h"
  11 #include "build/build_config.h"
  12
  13 #if defined(OS_WIN)
  14
  15 #include <objbase.h>
  16
  17 namespace base {
  18 namespace win {
  19
  20 // Initializes COM in the constructor (STA or MTA), and uninitializes COM in the
  21 // destructor.
  22 class ScopedCOMInitializer {
  23  public:
  24   // Enum value provided to initialize the thread as an MTA instead of STA.
  25   enum SelectMTA { kMTA };
  26
  27   // Constructor for STA initialization.
  28   ScopedCOMInitializer() {
  29     Initialize(COINIT_APARTMENTTHREADED);
  30   }
  31
  32   // Constructor for MTA initialization.
  33   explicit ScopedCOMInitializer(SelectMTA mta) {
  34     Initialize(COINIT_MULTITHREADED);
  35   }
  36
  37   ScopedCOMInitializer::~ScopedCOMInitializer() {
  38 #ifndef NDEBUG
  39     // Using the windows API directly to avoid dependency on platform_thread.
  40     DCHECK_EQ(GetCurrentThreadId(), thread_id_);
  41 #endif
  42     if (SUCCEEDED(hr_))
  43       CoUninitialize();
  44   }
  45
  46   bool succeeded() const { return SUCCEEDED(hr_); }
  47
  48  private:
  49   void Initialize(COINIT init) {
  50 #ifndef NDEBUG
  51     thread_id_ = GetCurrentThreadId();
  52 #endif
  53     hr_ = CoInitializeEx(NULL, init);
  54   }
  55
  56   HRESULT hr_;
  57 #ifndef NDEBUG
  58   // In debug builds we use this variable to catch a potential bug where a
  59   // ScopedCOMInitializer instance is deleted on a different thread than it
  60   // was initially created on.  If that ever happens it can have bad
  61   // consequences and the cause can be tricky to track down.
  62   DWORD thread_id_;
  63 #endif
  64
  65   DISALLOW_COPY_AND_ASSIGN(ScopedCOMInitializer);
  66 };
  67
  68 }  // namespace win
  69 }  // namespace base
  70
  71 #else
  72
  73 namespace base {
  74 namespace win {
  75
  76 // Do-nothing class for other platforms.
  77 class ScopedCOMInitializer {
  78  public:
  79   enum SelectMTA { kMTA };
  80   ScopedCOMInitializer() {}
  81   explicit ScopedCOMInitializer(SelectMTA mta) {}
  82   ~ScopedCOMInitializer() {}
  83
  84   bool succeeded() const { return true; }
  85
  86  private:
  87   DISALLOW_COPY_AND_ASSIGN(ScopedCOMInitializer);
  88 };
  89
  90 }  // namespace win
  91 }  // namespace base
  92
  93 #endif
  94
  95 #endif  // BASE_WIN_SCOPED_COM_INITIALIZER_H_