base/win/scoped_com_initializer.h

   1 // Copyright (c) 2012 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
   8 #include <objbase.h>
   9
  10 #include "base/basictypes.h"
  11 #include "base/logging.h"
  12 #include "build/build_config.h"
  13
  14 namespace base {
  15 namespace win {
  16
  17 // Initializes COM in the constructor (STA or MTA), and uninitializes COM in the
  18 // destructor.
  19 class ScopedCOMInitializer {
  20  public:
  21   // Enum value provided to initialize the thread as an MTA instead of STA.
  22   enum SelectMTA { kMTA };
  23
  24   // Constructor for STA initialization.
  25   ScopedCOMInitializer() {
  26     Initialize(COINIT_APARTMENTTHREADED);
  27   }
  28
  29   // Constructor for MTA initialization.
  30   explicit ScopedCOMInitializer(SelectMTA mta) {
  31     Initialize(COINIT_MULTITHREADED);
  32   }
  33
  34   ~ScopedCOMInitializer() {
  35 #ifndef NDEBUG
  36     // Using the windows API directly to avoid dependency on platform_thread.
  37     DCHECK_EQ(GetCurrentThreadId(), thread_id_);
  38 #endif
  39     if (succeeded())
  40       CoUninitialize();
  41   }
  42
  43   bool succeeded() const { return SUCCEEDED(hr_); }
  44
  45  private:
  46   void Initialize(COINIT init) {
  47 #ifndef NDEBUG
  48     thread_id_ = GetCurrentThreadId();
  49 #endif
  50     hr_ = CoInitializeEx(NULL, init);
  51 #ifndef NDEBUG
  52     if (hr_ == S_FALSE)
  53       LOG(ERROR) << "Multiple CoInitialize() calls for thread " << thread_id_;
  54     else
  55       DCHECK_NE(RPC_E_CHANGED_MODE, hr_) << "Invalid COM thread model change";
  56 #endif
  57   }
  58
  59   HRESULT hr_;
  60 #ifndef NDEBUG
  61   // In debug builds we use this variable to catch a potential bug where a
  62   // ScopedCOMInitializer instance is deleted on a different thread than it
  63   // was initially created on.  If that ever happens it can have bad
  64   // consequences and the cause can be tricky to track down.
  65   DWORD thread_id_;
  66 #endif
  67
  68   DISALLOW_COPY_AND_ASSIGN(ScopedCOMInitializer);
  69 };
  70
  71 }  // namespace win
  72 }  // namespace base
  73
  74 #endif  // BASE_WIN_SCOPED_COM_INITIALIZER_H_