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
14namespace base {
15namespace win {
16
17// Initializes COM in the constructor (STA or MTA), and uninitializes COM in the
18// destructor.
19//
20// WARNING: This should only be used once per thread, ideally scoped to a
21// similar lifetime as the thread itself.  You should not be using this in
22// random utility functions that make COM calls -- instead ensure these
23// functions are running on a COM-supporting thread!
24class ScopedCOMInitializer {
25 public:
26  // Enum value provided to initialize the thread as an MTA instead of STA.
27  enum SelectMTA { kMTA };
28
29  // Constructor for STA initialization.
30  ScopedCOMInitializer() {
31    Initialize(COINIT_APARTMENTTHREADED);
32  }
33
34  // Constructor for MTA initialization.
35  explicit ScopedCOMInitializer(SelectMTA mta) {
36    Initialize(COINIT_MULTITHREADED);
37  }
38
39  ~ScopedCOMInitializer() {
40#ifndef NDEBUG
41    // Using the windows API directly to avoid dependency on platform_thread.
42    DCHECK_EQ(GetCurrentThreadId(), thread_id_);
43#endif
44    if (succeeded())
45      CoUninitialize();
46  }
47
48  bool succeeded() const { return SUCCEEDED(hr_); }
49
50 private:
51  void Initialize(COINIT init) {
52#ifndef NDEBUG
53    thread_id_ = GetCurrentThreadId();
54#endif
55    hr_ = CoInitializeEx(NULL, init);
56#ifndef NDEBUG
57    if (hr_ == S_FALSE)
58      LOG(ERROR) << "Multiple CoInitialize() calls for thread " << thread_id_;
59    else
60      DCHECK_NE(RPC_E_CHANGED_MODE, hr_) << "Invalid COM thread model change";
61#endif
62  }
63
64  HRESULT hr_;
65#ifndef NDEBUG
66  // In debug builds we use this variable to catch a potential bug where a
67  // ScopedCOMInitializer instance is deleted on a different thread than it
68  // was initially created on.  If that ever happens it can have bad
69  // consequences and the cause can be tricky to track down.
70  DWORD thread_id_;
71#endif
72
73  DISALLOW_COPY_AND_ASSIGN(ScopedCOMInitializer);
74};
75
76}  // namespace win
77}  // namespace base
78
79#endif  // BASE_WIN_SCOPED_COM_INITIALIZER_H_
80