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 //
  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!
  24 class 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_