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      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/logging.h"
     11 #include "base/macros.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_
     80