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| 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_COMPTR_H_ | |
| 6 #define BASE_WIN_SCOPED_COMPTR_H_ | |
| 7 | |
| 8 #include <unknwn.h> | |
| 9 | |
| 10 #include "base/logging.h" | |
| 11 #include "base/memory/ref_counted.h" | |
| 12 | |
| 13 namespace base { | |
| 14 namespace win { | |
| 15 | |
| 16 // A fairly minimalistic smart class for COM interface pointers. | |
| 17 // Uses scoped_refptr for the basic smart pointer functionality | |
| 18 // and adds a few IUnknown specific services. | |
| 19 template <class Interface, const IID* interface_id = &__uuidof(Interface)> | |
| 20 class ScopedComPtr : public scoped_refptr<Interface> { | |
| 21 public: | |
| 22 // Utility template to prevent users of ScopedComPtr from calling AddRef | |
| 23 // and/or Release() without going through the ScopedComPtr class. | |
| 24 class BlockIUnknownMethods : public Interface { | |
| 25 private: | |
| 26 STDMETHOD(QueryInterface)(REFIID iid, void** object) = 0; | |
| 27 STDMETHOD_(ULONG, AddRef)() = 0; | |
| 28 STDMETHOD_(ULONG, Release)() = 0; | |
| 29 }; | |
| 30 | |
| 31 typedef scoped_refptr<Interface> ParentClass; | |
| 32 | |
| 33 ScopedComPtr() { | |
| 34 } | |
| 35 | |
| 36 explicit ScopedComPtr(Interface* p) : ParentClass(p) { | |
| 37 } | |
| 38 | |
| 39 ScopedComPtr(const ScopedComPtr<Interface, interface_id>& p) | |
| 40 : ParentClass(p) { | |
| 41 } | |
| 42 | |
| 43 ~ScopedComPtr() { | |
| 44 // We don't want the smart pointer class to be bigger than the pointer | |
| 45 // it wraps. | |
| 46 COMPILE_ASSERT(sizeof(ScopedComPtr<Interface, interface_id>) == | |
| 47 sizeof(Interface*), ScopedComPtrSize); | |
| 48 } | |
| 49 | |
| 50 // Explicit Release() of the held object. Useful for reuse of the | |
| 51 // ScopedComPtr instance. | |
| 52 // Note that this function equates to IUnknown::Release and should not | |
| 53 // be confused with e.g. scoped_ptr::release(). | |
| 54 void Release() { | |
| 55 if (ptr_ != NULL) { | |
| 56 ptr_->Release(); | |
| 57 ptr_ = NULL; | |
| 58 } | |
| 59 } | |
| 60 | |
| 61 // Sets the internal pointer to NULL and returns the held object without | |
| 62 // releasing the reference. | |
| 63 Interface* Detach() { | |
| 64 Interface* p = ptr_; | |
| 65 ptr_ = NULL; | |
| 66 return p; | |
| 67 } | |
| 68 | |
| 69 // Accepts an interface pointer that has already been addref-ed. | |
| 70 void Attach(Interface* p) { | |
| 71 DCHECK(!ptr_); | |
| 72 ptr_ = p; | |
| 73 } | |
| 74 | |
| 75 // Retrieves the pointer address. | |
| 76 // Used to receive object pointers as out arguments (and take ownership). | |
| 77 // The function DCHECKs on the current value being NULL. | |
| 78 // Usage: Foo(p.Receive()); | |
| 79 Interface** Receive() { | |
| 80 DCHECK(!ptr_) << "Object leak. Pointer must be NULL"; | |
| 81 return &ptr_; | |
| 82 } | |
| 83 | |
| 84 // A convenience for whenever a void pointer is needed as an out argument. | |
| 85 void** ReceiveVoid() { | |
| 86 return reinterpret_cast<void**>(Receive()); | |
| 87 } | |
| 88 | |
| 89 template <class Query> | |
| 90 HRESULT QueryInterface(Query** p) { | |
| 91 DCHECK(p != NULL); | |
| 92 DCHECK(ptr_ != NULL); | |
| 93 // IUnknown already has a template version of QueryInterface | |
| 94 // so the iid parameter is implicit here. The only thing this | |
| 95 // function adds are the DCHECKs. | |
| 96 return ptr_->QueryInterface(p); | |
| 97 } | |
| 98 | |
| 99 // QI for times when the IID is not associated with the type. | |
| 100 HRESULT QueryInterface(const IID& iid, void** obj) { | |
| 101 DCHECK(obj != NULL); | |
| 102 DCHECK(ptr_ != NULL); | |
| 103 return ptr_->QueryInterface(iid, obj); | |
| 104 } | |
| 105 | |
| 106 // Queries |other| for the interface this object wraps and returns the | |
| 107 // error code from the other->QueryInterface operation. | |
| 108 HRESULT QueryFrom(IUnknown* object) { | |
| 109 DCHECK(object != NULL); | |
| 110 return object->QueryInterface(Receive()); | |
| 111 } | |
| 112 | |
| 113 // Convenience wrapper around CoCreateInstance | |
| 114 HRESULT CreateInstance(const CLSID& clsid, IUnknown* outer = NULL, | |
| 115 DWORD context = CLSCTX_ALL) { | |
| 116 DCHECK(!ptr_); | |
| 117 HRESULT hr = ::CoCreateInstance(clsid, outer, context, *interface_id, | |
| 118 reinterpret_cast<void**>(&ptr_)); | |
| 119 return hr; | |
| 120 } | |
| 121 | |
| 122 // Checks if the identity of |other| and this object is the same. | |
| 123 bool IsSameObject(IUnknown* other) { | |
| 124 if (!other && !ptr_) | |
| 125 return true; | |
| 126 | |
| 127 if (!other || !ptr_) | |
| 128 return false; | |
| 129 | |
| 130 ScopedComPtr<IUnknown> my_identity; | |
| 131 QueryInterface(my_identity.Receive()); | |
| 132 | |
| 133 ScopedComPtr<IUnknown> other_identity; | |
| 134 other->QueryInterface(other_identity.Receive()); | |
| 135 | |
| 136 return my_identity == other_identity; | |
| 137 } | |
| 138 | |
| 139 // Provides direct access to the interface. | |
| 140 // Here we use a well known trick to make sure we block access to | |
| 141 // IUnknown methods so that something bad like this doesn't happen: | |
| 142 // ScopedComPtr<IUnknown> p(Foo()); | |
| 143 // p->Release(); | |
| 144 // ... later the destructor runs, which will Release() again. | |
| 145 // and to get the benefit of the DCHECKs we add to QueryInterface. | |
| 146 // There's still a way to call these methods if you absolutely must | |
| 147 // by statically casting the ScopedComPtr instance to the wrapped interface | |
| 148 // and then making the call... but generally that shouldn't be necessary. | |
| 149 BlockIUnknownMethods* operator->() const { | |
| 150 DCHECK(ptr_ != NULL); | |
| 151 return reinterpret_cast<BlockIUnknownMethods*>(ptr_); | |
| 152 } | |
| 153 | |
| 154 // Pull in operator=() from the parent class. | |
| 155 using scoped_refptr<Interface>::operator=; | |
| 156 | |
| 157 // static methods | |
| 158 | |
| 159 static const IID& iid() { | |
| 160 return *interface_id; | |
| 161 } | |
| 162 }; | |
| 163 | |
| 164 } // namespace win | |
| 165 } // namespace base | |
| 166 | |
| 167 #endif // BASE_WIN_SCOPED_COMPTR_H_ | |
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