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Side by Side Diff: base/memory/scoped_ptr.h

Issue 1358373002: Change scoped_ptr::reset()'s behaviour to match unique_ptr. (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: Expand comment. Created 5 years, 3 months ago
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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 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 2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file. 3 // found in the LICENSE file.
4 4
5 // Scopers help you manage ownership of a pointer, helping you easily manage a 5 // Scopers help you manage ownership of a pointer, helping you easily manage a
6 // pointer within a scope, and automatically destroying the pointer at the end 6 // pointer within a scope, and automatically destroying the pointer at the end
7 // of a scope. There are two main classes you will use, which correspond to the 7 // of a scope. There are two main classes you will use, which correspond to the
8 // operators new/delete and new[]/delete[]. 8 // operators new/delete and new[]/delete[].
9 // 9 //
10 // Example usage (scoped_ptr<T>): 10 // Example usage (scoped_ptr<T>):
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221 // builds. 221 // builds.
222 static_cast<D&>(data_)(data_.ptr); 222 static_cast<D&>(data_)(data_.ptr);
223 } 223 }
224 } 224 }
225 225
226 void reset(T* p) { 226 void reset(T* p) {
227 // This is a self-reset, which is no longer allowed for default deleters: 227 // This is a self-reset, which is no longer allowed for default deleters:
228 // https://crbug.com/162971 228 // https://crbug.com/162971
229 assert(!ShouldAbortOnSelfReset<D>::value || p == nullptr || p != data_.ptr); 229 assert(!ShouldAbortOnSelfReset<D>::value || p == nullptr || p != data_.ptr);
230 230
231 // Note that running data_.ptr = p can lead to undefined behavior if 231 // Match C++11's definition of unique_ptr::reset(), which requires changing
232 // get_deleter()(get()) deletes this. In order to prevent this, reset() 232 // the pointer before invoking the deleter on the old pointer. This prevents
233 // should update the stored pointer before deleting its old value. 233 // |this| from being accessed after the deleter is run, which may destroy
234 // 234 // |this|.
235 // However, changing reset() to use that behavior may cause current code to
236 // break in unexpected ways. If the destruction of the owned object
237 // dereferences the scoped_ptr when it is destroyed by a call to reset(),
238 // then it will incorrectly dispatch calls to |p| rather than the original
239 // value of |data_.ptr|.
240 //
241 // During the transition period, set the stored pointer to nullptr while
242 // deleting the object. Eventually, this safety check will be removed to
243 // prevent the scenario initially described from occuring and
244 // http://crbug.com/176091 can be closed.
245 T* old = data_.ptr; 235 T* old = data_.ptr;
246 data_.ptr = nullptr; 236 data_.ptr = p;
247 if (old != nullptr) 237 if (old != nullptr)
248 static_cast<D&>(data_)(old); 238 static_cast<D&>(data_)(old);
249 data_.ptr = p;
250 } 239 }
251 240
252 T* get() const { return data_.ptr; } 241 T* get() const { return data_.ptr; }
253 242
254 D& get_deleter() { return data_; } 243 D& get_deleter() { return data_; }
255 const D& get_deleter() const { return data_; } 244 const D& get_deleter() const { return data_; }
256 245
257 void swap(scoped_ptr_impl& p2) { 246 void swap(scoped_ptr_impl& p2) {
258 // Standard swap idiom: 'using std::swap' ensures that std::swap is 247 // Standard swap idiom: 'using std::swap' ensures that std::swap is
259 // present in the overload set, but we call swap unqualified so that 248 // present in the overload set, but we call swap unqualified so that
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583 scoped_ptr<T> make_scoped_ptr(T* ptr) { 572 scoped_ptr<T> make_scoped_ptr(T* ptr) {
584 return scoped_ptr<T>(ptr); 573 return scoped_ptr<T>(ptr);
585 } 574 }
586 575
587 template <typename T> 576 template <typename T>
588 std::ostream& operator<<(std::ostream& out, const scoped_ptr<T>& p) { 577 std::ostream& operator<<(std::ostream& out, const scoped_ptr<T>& p) {
589 return out << p.get(); 578 return out << p.get();
590 } 579 }
591 580
592 #endif // BASE_MEMORY_SCOPED_PTR_H_ 581 #endif // BASE_MEMORY_SCOPED_PTR_H_
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