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1 // Copyright (c) 2010 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2010 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 #ifndef BASE_STACK_CONTAINER_H_ | 5 #ifndef BASE_STACK_CONTAINER_H_ |
6 #define BASE_STACK_CONTAINER_H_ | 6 #define BASE_STACK_CONTAINER_H_ |
7 #pragma once | 7 #pragma once |
8 | 8 |
9 #include <string> | 9 #include <string> |
10 #include <vector> | 10 #include <vector> |
11 | 11 |
12 #include "base/basictypes.h" | 12 #include "base/basictypes.h" |
| 13 #include "base/memory/aligned_memory.h" |
13 | 14 |
14 // This allocator can be used with STL containers to provide a stack buffer | 15 // This allocator can be used with STL containers to provide a stack buffer |
15 // from which to allocate memory and overflows onto the heap. This stack buffer | 16 // from which to allocate memory and overflows onto the heap. This stack buffer |
16 // would be allocated on the stack and allows us to avoid heap operations in | 17 // would be allocated on the stack and allows us to avoid heap operations in |
17 // some situations. | 18 // some situations. |
18 // | 19 // |
19 // STL likes to make copies of allocators, so the allocator itself can't hold | 20 // STL likes to make copies of allocators, so the allocator itself can't hold |
20 // the data. Instead, we make the creator responsible for creating a | 21 // the data. Instead, we make the creator responsible for creating a |
21 // StackAllocator::Source which contains the data. Copying the allocator | 22 // StackAllocator::Source which contains the data. Copying the allocator |
22 // merely copies the pointer to this shared source, so all allocators created | 23 // merely copies the pointer to this shared source, so all allocators created |
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36 typedef typename std::allocator<T>::size_type size_type; | 37 typedef typename std::allocator<T>::size_type size_type; |
37 | 38 |
38 // Backing store for the allocator. The container owner is responsible for | 39 // Backing store for the allocator. The container owner is responsible for |
39 // maintaining this for as long as any containers using this allocator are | 40 // maintaining this for as long as any containers using this allocator are |
40 // live. | 41 // live. |
41 struct Source { | 42 struct Source { |
42 Source() : used_stack_buffer_(false) { | 43 Source() : used_stack_buffer_(false) { |
43 } | 44 } |
44 | 45 |
45 // Casts the buffer in its right type. | 46 // Casts the buffer in its right type. |
46 T* stack_buffer() { return reinterpret_cast<T*>(stack_buffer_); } | 47 T* stack_buffer() { return stack_buffer_.template data_as<T>(); } |
47 const T* stack_buffer() const { | 48 const T* stack_buffer() const { |
48 return reinterpret_cast<const T*>(stack_buffer_); | 49 return stack_buffer_.template data_as<T>(); |
49 } | 50 } |
50 | 51 |
51 // | |
52 // IMPORTANT: Take care to ensure that stack_buffer_ is aligned | |
53 // since it is used to mimic an array of T. | |
54 // Be careful while declaring any unaligned types (like bool) | |
55 // before stack_buffer_. | |
56 // | |
57 | |
58 // The buffer itself. It is not of type T because we don't want the | 52 // The buffer itself. It is not of type T because we don't want the |
59 // constructors and destructors to be automatically called. Define a POD | 53 // constructors and destructors to be automatically called. Define a POD |
60 // buffer of the right size instead. | 54 // buffer of the right size instead. |
61 char stack_buffer_[sizeof(T[stack_capacity])]; | 55 base::AlignedMemory<sizeof(T[stack_capacity]), ALIGNOF(T)> stack_buffer_; |
62 | 56 |
63 // Set when the stack buffer is used for an allocation. We do not track | 57 // Set when the stack buffer is used for an allocation. We do not track |
64 // how much of the buffer is used, only that somebody is using it. | 58 // how much of the buffer is used, only that somebody is using it. |
65 bool used_stack_buffer_; | 59 bool used_stack_buffer_; |
66 }; | 60 }; |
67 | 61 |
68 // Used by containers when they want to refer to an allocator of type U. | 62 // Used by containers when they want to refer to an allocator of type U. |
69 template<typename U> | 63 template<typename U> |
70 struct rebind { | 64 struct rebind { |
71 typedef StackAllocator<U, stack_capacity> other; | 65 typedef StackAllocator<U, stack_capacity> other; |
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245 | 239 |
246 // Vectors are commonly indexed, which isn't very convenient even with | 240 // Vectors are commonly indexed, which isn't very convenient even with |
247 // operator-> (using "->at()" does exception stuff we don't want). | 241 // operator-> (using "->at()" does exception stuff we don't want). |
248 T& operator[](size_t i) { return this->container().operator[](i); } | 242 T& operator[](size_t i) { return this->container().operator[](i); } |
249 const T& operator[](size_t i) const { | 243 const T& operator[](size_t i) const { |
250 return this->container().operator[](i); | 244 return this->container().operator[](i); |
251 } | 245 } |
252 }; | 246 }; |
253 | 247 |
254 #endif // BASE_STACK_CONTAINER_H_ | 248 #endif // BASE_STACK_CONTAINER_H_ |
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