Index: base/stack_container.h |
diff --git a/base/stack_container.h b/base/stack_container.h |
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-// Copyright (c) 2012 The Chromium Authors. All rights reserved. |
-// Use of this source code is governed by a BSD-style license that can be |
-// found in the LICENSE file. |
- |
-#ifndef BASE_STACK_CONTAINER_H_ |
-#define BASE_STACK_CONTAINER_H_ |
- |
-#include <string> |
-#include <vector> |
- |
-#include "base/basictypes.h" |
-#include "build/build_config.h" |
-#include "base/memory/aligned_memory.h" |
- |
-// This allocator can be used with STL containers to provide a stack buffer |
-// from which to allocate memory and overflows onto the heap. This stack buffer |
-// would be allocated on the stack and allows us to avoid heap operations in |
-// some situations. |
-// |
-// STL likes to make copies of allocators, so the allocator itself can't hold |
-// the data. Instead, we make the creator responsible for creating a |
-// StackAllocator::Source which contains the data. Copying the allocator |
-// merely copies the pointer to this shared source, so all allocators created |
-// based on our allocator will share the same stack buffer. |
-// |
-// This stack buffer implementation is very simple. The first allocation that |
-// fits in the stack buffer will use the stack buffer. Any subsequent |
-// allocations will not use the stack buffer, even if there is unused room. |
-// This makes it appropriate for array-like containers, but the caller should |
-// be sure to reserve() in the container up to the stack buffer size. Otherwise |
-// the container will allocate a small array which will "use up" the stack |
-// buffer. |
-template<typename T, size_t stack_capacity> |
-class StackAllocator : public std::allocator<T> { |
- public: |
- typedef typename std::allocator<T>::pointer pointer; |
- typedef typename std::allocator<T>::size_type size_type; |
- |
- // Backing store for the allocator. The container owner is responsible for |
- // maintaining this for as long as any containers using this allocator are |
- // live. |
- struct Source { |
- Source() : used_stack_buffer_(false) { |
- } |
- |
- // Casts the buffer in its right type. |
- T* stack_buffer() { return stack_buffer_.template data_as<T>(); } |
- const T* stack_buffer() const { |
- return stack_buffer_.template data_as<T>(); |
- } |
- |
- // The buffer itself. It is not of type T because we don't want the |
- // constructors and destructors to be automatically called. Define a POD |
- // buffer of the right size instead. |
- base::AlignedMemory<sizeof(T[stack_capacity]), ALIGNOF(T)> stack_buffer_; |
-#if defined(OS_ANDROID) |
- COMPILE_ASSERT(ALIGNOF(T) <= 16, crbug_115612); |
-#endif |
- |
- // Set when the stack buffer is used for an allocation. We do not track |
- // how much of the buffer is used, only that somebody is using it. |
- bool used_stack_buffer_; |
- }; |
- |
- // Used by containers when they want to refer to an allocator of type U. |
- template<typename U> |
- struct rebind { |
- typedef StackAllocator<U, stack_capacity> other; |
- }; |
- |
- // For the straight up copy c-tor, we can share storage. |
- StackAllocator(const StackAllocator<T, stack_capacity>& rhs) |
- : std::allocator<T>(), source_(rhs.source_) { |
- } |
- |
- // ISO C++ requires the following constructor to be defined, |
- // and std::vector in VC++2008SP1 Release fails with an error |
- // in the class _Container_base_aux_alloc_real (from <xutility>) |
- // if the constructor does not exist. |
- // For this constructor, we cannot share storage; there's |
- // no guarantee that the Source buffer of Ts is large enough |
- // for Us. |
- // TODO: If we were fancy pants, perhaps we could share storage |
- // iff sizeof(T) == sizeof(U). |
- template<typename U, size_t other_capacity> |
- StackAllocator(const StackAllocator<U, other_capacity>& other) |
- : source_(NULL) { |
- } |
- |
- explicit StackAllocator(Source* source) : source_(source) { |
- } |
- |
- // Actually do the allocation. Use the stack buffer if nobody has used it yet |
- // and the size requested fits. Otherwise, fall through to the standard |
- // allocator. |
- pointer allocate(size_type n, void* hint = 0) { |
- if (source_ != NULL && !source_->used_stack_buffer_ |
- && n <= stack_capacity) { |
- source_->used_stack_buffer_ = true; |
- return source_->stack_buffer(); |
- } else { |
- return std::allocator<T>::allocate(n, hint); |
- } |
- } |
- |
- // Free: when trying to free the stack buffer, just mark it as free. For |
- // non-stack-buffer pointers, just fall though to the standard allocator. |
- void deallocate(pointer p, size_type n) { |
- if (source_ != NULL && p == source_->stack_buffer()) |
- source_->used_stack_buffer_ = false; |
- else |
- std::allocator<T>::deallocate(p, n); |
- } |
- |
- private: |
- Source* source_; |
-}; |
- |
-// A wrapper around STL containers that maintains a stack-sized buffer that the |
-// initial capacity of the vector is based on. Growing the container beyond the |
-// stack capacity will transparently overflow onto the heap. The container must |
-// support reserve(). |
-// |
-// WATCH OUT: the ContainerType MUST use the proper StackAllocator for this |
-// type. This object is really intended to be used only internally. You'll want |
-// to use the wrappers below for different types. |
-template<typename TContainerType, int stack_capacity> |
-class StackContainer { |
- public: |
- typedef TContainerType ContainerType; |
- typedef typename ContainerType::value_type ContainedType; |
- typedef StackAllocator<ContainedType, stack_capacity> Allocator; |
- |
- // Allocator must be constructed before the container! |
- StackContainer() : allocator_(&stack_data_), container_(allocator_) { |
- // Make the container use the stack allocation by reserving our buffer size |
- // before doing anything else. |
- container_.reserve(stack_capacity); |
- } |
- |
- // Getters for the actual container. |
- // |
- // Danger: any copies of this made using the copy constructor must have |
- // shorter lifetimes than the source. The copy will share the same allocator |
- // and therefore the same stack buffer as the original. Use std::copy to |
- // copy into a "real" container for longer-lived objects. |
- ContainerType& container() { return container_; } |
- const ContainerType& container() const { return container_; } |
- |
- // Support operator-> to get to the container. This allows nicer syntax like: |
- // StackContainer<...> foo; |
- // std::sort(foo->begin(), foo->end()); |
- ContainerType* operator->() { return &container_; } |
- const ContainerType* operator->() const { return &container_; } |
- |
-#ifdef UNIT_TEST |
- // Retrieves the stack source so that that unit tests can verify that the |
- // buffer is being used properly. |
- const typename Allocator::Source& stack_data() const { |
- return stack_data_; |
- } |
-#endif |
- |
- protected: |
- typename Allocator::Source stack_data_; |
- Allocator allocator_; |
- ContainerType container_; |
- |
- DISALLOW_COPY_AND_ASSIGN(StackContainer); |
-}; |
- |
-// StackString |
-template<size_t stack_capacity> |
-class StackString : public StackContainer< |
- std::basic_string<char, |
- std::char_traits<char>, |
- StackAllocator<char, stack_capacity> >, |
- stack_capacity> { |
- public: |
- StackString() : StackContainer< |
- std::basic_string<char, |
- std::char_traits<char>, |
- StackAllocator<char, stack_capacity> >, |
- stack_capacity>() { |
- } |
- |
- private: |
- DISALLOW_COPY_AND_ASSIGN(StackString); |
-}; |
- |
-// StackWString |
-template<size_t stack_capacity> |
-class StackWString : public StackContainer< |
- std::basic_string<wchar_t, |
- std::char_traits<wchar_t>, |
- StackAllocator<wchar_t, stack_capacity> >, |
- stack_capacity> { |
- public: |
- StackWString() : StackContainer< |
- std::basic_string<wchar_t, |
- std::char_traits<wchar_t>, |
- StackAllocator<wchar_t, stack_capacity> >, |
- stack_capacity>() { |
- } |
- |
- private: |
- DISALLOW_COPY_AND_ASSIGN(StackWString); |
-}; |
- |
-// StackVector |
-// |
-// Example: |
-// StackVector<int, 16> foo; |
-// foo->push_back(22); // we have overloaded operator-> |
-// foo[0] = 10; // as well as operator[] |
-template<typename T, size_t stack_capacity> |
-class StackVector : public StackContainer< |
- std::vector<T, StackAllocator<T, stack_capacity> >, |
- stack_capacity> { |
- public: |
- StackVector() : StackContainer< |
- std::vector<T, StackAllocator<T, stack_capacity> >, |
- stack_capacity>() { |
- } |
- |
- // We need to put this in STL containers sometimes, which requires a copy |
- // constructor. We can't call the regular copy constructor because that will |
- // take the stack buffer from the original. Here, we create an empty object |
- // and make a stack buffer of its own. |
- StackVector(const StackVector<T, stack_capacity>& other) |
- : StackContainer< |
- std::vector<T, StackAllocator<T, stack_capacity> >, |
- stack_capacity>() { |
- this->container().assign(other->begin(), other->end()); |
- } |
- |
- StackVector<T, stack_capacity>& operator=( |
- const StackVector<T, stack_capacity>& other) { |
- this->container().assign(other->begin(), other->end()); |
- return *this; |
- } |
- |
- // Vectors are commonly indexed, which isn't very convenient even with |
- // operator-> (using "->at()" does exception stuff we don't want). |
- T& operator[](size_t i) { return this->container().operator[](i); } |
- const T& operator[](size_t i) const { |
- return this->container().operator[](i); |
- } |
-}; |
- |
-#endif // BASE_STACK_CONTAINER_H_ |