The Tor Browser: comparison ipc/chromium/src/base/stack

--1:000000000000
+:06756b44d82d
+// Copyright (c) 2006-2008 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"
+// 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 reinterpret_cast<T*>(stack_buffer_); }
+const T* stack_buffer() const {
+return reinterpret_cast<const T*>(stack_buffer_);
+}
+//
+// IMPORTANT: Take care to ensure that stack_buffer_ is aligned
+// since it is used to mimic an array of T.
+// Be careful while declaring any unaligned types (like bool)
+// before stack_buffer_.
+//
+// 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.
+char stack_buffer_[sizeof(T[stack_capacity])];
+// 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)
+: 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_EVIL_CONSTRUCTORS(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_EVIL_CONSTRUCTORS(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_EVIL_CONSTRUCTORS(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_

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comparison: ipc/chromium/src/base/stack_container.h

ipc/chromium/src/base/stack_container.h