The Tor Browser: ipc/chromium/src/base/stack_container.h@6474c204b198 (annotated)

ipc/chromium/src/base/stack_container.h@6474c204b198 (annotated)

ipc/chromium/src/base/stack_container.h

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 // 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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ipc/chromium/src/base/stack_container.h@6474c204b198 (annotated)

ipc/chromium/src/base/stack_container.h