Move base to DEPS

base/containers/mru_cache.h

-// Copyright (c) 2011 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.
-
-// This file contains a template for a Most Recently Used cache that allows
-// constant-time access to items using a key, but easy identification of the
-// least-recently-used items for removal.  Each key can only be associated with
-// one payload item at a time.
-//
-// The key object will be stored twice, so it should support efficient copying.
-//
-// NOTE: While all operations are O(1), this code is written for
-// legibility rather than optimality. If future profiling identifies this as
-// a bottleneck, there is room for smaller values of 1 in the O(1). :]
-
-#ifndef BASE_CONTAINERS_MRU_CACHE_H_
-#define BASE_CONTAINERS_MRU_CACHE_H_
-
-#include <list>
-#include <map>
-#include <utility>
-
-#include "base/basictypes.h"
-#include "base/containers/hash_tables.h"
-#include "base/logging.h"
-
-namespace base {
-
-// MRUCacheBase ----------------------------------------------------------------
-
-// This template is used to standardize map type containers that can be used
-// by MRUCacheBase. This level of indirection is necessary because of the way
-// that template template params and default template params interact.
-template <class KeyType, class ValueType>
-struct MRUCacheStandardMap {
-  typedef std::map<KeyType, ValueType> Type;
-};
-
-// Base class for the MRU cache specializations defined below.
-// The deletor will get called on all payloads that are being removed or
-// replaced.
-template <class KeyType, class PayloadType, class DeletorType,
-          template <typename, typename> class MapType = MRUCacheStandardMap>
-class MRUCacheBase {
- public:
-  // The payload of the list. This maintains a copy of the key so we can
-  // efficiently delete things given an element of the list.
-  typedef std::pair<KeyType, PayloadType> value_type;
-
- private:
-  typedef std::list<value_type> PayloadList;
-  typedef typename MapType<KeyType,
-                           typename PayloadList::iterator>::Type KeyIndex;
-
- public:
-  typedef typename PayloadList::size_type size_type;
-
-  typedef typename PayloadList::iterator iterator;
-  typedef typename PayloadList::const_iterator const_iterator;
-  typedef typename PayloadList::reverse_iterator reverse_iterator;
-  typedef typename PayloadList::const_reverse_iterator const_reverse_iterator;
-
-  enum { NO_AUTO_EVICT = 0 };
-
-  // The max_size is the size at which the cache will prune its members to when
-  // a new item is inserted. If the caller wants to manager this itself (for
-  // example, maybe it has special work to do when something is evicted), it
-  // can pass NO_AUTO_EVICT to not restrict the cache size.
-  explicit MRUCacheBase(size_type max_size) : max_size_(max_size) {
-  }
-
-  MRUCacheBase(size_type max_size, const DeletorType& deletor)
-      : max_size_(max_size), deletor_(deletor) {
-  }
-
-  virtual ~MRUCacheBase() {
-    iterator i = begin();
-    while (i != end())
-      i = Erase(i);
-  }
-
-  size_type max_size() const { return max_size_; }
-
-  // Inserts a payload item with the given key. If an existing item has
-  // the same key, it is removed prior to insertion. An iterator indicating the
-  // inserted item will be returned (this will always be the front of the list).
-  //
-  // The payload will be copied. In the case of an OwningMRUCache, this function
-  // will take ownership of the pointer.
-  iterator Put(const KeyType& key, const PayloadType& payload) {
-    // Remove any existing payload with that key.
-    typename KeyIndex::iterator index_iter = index_.find(key);
-    if (index_iter != index_.end()) {
-      // Erase the reference to it. This will call the deletor on the removed
-      // element. The index reference will be replaced in the code below.
-      Erase(index_iter->second);
-    } else if (max_size_ != NO_AUTO_EVICT) {
-      // New item is being inserted which might make it larger than the maximum
-      // size: kick the oldest thing out if necessary.
-      ShrinkToSize(max_size_ - 1);
-    }
-
-    ordering_.push_front(value_type(key, payload));
-    index_.insert(std::make_pair(key, ordering_.begin()));
-    return ordering_.begin();
-  }
-
-  // Retrieves the contents of the given key, or end() if not found. This method
-  // has the side effect of moving the requested item to the front of the
-  // recency list.
-  //
-  // TODO(brettw) We may want a const version of this function in the future.
-  iterator Get(const KeyType& key) {
-    typename KeyIndex::iterator index_iter = index_.find(key);
-    if (index_iter == index_.end())
-      return end();
-    typename PayloadList::iterator iter = index_iter->second;
-
-    // Move the touched item to the front of the recency ordering.
-    ordering_.splice(ordering_.begin(), ordering_, iter);
-    return ordering_.begin();
-  }
-
-  // Retrieves the payload associated with a given key and returns it via
-  // result without affecting the ordering (unlike Get).
-  iterator Peek(const KeyType& key) {
-    typename KeyIndex::const_iterator index_iter = index_.find(key);
-    if (index_iter == index_.end())
-      return end();
-    return index_iter->second;
-  }
-
-  const_iterator Peek(const KeyType& key) const {
-    typename KeyIndex::const_iterator index_iter = index_.find(key);
-    if (index_iter == index_.end())
-      return end();
-    return index_iter->second;
-  }
-
-  // Erases the item referenced by the given iterator. An iterator to the item
-  // following it will be returned. The iterator must be valid.
-  iterator Erase(iterator pos) {
-    deletor_(pos->second);
-    index_.erase(pos->first);
-    return ordering_.erase(pos);
-  }
-
-  // MRUCache entries are often processed in reverse order, so we add this
-  // convenience function (not typically defined by STL containers).
-  reverse_iterator Erase(reverse_iterator pos) {
-    // We have to actually give it the incremented iterator to delete, since
-    // the forward iterator that base() returns is actually one past the item
-    // being iterated over.
-    return reverse_iterator(Erase((++pos).base()));
-  }
-
-  // Shrinks the cache so it only holds |new_size| items. If |new_size| is
-  // bigger or equal to the current number of items, this will do nothing.
-  void ShrinkToSize(size_type new_size) {
-    for (size_type i = size(); i > new_size; i--)
-      Erase(rbegin());
-  }
-
-  // Deletes everything from the cache.
-  void Clear() {
-    for (typename PayloadList::iterator i(ordering_.begin());
-         i != ordering_.end(); ++i)
-      deletor_(i->second);
-    index_.clear();
-    ordering_.clear();
-  }
-
-  // Returns the number of elements in the cache.
-  size_type size() const {
-    // We don't use ordering_.size() for the return value because
-    // (as a linked list) it can be O(n).
-    DCHECK(index_.size() == ordering_.size());
-    return index_.size();
-  }
-
-  // Allows iteration over the list. Forward iteration starts with the most
-  // recent item and works backwards.
-  //
-  // Note that since these iterators are actually iterators over a list, you
-  // can keep them as you insert or delete things (as long as you don't delete
-  // the one you are pointing to) and they will still be valid.
-  iterator begin() { return ordering_.begin(); }
-  const_iterator begin() const { return ordering_.begin(); }
-  iterator end() { return ordering_.end(); }
-  const_iterator end() const { return ordering_.end(); }
-
-  reverse_iterator rbegin() { return ordering_.rbegin(); }
-  const_reverse_iterator rbegin() const { return ordering_.rbegin(); }
-  reverse_iterator rend() { return ordering_.rend(); }
-  const_reverse_iterator rend() const { return ordering_.rend(); }
-
-  bool empty() const { return ordering_.empty(); }
-
- private:
-  PayloadList ordering_;
-  KeyIndex index_;
-
-  size_type max_size_;
-
-  DeletorType deletor_;
-
-  DISALLOW_COPY_AND_ASSIGN(MRUCacheBase);
-};
-
-// MRUCache --------------------------------------------------------------------
-
-// A functor that does nothing. Used by the MRUCache.
-template<class PayloadType>
-class MRUCacheNullDeletor {
- public:
-  void operator()(const PayloadType& payload) {}
-};
-
-// A container that does not do anything to free its data. Use this when storing
-// value types (as opposed to pointers) in the list.
-template <class KeyType, class PayloadType>
-class MRUCache : public MRUCacheBase<KeyType,
-                                     PayloadType,
-                                     MRUCacheNullDeletor<PayloadType> > {
- private:
-  typedef MRUCacheBase<KeyType, PayloadType,
-      MRUCacheNullDeletor<PayloadType> > ParentType;
-
- public:
-  // See MRUCacheBase, noting the possibility of using NO_AUTO_EVICT.
-  explicit MRUCache(typename ParentType::size_type max_size)
-      : ParentType(max_size) {
-  }
-  virtual ~MRUCache() {
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(MRUCache);
-};
-
-// OwningMRUCache --------------------------------------------------------------
-
-template<class PayloadType>
-class MRUCachePointerDeletor {
- public:
-  void operator()(const PayloadType& payload) { delete payload; }
-};
-
-// A cache that owns the payload type, which must be a non-const pointer type.
-// The pointers will be deleted when they are removed, replaced, or when the
-// cache is destroyed.
-template <class KeyType, class PayloadType>
-class OwningMRUCache
-    : public MRUCacheBase<KeyType,
-                          PayloadType,
-                          MRUCachePointerDeletor<PayloadType> > {
- private:
-  typedef MRUCacheBase<KeyType, PayloadType,
-      MRUCachePointerDeletor<PayloadType> > ParentType;
-
- public:
-  // See MRUCacheBase, noting the possibility of using NO_AUTO_EVICT.
-  explicit OwningMRUCache(typename ParentType::size_type max_size)
-      : ParentType(max_size) {
-  }
-  virtual ~OwningMRUCache() {
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(OwningMRUCache);
-};
-
-// HashingMRUCache ------------------------------------------------------------
-
-template <class KeyType, class ValueType>
-struct MRUCacheHashMap {
-  typedef base::hash_map<KeyType, ValueType> Type;
-};
-
-// This class is similar to MRUCache, except that it uses base::hash_map as
-// the map type instead of std::map. Note that your KeyType must be hashable
-// to use this cache.
-template <class KeyType, class PayloadType>
-class HashingMRUCache : public MRUCacheBase<KeyType,
-                                            PayloadType,
-                                            MRUCacheNullDeletor<PayloadType>,
-                                            MRUCacheHashMap> {
- private:
-  typedef MRUCacheBase<KeyType, PayloadType,
-                       MRUCacheNullDeletor<PayloadType>,
-                       MRUCacheHashMap> ParentType;
-
- public:
-  // See MRUCacheBase, noting the possibility of using NO_AUTO_EVICT.
-  explicit HashingMRUCache(typename ParentType::size_type max_size)
-      : ParentType(max_size) {
-  }
-  virtual ~HashingMRUCache() {
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(HashingMRUCache);
-};
-
-}  // namespace base
-
-#endif  // BASE_CONTAINERS_MRU_CACHE_H_