net/disk_cache/mem_entry_impl.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef NET_DISK_CACHE_MEM_ENTRY_IMPL_H_
   6 #define NET_DISK_CACHE_MEM_ENTRY_IMPL_H_
   7
   8 #include "base/containers/hash_tables.h"
   9 #include "base/gtest_prod_util.h"
  10 #include "base/memory/scoped_ptr.h"
  11 #include "net/base/net_log.h"
  12 #include "net/disk_cache/disk_cache.h"
  13
  14 namespace disk_cache {
  15
  16 class MemBackendImpl;
  17
  18 // This class implements the Entry interface for the memory-only cache. An
  19 // object of this class represents a single entry on the cache. We use two
  20 // types of entries, parent and child to support sparse caching.
  21 //
  22 // A parent entry is non-sparse until a sparse method is invoked (i.e.
  23 // ReadSparseData, WriteSparseData, GetAvailableRange) when sparse information
  24 // is initialized. It then manages a list of child entries and delegates the
  25 // sparse API calls to the child entries. It creates and deletes child entries
  26 // and updates the list when needed.
  27 //
  28 // A child entry is used to carry partial cache content, non-sparse methods like
  29 // ReadData and WriteData cannot be applied to them. The lifetime of a child
  30 // entry is managed by the parent entry that created it except that the entry
  31 // can be evicted independently. A child entry does not have a key and it is not
  32 // registered in the backend's entry map. It is registered in the backend's
  33 // ranking list to enable eviction of a partial content.
  34 //
  35 // A sparse entry has a fixed maximum size and can be partially filled. There
  36 // can only be one continous filled region in a sparse entry, as illustrated by
  37 // the following example:
  38 // | xxx ooooo |
  39 // x = unfilled region
  40 // o = filled region
  41 // It is guranteed that there is at most one unfilled region and one filled
  42 // region, and the unfilled region (if there is one) is always before the filled
  43 // region. The book keeping for filled region in a sparse entry is done by using
  44 // the variable |child_first_pos_| (inclusive).
  45
  46 class MemEntryImpl : public Entry {
  47  public:
  48   enum EntryType {
  49     kParentEntry,
  50     kChildEntry,
  51   };
  52
  53   explicit MemEntryImpl(MemBackendImpl* backend);
  54
  55   // Performs the initialization of a EntryImpl that will be added to the
  56   // cache.
  57   bool CreateEntry(const std::string& key, net::NetLog* net_log);
  58
  59   // Permanently destroys this entry.
  60   void InternalDoom();
  61
  62   void Open();
  63   bool InUse();
  64
  65   MemEntryImpl* next() const {
  66     return next_;
  67   }
  68
  69   MemEntryImpl* prev() const {
  70     return prev_;
  71   }
  72
  73   void set_next(MemEntryImpl* next) {
  74     next_ = next;
  75   }
  76
  77   void set_prev(MemEntryImpl* prev) {
  78     prev_ = prev;
  79   }
  80
  81   EntryType type() const {
  82     return parent_ ? kChildEntry : kParentEntry;
  83   }
  84
  85   const net::BoundNetLog& net_log() {
  86     return net_log_;
  87   }
  88
  89   // Entry interface.
  90   virtual void Doom() OVERRIDE;
  91   virtual void Close() OVERRIDE;
  92   virtual std::string GetKey() const OVERRIDE;
  93   virtual base::Time GetLastUsed() const OVERRIDE;
  94   virtual base::Time GetLastModified() const OVERRIDE;
  95   virtual int32 GetDataSize(int index) const OVERRIDE;
  96   virtual int ReadData(int index, int offset, IOBuffer* buf, int buf_len,
  97                        const CompletionCallback& callback) OVERRIDE;
  98   virtual int WriteData(int index, int offset, IOBuffer* buf, int buf_len,
  99                         const CompletionCallback& callback,
 100                         bool truncate) OVERRIDE;
 101   virtual int ReadSparseData(int64 offset, IOBuffer* buf, int buf_len,
 102                              const CompletionCallback& callback) OVERRIDE;
 103   virtual int WriteSparseData(int64 offset, IOBuffer* buf, int buf_len,
 104                               const CompletionCallback& callback) OVERRIDE;
 105   virtual int GetAvailableRange(int64 offset, int len, int64* start,
 106                                 const CompletionCallback& callback) OVERRIDE;
 107   virtual bool CouldBeSparse() const OVERRIDE;
 108   virtual void CancelSparseIO() OVERRIDE {}
 109   virtual int ReadyForSparseIO(const CompletionCallback& callback) OVERRIDE;
 110
 111  private:
 112   typedef base::hash_map<int, MemEntryImpl*> EntryMap;
 113
 114   enum {
 115     NUM_STREAMS = 3
 116   };
 117
 118   virtual ~MemEntryImpl();
 119
 120   // Do all the work for corresponding public functions.  Implemented as
 121   // separate functions to make logging of results simpler.
 122   int InternalReadData(int index, int offset, IOBuffer* buf, int buf_len);
 123   int InternalWriteData(int index, int offset, IOBuffer* buf, int buf_len,
 124                         bool truncate);
 125   int InternalReadSparseData(int64 offset, IOBuffer* buf, int buf_len);
 126   int InternalWriteSparseData(int64 offset, IOBuffer* buf, int buf_len);
 127
 128   // Old Entry interface.
 129   int GetAvailableRange(int64 offset, int len, int64* start);
 130
 131   // Grows and cleans up the data buffer.
 132   void PrepareTarget(int index, int offset, int buf_len);
 133
 134   // Updates ranking information.
 135   void UpdateRank(bool modified);
 136
 137   // Initializes the children map and sparse info. This method is only called
 138   // on a parent entry.
 139   bool InitSparseInfo();
 140
 141   // Performs the initialization of a MemEntryImpl as a child entry.
 142   // |parent| is the pointer to the parent entry. |child_id| is the ID of
 143   // the new child.
 144   bool InitChildEntry(MemEntryImpl* parent, int child_id, net::NetLog* net_log);
 145
 146   // Returns an entry responsible for |offset|. The returned entry can be a
 147   // child entry or this entry itself if |offset| points to the first range.
 148   // If such entry does not exist and |create| is true, a new child entry is
 149   // created.
 150   MemEntryImpl* OpenChild(int64 offset, bool create);
 151
 152   // Finds the first child located within the range [|offset|, |offset + len|).
 153   // Returns the number of bytes ahead of |offset| to reach the first available
 154   // bytes in the entry. The first child found is output to |child|.
 155   int FindNextChild(int64 offset, int len, MemEntryImpl** child);
 156
 157   // Removes child indexed by |child_id| from the children map.
 158   void DetachChild(int child_id);
 159
 160   std::string key_;
 161   std::vector<char> data_[NUM_STREAMS];  // User data.
 162   int32 data_size_[NUM_STREAMS];
 163   int ref_count_;
 164
 165   int child_id_;              // The ID of a child entry.
 166   int child_first_pos_;       // The position of the first byte in a child
 167                               // entry.
 168   MemEntryImpl* next_;        // Pointers for the LRU list.
 169   MemEntryImpl* prev_;
 170   MemEntryImpl* parent_;      // Pointer to the parent entry.
 171   scoped_ptr<EntryMap> children_;
 172
 173   base::Time last_modified_;  // LRU information.
 174   base::Time last_used_;
 175   MemBackendImpl* backend_;   // Back pointer to the cache.
 176   bool doomed_;               // True if this entry was removed from the cache.
 177
 178   net::BoundNetLog net_log_;
 179
 180   DISALLOW_COPY_AND_ASSIGN(MemEntryImpl);
 181 };
 182
 183 }  // namespace disk_cache
 184
 185 #endif  // NET_DISK_CACHE_MEM_ENTRY_IMPL_H_