Reland: Refactor and shorten in-memory cache.

net/disk_cache/memory/mem_entry_impl.h

Index: net/disk_cache/memory/mem_entry_impl.h
diff --git a/net/disk_cache/memory/mem_entry_impl.h b/net/disk_cache/memory/mem_entry_impl.h
index 52a1696f63c457be200f402ef5c1ed2c336ab6e3..11634e6ab9a883a64856f31d5e459b65707eb36f 100644
--- a/net/disk_cache/memory/mem_entry_impl.h
+++ b/net/disk_cache/memory/mem_entry_impl.h
@@ -7,9 +7,15 @@
 
 #include <stdint.h>
 
+#include <string>
+#include <vector>
+
 #include "base/containers/hash_tables.h"
+#include "base/containers/linked_list.h"
+#include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
 #include "net/disk_cache/disk_cache.h"
 #include "net/log/net_log.h"
 
@@ -18,8 +24,8 @@ namespace disk_cache {
 class MemBackendImpl;
 
 // This class implements the Entry interface for the memory-only cache. An
-// object of this class represents a single entry on the cache. We use two
-// types of entries, parent and child to support sparse caching.
+// object of this class represents a single entry on the cache. We use two types
+// of entries, parent and child to support sparse caching.
 //
 // A parent entry is non-sparse until a sparse method is invoked (i.e.
 // ReadSparseData, WriteSparseData, GetAvailableRange) when sparse information
@@ -31,64 +37,62 @@ class MemBackendImpl;
 // ReadData and WriteData cannot be applied to them. The lifetime of a child
 // entry is managed by the parent entry that created it except that the entry
 // can be evicted independently. A child entry does not have a key and it is not
-// registered in the backend's entry map. It is registered in the backend's
-// ranking list to enable eviction of a partial content.
+// registered in the backend's entry map.
 //
-// A sparse entry has a fixed maximum size and can be partially filled. There
-// can only be one continous filled region in a sparse entry, as illustrated by
-// the following example:
+// A sparse child entry has a fixed maximum size and can be partially
+// filled. There can only be one continous filled region in a sparse entry, as
+// illustrated by the following example:
 // | xxx ooooo |
 // x = unfilled region
 // o = filled region
-// It is guranteed that there is at most one unfilled region and one filled
+// It is guaranteed that there is at most one unfilled region and one filled
 // region, and the unfilled region (if there is one) is always before the filled
 // region. The book keeping for filled region in a sparse entry is done by using
-// the variable |child_first_pos_| (inclusive).
+// the variable |child_first_pos_|.
 
-class MemEntryImpl : public Entry {
+class NET_EXPORT_PRIVATE MemEntryImpl final
+    : public Entry,
+      public base::LinkNode<MemEntryImpl> {
  public:
   enum EntryType {
-    kParentEntry,
-    kChildEntry,
+    PARENT_ENTRY,
+    CHILD_ENTRY,
   };
 
-  explicit MemEntryImpl(MemBackendImpl* backend);
+  // Provided to better document calls to |UpdateStateOnUse()|.
+  enum EntryModified {
+    ENTRY_WAS_NOT_MODIFIED,
+    ENTRY_WAS_MODIFIED,
+  };
 
-  // Performs the initialization of a EntryImpl that will be added to the
-  // cache.
-  bool CreateEntry(const std::string& key, net::NetLog* net_log);
+  // Constructor for parent entries.
+  MemEntryImpl(MemBackendImpl* backend,
+               const std::string& key,
+               net::NetLog* net_log);
 
-  // Permanently destroys this entry.
-  void InternalDoom();
+  // Constructor for child entries.
+  MemEntryImpl(MemBackendImpl* backend,
+               int child_id,
+               MemEntryImpl* parent,
+               net::NetLog* net_log);
 
   void Open();
-  bool InUse();
-
-  MemEntryImpl* next() const {
-    return next_;
-  }
+  bool InUse() const;
 
-  MemEntryImpl* prev() const {
-    return prev_;
-  }
+  EntryType type() const { return parent_ ? CHILD_ENTRY : PARENT_ENTRY; }
+  const std::string& key() const { return key_; }
+  const MemEntryImpl* parent() const { return parent_; }
+  int child_id() const { return child_id_; }
+  base::Time last_used() const { return last_used_; }
 
-  void set_next(MemEntryImpl* next) {
-    next_ = next;
-  }
+  // The in-memory size of this entry to use for the purposes of eviction.
+  int GetStorageSize() const;
 
-  void set_prev(MemEntryImpl* prev) {
-    prev_ = prev;
-  }
+  // Update an entry's position in the backend LRU list and set |last_used_|. If
+  // the entry was modified, also update |last_modified_|.
+  void UpdateStateOnUse(EntryModified modified_enum);
 
-  EntryType type() const {
-    return parent_ ? kChildEntry : kParentEntry;
-  }
-
-  const net::BoundNetLog& net_log() {
-    return net_log_;
-  }
-
-  // Entry interface.
+  // From disk_cache::Entry:
   void Doom() override;
   void Close() override;
   std::string GetKey() const override;
@@ -123,11 +127,15 @@ class MemEntryImpl : public Entry {
   int ReadyForSparseIO(const CompletionCallback& callback) override;
 
  private:
+  MemEntryImpl(MemBackendImpl* backend,
+               const std::string& key,
+               int child_id,
+               MemEntryImpl* parent,
+               net::NetLog* net_log);
+
   typedef base::hash_map<int, MemEntryImpl*> EntryMap;
 
-  enum {
-    NUM_STREAMS = 3
-  };
+  static const int kNumStreams = 3;
 
   ~MemEntryImpl() override;
 
@@ -138,53 +146,35 @@ class MemEntryImpl : public Entry {
                         bool truncate);
   int InternalReadSparseData(int64_t offset, IOBuffer* buf, int buf_len);
   int InternalWriteSparseData(int64_t offset, IOBuffer* buf, int buf_len);
-
-  // Old Entry interface.
-  int GetAvailableRange(int64_t offset, int len, int64_t* start);
-
-  // Grows and cleans up the data buffer.
-  void PrepareTarget(int index, int offset, int buf_len);
-
-  // Updates ranking information.
-  void UpdateRank(bool modified);
+  int InternalGetAvailableRange(int64_t offset, int len, int64_t* start);
 
   // Initializes the children map and sparse info. This method is only called
   // on a parent entry.
   bool InitSparseInfo();
 
-  // Performs the initialization of a MemEntryImpl as a child entry.
-  // |parent| is the pointer to the parent entry. |child_id| is the ID of
-  // the new child.
-  bool InitChildEntry(MemEntryImpl* parent, int child_id, net::NetLog* net_log);
-
   // Returns an entry responsible for |offset|. The returned entry can be a
   // child entry or this entry itself if |offset| points to the first range.
   // If such entry does not exist and |create| is true, a new child entry is
   // created.
-  MemEntryImpl* OpenChild(int64_t offset, bool create);
+  MemEntryImpl* GetChild(int64_t offset, bool create);
 
   // Finds the first child located within the range [|offset|, |offset + len|).
   // Returns the number of bytes ahead of |offset| to reach the first available
   // bytes in the entry. The first child found is output to |child|.
   int FindNextChild(int64_t offset, int len, MemEntryImpl** child);
 
-  // Removes child indexed by |child_id| from the children map.
-  void DetachChild(int child_id);
-
   std::string key_;
-  std::vector<char> data_[NUM_STREAMS];  // User data.
-  int32_t data_size_[NUM_STREAMS];
+  std::vector<char> data_[kNumStreams];  // User data.
   int ref_count_;
 
   int child_id_;              // The ID of a child entry.
   int child_first_pos_;       // The position of the first byte in a child
                               // entry.
-  MemEntryImpl* next_;        // Pointers for the LRU list.
-  MemEntryImpl* prev_;
-  MemEntryImpl* parent_;      // Pointer to the parent entry.
+  // Pointer to the parent entry, or nullptr if this entry is a parent entry.
+  MemEntryImpl* parent_;
   scoped_ptr<EntryMap> children_;
 
-  base::Time last_modified_;  // LRU information.
+  base::Time last_modified_;
   base::Time last_used_;
   MemBackendImpl* backend_;   // Back pointer to the cache.
   bool doomed_;               // True if this entry was removed from the cache.