Disk cache: Introduce a BlockHeader class.

net/disk_cache/block_files.h

Index: net/disk_cache/block_files.h
===================================================================
--- net/disk_cache/block_files.h	(revision 205976)
+++ net/disk_cache/block_files.h	(working copy)
@@ -22,6 +22,53 @@
 
 namespace disk_cache {
 
+// An instance of this class represents the header of a block file in memory.
+// Note that this class doesn't perform any file operation.
+class BlockHeader {

[gavinp, 2013/06/14 15:37:02]

Is this class ever referenced in any translation unit other than block_files.cc?

I've gone through
https://codereview.chromium.org/download/issue15203004_15001.diff and I couldn't
find it.

[rvargas (doing something else), 2013/06/14 18:32:07]

Sure,
https://codereview.chromium.org/15203004/diff/15001/net/disk_cache/v3/backend...
line 334.

In other words, BackendImplV3 only uses BlockHeaders, not BlockFiles

[rvargas (doing something else), 2013/06/18 18:12:23]

I'm sorry, this was not completely accurate... there is a layer in between
BlockHeader and the backend: BlockBitmaps (v3/block_bitmaps.xx)... but the idea
is the same, the backend uses the same interface of BlockFiles, so there is a
class (BlockHeader) that implements that interface for an in-memory entity
(without doing IO)

+ public:
+  BlockHeader();
+  explicit BlockHeader(BlockFileHeader* header);
+  explicit BlockHeader(MappedFile* file);
+  BlockHeader(const BlockHeader& other);
+  ~BlockHeader();
+
+  // Creates a new entry on the allocation map, updating the apropriate
+  // counters. |target| is the type of block to use (number of empty blocks),
+  // and |size| is the actual number of blocks to use.
+  bool CreateMapBlock(int target, int size, int* index);
+
+  // Deletes the block pointed by |index|.
+  void DeleteMapBlock(int index, int block_size);
+
+  // Returns true if the specified block is used.
+  bool UsedMapBlock(int index, int size);
+
+  // Restores the "empty counters" and allocation hints.
+  void FixAllocationCounters();
+
+  // Returns true if the current block file should not be used as-is to store
+  // more records. |block_count| is the number of blocks to allocate.
+  bool NeedToGrowBlockFile(int block_count);
+
+  // Returns the number of empty blocks for this file.
+  int EmptyBlocks() const;
+
+  // Returns true if the counters look OK.
+  bool ValidateCounters() const;
+
+  // Returns the size of the wrapped structure (BlockFileHeader).
+  int Size() const;
+
+  BlockFileHeader* operator->() { return header_; }
+  void operator=(const BlockHeader& other) { header_ = other.header_; }
+  BlockFileHeader* Get() { return header_; }
+
+ private:
+  BlockFileHeader* header_;

[gavinp, 2013/06/14 15:37:02]

#include "net/disk_cache/disk_format_base.h"

[rvargas (doing something else), 2013/06/14 18:32:07]

Done.

+};
+
+typedef std::vector<BlockHeader> BlockFilesBitmaps;
+
 // This class handles the set of block-files open by the disk cache.
 class NET_EXPORT_PRIVATE BlockFiles {
  public: