SimpleCache: merge the first and second stream in one file

net/disk_cache/simple/simple_entry_impl.h

Index: net/disk_cache/simple/simple_entry_impl.h
diff --git a/net/disk_cache/simple/simple_entry_impl.h b/net/disk_cache/simple/simple_entry_impl.h
index d7d9b8f942a06ae6373b764b2358116e9353092b..d0f3c34aa3ca70a5af1160cbf5d7419090976896 100644
--- a/net/disk_cache/simple/simple_entry_impl.h
+++ b/net/disk_cache/simple/simple_entry_impl.h
@@ -25,6 +25,7 @@ class TaskRunner;
 }
 
 namespace net {
+class GrowableIOBuffer;
 class IOBuffer;
 }
 
@@ -217,7 +218,7 @@ class NET_EXPORT_PRIVATE SimpleEntryImpl : public Entry,
                              int offset,
                              const CompletionCallback& completion_callback,
                              scoped_ptr<uint32> read_crc32,
-                             scoped_ptr<base::Time> last_used,
+                             scoped_ptr<SimpleEntryStat> entry_stat,
                              scoped_ptr<int> result);
 
   // Called after an asynchronous write completes.
@@ -251,6 +252,14 @@ class NET_EXPORT_PRIVATE SimpleEntryImpl : public Entry,
   void RecordReadIsParallelizable(const SimpleEntryOperation& operation) const;
   void RecordWriteDependencyType(const SimpleEntryOperation& operation) const;
 
+  // Reads from the stream 0 data kept in memory.
+  int ReadStream0Data(net::IOBuffer* buf, int offset, int buf_len);
+
+  // Copies stream 0 data to the buffer kept in memory.
+  int CopyStream0Data(net::IOBuffer* buf,
+                      int offset, int buf_len,
+                      bool truncate);

[pasko, 2013/09/17 14:17:36]

since this function does not change the state of |buf|, it should be a const
reference. Also the comment is confusing, one might think that "the buffer kept
in memory" is |buf|. I would rephrase it like this: "Copies data from |buf| to
the internal in-memory buffer for stream 0."

nit: it would be useful to add a clarification that |truncate| if set to true
causes the target buffer to be truncated at |offset| before being written.

[clamy, 2013/09/18 16:17:14]

net::IOBuffer::data() is not const, and used in this function.

Done for the comment.

+
   // All nonstatic SimpleEntryImpl methods should always be called on the IO
   // thread, in all cases. |io_thread_checker_| documents and enforces this.
   base::ThreadChecker io_thread_checker_;
@@ -268,7 +277,7 @@ class NET_EXPORT_PRIVATE SimpleEntryImpl : public Entry,
   // TODO(clamy): Unify last_used_ with data in the index.
   base::Time last_used_;
   base::Time last_modified_;
-  int32 data_size_[kSimpleEntryFileCount];
+  int32 data_size_[kSimpleEntryStreamCount];
 
   // Number of times this object has been returned from Backend::OpenEntry() and
   // Backend::CreateEntry() without subsequent Entry::Close() calls. Used to
@@ -283,15 +292,15 @@ class NET_EXPORT_PRIVATE SimpleEntryImpl : public Entry,
   // write. For each stream, |crc32s_[index]| is the crc32 of that stream from
   // [0 .. |crc32s_end_offset_|). If |crc32s_end_offset_[index] == 0| then the
   // value of |crc32s_[index]| is undefined.
-  int32 crc32s_end_offset_[kSimpleEntryFileCount];
-  uint32 crc32s_[kSimpleEntryFileCount];
+  int32 crc32s_end_offset_[kSimpleEntryStreamCount];
+  uint32 crc32s_[kSimpleEntryStreamCount];
 
   // If |have_written_[index]| is true, we have written to the stream |index|.

[Deprecated (see juliatuttle), 2013/09/16 20:01:52]

This comment is no longer strictly true; we set have_written_[0] if we write to
stream 1, since we will need to rewrite stream 1 also.

[clamy, 2013/09/17 13:59:42]

Done.

-  bool have_written_[kSimpleEntryFileCount];
+  bool have_written_[kSimpleEntryStreamCount];
 
   // Reflects how much CRC checking has been done with the entry. This state is
   // reported on closing each entry stream.
-  CheckCrcResult crc_check_state_[kSimpleEntryFileCount];
+  CheckCrcResult crc_check_state_[kSimpleEntryStreamCount];
 
   // The |synchronous_entry_| is the worker thread object that performs IO on
   // entries. It's owned by this SimpleEntryImpl whenever |executing_operation_|
@@ -306,6 +315,16 @@ class NET_EXPORT_PRIVATE SimpleEntryImpl : public Entry,
   net::BoundNetLog net_log_;
 
   scoped_ptr<SimpleEntryOperation> executing_operation_;
+
+  // Unlike other streams, stream 0 data is read from the disk when the entry is
+  // opened, and then kept in memory. All read/write operations on stream 0
+  // affect the |stream_0_data_| buffer. When the entry is closed,
+  // |stream_0_data_| is written to the disk.
+  // Stream 0 is kept in memory because it is stored in the same file than

[pasko, 2013/09/17 14:17:36]

s/than/as/

s/(to save diskspace)// <-- since we also save on file the amount of open file
descriptors, which is arguably more important

[clamy, 2013/09/18 16:17:14]

Done.

+  // stream 1 on disk (to save diskspace). This strategy allows stream 1 to
+  // change size easily. Since stream 0 is only used to write HTTP headers, the
+  // memory consumption of keeping it in memory is acceptable.
+  scoped_refptr<net::GrowableIOBuffer> stream_0_data_;
 };
 
 }  // namespace disk_cache