SimpleCache: read small files all at once.

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 7ab6c38e4ef1bd55d1ba8a60a258dbfee94afca0..246ffd471e93c9794f9bb276e16761864179b1c6 100644
--- a/net/disk_cache/simple/simple_entry_impl.h
+++ b/net/disk_cache/simple/simple_entry_impl.h
@@ -312,8 +312,14 @@ 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);
+  // Completes a read from the stream data kept in memory, logging metrics
+  // and updating metadata as appropriate. If |callback| is non-null, it will
+  // be posted to with the return code.
+  void ReadInMemoryStreamData(net::GrowableIOBuffer* in_buf,

[pasko, 2017/08/04 01:28:34]

naming bikeshed: 'Stream' is slightly confusing because we are not providing
stream index to the method. Also seems important to reflect the posting
activity. Suggestion: ReadFromBufferAndPostReply()?

[Maks Orlovich, 2017/08/04 18:35:44]

Done.

+                              int offset,
+                              int buf_len,
+                              net::IOBuffer* out_buf,
+                              const CompletionCallback& callback);
 
   // Copies data from |buf| to the internal in-memory buffer for stream 0. If
   // |truncate| is set to true, the target buffer will be truncated at |offset|
@@ -341,6 +347,7 @@ class NET_EXPORT_PRIVATE SimpleEntryImpl : public Entry,
   const base::FilePath path_;
   const uint64_t entry_hash_;
   const bool use_optimistic_operations_;
+  bool is_initial_stream1_read_;  // used for metrics only.
   std::string key_;
 
   // |last_used_|, |last_modified_| and |data_size_| are copied from the
@@ -403,6 +410,12 @@ class NET_EXPORT_PRIVATE SimpleEntryImpl : public Entry,
   // used to write HTTP headers, the memory consumption of keeping it in memory
   // is acceptable.
   scoped_refptr<net::GrowableIOBuffer> stream_0_data_;
+
+  // Sometimes stream 1 data is prefetched when stream 0 is first read, to make
+  // the first read call on stream 1 synchronous. If a write to the stream

[pasko, 2017/08/04 01:28:34]

oops, it's not synchronous because we PostTask every time. Apologies if I
suggested this formulation, I forgot that we do not return synchronously.

[Maks Orlovich, 2017/08/04 18:35:43]

So did I, actually. I think this was the original motivation Josh had, but it
kinda got overtaken by me liking single-read. Dropped this sentence.

+  // occurs on the entry the prefetch buffer is discarded. It may also be
+  // null if it wasn't prefetched in the first place.
+  scoped_refptr<net::GrowableIOBuffer> stream_1_prefetch_data_;
 };
 
 }  // namespace disk_cache