[fsp] Improve performance for reading small chunks of data.

webkit/browser/fileapi/file_system_context.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_CONTEXT_H_
 #define WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_CONTEXT_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 228 matching lines @@
   // Creates new FileStreamReader instance to read a file pointed by the given
   // filesystem URL |url| starting from |offset|. |expected_modification_time|
   // specifies the expected last modification if the value is non-null, the
   // reader will check the underlying file's actual modification time to see if
   // the file has been modified, and if it does any succeeding read operations
   // should fail with ERR_UPLOAD_FILE_CHANGED error.
   // This method internally cracks the |url|, get an appropriate
   // FileSystemBackend for the URL and call the backend's CreateFileReader.
   // The resolved FileSystemBackend could perform further specialization
   // depending on the filesystem type pointed by the |url|.
+  // The |length| argument says how many bytes are going to be read using the
+  // instance of the file stream reader. If unknown, then equal to -1.

[hashimoto, 2014/08/22 06:53:42]

Why don't you use kuint64max (or kint64max) to be consistent with existing code?
This way, you don't have to handle -1 specially.

[mtomasz, 2014/08/25 03:32:31]

Seems that kuint64max and kint64max are deprecated. So instead of simple -1 we
would have the following code:

#include <limits>
(...)
CreateFileStreamReader(..., numeric_limits<uint64>::max(), ...)

This is just way longer than -1. Also IMHO less readable.

[hashimoto, 2014/09/01 11:01:01]

I'm asking about consistency with the existing code, not about the length or the
readability of the code.
Also, using -1 is less intuitive than numeric_limits<uint64>::max(). (at least
-1 should be a constant.)

   scoped_ptr<webkit_blob::FileStreamReader> CreateFileStreamReader(
       const FileSystemURL& url,
       int64 offset,
+      int64 length,
       const base::Time& expected_modification_time);
 
   // Creates new FileStreamWriter instance to write into a file pointed by
   // |url| from |offset|.
   scoped_ptr<FileStreamWriter> CreateFileStreamWriter(
       const FileSystemURL& url,
       int64 offset);
 
   // Creates a new FileSystemOperationRunner.
   scoped_ptr<FileSystemOperationRunner> CreateFileSystemOperationRunner();
@@ skipping 151 matching lines @@
 
 struct DefaultContextDeleter {
   static void Destruct(const FileSystemContext* context) {
     context->DeleteOnCorrectThread();
   }
 };
 
 }  // namespace fileapi
 
 #endif  // WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_CONTEXT_H_