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

webkit/browser/blob/blob_url_request_job.cc

 // 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.
 
 #include "webkit/browser/blob/blob_url_request_job.h"
 
+#include <algorithm>
 #include <limits>
+#include <string>
+#include <vector>

[hashimoto, 2014/09/05 03:17:27]

nit: Are these include needed?

[mtomasz, 2014/09/05 05:31:42]

algorithm for std::min.
string for std::string.
vector for std::vector.

All used in this file.

 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_util_proxy.h"
 #include "base/format_macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/message_loop/message_loop_proxy.h"
+#include "base/numerics/safe_conversions.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_response_headers.h"
 #include "net/http/http_response_info.h"
 #include "net/http/http_util.h"
 #include "net/url_request/url_request.h"
@@ skipping 190 matching lines @@
     NotifyFailure(error);
     return;
   }
 
   // Apply the range requirement.
   if (!byte_range_.ComputeBounds(total_size_)) {
     NotifyFailure(net::ERR_REQUEST_RANGE_NOT_SATISFIABLE);
     return;
   }
 
-  remaining_bytes_ = byte_range_.last_byte_position() -
-                     byte_range_.first_byte_position() + 1;
+  remaining_bytes_ = base::checked_cast<int64>(
+      byte_range_.last_byte_position() - byte_range_.first_byte_position() + 1);
   DCHECK_GE(remaining_bytes_, 0);
 
   // Do the seek at the beginning of the request.
   if (byte_range_.first_byte_position())
     Seek(byte_range_.first_byte_position());
 
   NotifySuccess();
 }
 
 void BlobURLRequestJob::DidGetFileItemLength(size_t index, int64 result) {
@@ skipping 332 matching lines @@
           item.path(),
           item.offset() + additional_offset,
           item.expected_modification_time());
       break;
     case BlobData::Item::TYPE_FILE_FILESYSTEM:
       reader = file_system_context_->CreateFileStreamReader(
                                          storage::FileSystemURL(
                                              file_system_context_->CrackURL(
                                                  item.filesystem_url())),
                                          item.offset() + additional_offset,
+                                         item.length() - additional_offset,

[hashimoto, 2014/09/05 03:17:27]

Shouldn't item_length_list_ be used here?

[mtomasz, 2014/09/05 05:31:42]

While filling out item_length_list_, file stream readers are lazily created, so
basically item_length_list_[index] may be undefined at this stage.

However, item.length() may be -1 (aka max int64) here, so I added an extra
check. BTW. In this file static_cast<uint64>(-1) is used, which I find weird and
tricky, so replaced with numeric_limits.

                                          item.expected_modification_time())
                    .release();
       break;
     default:
       NOTREACHED();
   }
   DCHECK(reader);
   index_to_reader_[index] = reader;
 }
 
 }  // namespace storage