Glue parallel download job and download file together.

content/browser/download/download_file_impl.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 "content/browser/download/download_file_impl.h"
 
 #include <string>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 102 matching lines @@
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE, base::Bind(callback, result));
     return;
   }
 
   download_start_ = base::TimeTicks::Now();
 
   // Primarily to make reset to zero in restart visible to owner.
   SendUpdate();
 
-  // Initial pull from the straw.
+  // Initial pull from the straw from all source streams.
   for (auto& source_stream : source_streams_)
     RegisterAndActivateStream(source_stream.second.get());
 
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE, base::Bind(
           callback, DOWNLOAD_INTERRUPT_REASON_NONE));
 }
 
 void DownloadFileImpl::AddByteStream(
     std::unique_ptr<ByteStreamReader> stream_reader,
-    int64_t offset) {
+    int64_t offset,
+    int64_t length) {
   DCHECK_CURRENTLY_ON(BrowserThread::FILE);
+  DCHECK(source_streams_.find(offset) == source_streams_.end());
 
-  // The |source_streams_| must have an existing entry for the stream reader.
-  auto current_source_stream = source_streams_.find(offset);
-  DCHECK(current_source_stream != source_streams_.end());
-  SourceStream* stream = current_source_stream->second.get();
+  source_streams_[offset] = base::MakeUnique<SourceStream>(offset, length);
+  SourceStream* stream = source_streams_[offset].get();
   stream->SetByteStream(std::move(stream_reader));

[asanka, 2017/03/14 19:44:01]

Are all SourceStream constructions immediately followed by SetByteStream? If so
we could move the byte stream into the constructor and get rid of SetByteStream.

[xingliu, 2017/03/14 22:48:29]

Done,

Thanks for this suggestion, yeah, this makes sense now.

 
-  RegisterAndActivateStream(stream);
+  // If the file is initialized, start to write data, or wait until file opened.
+  if (file_.in_progress())
+    RegisterAndActivateStream(stream);
 }
 
 DownloadInterruptReason DownloadFileImpl::WriteDataToFile(int64_t offset,
                                                           const char* data,
                                                           size_t data_len) {
   DCHECK_CURRENTLY_ON(BrowserThread::FILE);
   WillWriteToDisk(data_len);
   return file_.WriteDataToFile(offset, data, data_len);
 }
 
@@ skipping 291 matching lines @@
     const base::FilePath& new_path,
     const RenameCompletionCallback& completion_callback)
     : option(option),
       new_path(new_path),
       retries_left(kMaxRenameRetries),
       completion_callback(completion_callback) {}
 
 DownloadFileImpl::RenameParameters::~RenameParameters() {}
 
 }  // namespace content