Change FindNextSliceToDownload() into FindSlicesToDownload()

content/browser/download/parallel_download_job.cc

 // Copyright 2017 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/parallel_download_job.h"
 
 #include "base/memory/ptr_util.h"
+#include "content/browser/download/download_create_info.h"
+#include "content/browser/download/parallel_download_utils.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/storage_partition.h"
 
 namespace content {
 
 namespace {
 
 // TODO(xingliu): Use finch parameters to configure constants.
 // Default number of requests in a parallel download, including the original
 // request.
 const int kParallelRequestCount = 2;
 
 }  // namespace
 
 ParallelDownloadJob::ParallelDownloadJob(
     DownloadItemImpl* download_item,
-    std::unique_ptr<DownloadRequestHandleInterface> request_handle)
+    std::unique_ptr<DownloadRequestHandleInterface> request_handle,
+    const DownloadCreateInfo& create_info)
     : DownloadJobImpl(download_item, std::move(request_handle)),
-      request_num_(kParallelRequestCount) {}
+      request_num_(kParallelRequestCount),
+      initial_request_offset_(create_info.save_info->offset),
+      initial_request_length_(create_info.save_info->length) {}
 
 ParallelDownloadJob::~ParallelDownloadJob() = default;
 
+void ParallelDownloadJob::Start() {
+  DownloadJobImpl::Start();
+
+  BuildParallelRequests();
+}
+
 void ParallelDownloadJob::Cancel(bool user_cancel) {
   DownloadJobImpl::Cancel(user_cancel);
   for (auto& worker : workers_)
     worker->Cancel();
 }
 
 void ParallelDownloadJob::Pause() {
   DownloadJobImpl::Pause();
   for (auto& worker : workers_)
     worker->Pause();
@@ skipping 24 matching lines @@
   // TODO(xingliu): Add records for slices in history db.
   for (int i = 0; i < num_requests - 1; ++i) {
     int64_t length = (i == (num_requests - 2))
                          ? slice_size + (bytes_left % slice_size)
                          : slice_size;
     CreateRequest(current_offset, length);
     current_offset += slice_size;
   }
 }
 
+void ParallelDownloadJob::BuildParallelRequests() {
+  // Calculate the slices to download and fork parallel requests.
+  std::vector<DownloadItem::ReceivedSlice> slices_to_download =
+      FindSlicesToDownload(download_item_->GetReceivedSlices());
+  // The initial request has already been sent, it should cover the first slice.
+  DCHECK_GE(slices_to_download[0].offset, initial_request_offset_);
+  DCHECK(initial_request_length_ == DownloadSaveInfo::kLengthFullContent ||
+         initial_request_offset_ + initial_request_length_ >=
+             slices_to_download[0].offset +
+             slices_to_download[0].received_bytes);
+  if (slices_to_download.size() >= kParallelRequestCount) {
+    // The size of |slices_to_download| should be no larger than
+    // |kParallelRequestCount| unless |kParallelRequestCount| is changed after
+    // a download is interrupted. This could happen if we use finch to config
+    // the number of parallel requests.
+    // TODO(qinmin): Get the next |kParallelRequestCount - 1| slices and fork
+    // new requests. For the remaining slices, they will be handled once some
+    // of the workers finish their job.
+  } else {
+    // TODO(qinmin): Check the size of the last slice. If it is huge, we can
+    // split it into N pieces and pass the last N-1 pirces to different workers.

[xingliu, 2017/03/03 21:37:44]

nit, N-1 pieces.

[qinmin, 2017/03/03 22:09:43]

Done.

+    // Otherwise, just fork |slices_to_download.size()| number of workers.
+  }
+}
+
 void ParallelDownloadJob::CreateRequest(int64_t offset, int64_t length) {
   std::unique_ptr<DownloadWorker> worker = base::MakeUnique<DownloadWorker>();
 
   DCHECK(download_item_);
   StoragePartition* storage_partition =
       BrowserContext::GetStoragePartitionForSite(
           download_item_->GetBrowserContext(), download_item_->GetSiteUrl());
 
   std::unique_ptr<DownloadUrlParameters> download_params(
       new DownloadUrlParameters(download_item_->GetURL(),
@@ skipping 10 matching lines @@
   // Subsequent range requests have the same referrer URL as the original
   // download request.
   download_params->set_referrer(Referrer(download_item_->GetReferrerUrl(),
                                          blink::WebReferrerPolicyAlways));
   // Send the request.
   worker->SendRequest(std::move(download_params));
   workers_.push_back(std::move(worker));
 }
 
 }  // namespace content