Add a delay to send the parallel requests.

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 {
 
 ParallelDownloadJob::ParallelDownloadJob(
     DownloadItemImpl* download_item,
     std::unique_ptr<DownloadRequestHandleInterface> request_handle,
     const DownloadCreateInfo& create_info)
     : DownloadJobImpl(download_item, std::move(request_handle)),
       initial_request_offset_(create_info.save_info->offset),
-      initial_request_length_(create_info.save_info->length) {}
+      initial_request_length_(create_info.save_info->length),
+      requests_sent_(false) {}
 
 ParallelDownloadJob::~ParallelDownloadJob() = default;
 
 void ParallelDownloadJob::Start() {
   DownloadJobImpl::Start();
 
-  BuildParallelRequests();
+  BuildParallelRequestAfterDelay();
 }
 
 void ParallelDownloadJob::Cancel(bool user_cancel) {
   DownloadJobImpl::Cancel(user_cancel);
+
+  if (!requests_sent_) {
+    timer_.Stop();
+    return;
+  }
+
   for (auto& worker : workers_)
     worker->Cancel();
 }
 
 void ParallelDownloadJob::Pause() {
   DownloadJobImpl::Pause();
+
+  if (!requests_sent_) {
+    timer_.Stop();
+    return;
+  }
+
   for (auto& worker : workers_)
     worker->Pause();
 }
 
 void ParallelDownloadJob::Resume(bool resume_request) {
   DownloadJobImpl::Resume(resume_request);
   if (!resume_request)
     return;
 
+  // Send parallel requests if the download is paused previously.
+  if (!requests_sent_) {
+    if (!timer_.IsRunning())
+      BuildParallelRequestAfterDelay();
+    return;
+  }
+
   for (auto& worker : workers_)
     worker->Resume();
 }
 
 void ParallelDownloadJob::ForkRequestsForNewDownload(int64_t bytes_received,
                                                      int64_t total_bytes,
                                                      int request_count) {
   if (!download_item_ || total_bytes <= 0 || bytes_received >= total_bytes ||
       request_count <= 1) {
     return;
   }
 
   int64_t bytes_left = total_bytes - bytes_received;
   int64_t slice_size = bytes_left / request_count;
   slice_size = slice_size > 0 ? slice_size : 1;
   int num_requests = bytes_left / slice_size;
   int64_t current_offset = bytes_received + slice_size;
 
   // 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::BuildParallelRequestAfterDelay() {
+  DCHECK(workers_.empty());
+  DCHECK(!requests_sent_);
+  DCHECK(!timer_.IsRunning());
+
+  timer_.Start(FROM_HERE, GetParallelRequestDelayConfig(), this,
+               &ParallelDownloadJob::BuildParallelRequests);
+}
+
 void ParallelDownloadJob::BuildParallelRequests() {
+  if (requests_sent_)

[qinmin, 2017/03/16 17:40:36]

nit: DCHECK_FALSE(request_sent);

[xingliu, 2017/03/16 18:18:35]

Done.

+    return;
+
   // 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() >=
       static_cast<size_t>(GetParallelRequestCountConfig())) {
     // 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.
     // Otherwise, just fork |slices_to_download.size()| number of workers.
   }
+
+  requests_sent_ = true;
 }
 
 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());
 
@@ skipping 12 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