Don't create parallel request if download is about to complete

content/browser/download/parallel_download_job.cc

Index: content/browser/download/parallel_download_job.cc
diff --git a/content/browser/download/parallel_download_job.cc b/content/browser/download/parallel_download_job.cc
index 0dc7cdda3a196687fac868df8e99c3642f4e67c3..5a3af37402aec99f0743fa73cbc5b583f4a12cb0 100644
--- a/content/browser/download/parallel_download_job.cc
+++ b/content/browser/download/parallel_download_job.cc
@@ -4,7 +4,11 @@
 
 #include "content/browser/download/parallel_download_job.h"
 
+#include <algorithm>
+
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/time/time.h"
 #include "content/browser/download/download_create_info.h"
 #include "content/browser/download/download_stats.h"
 #include "content/browser/download/parallel_download_utils.h"
@@ -80,10 +84,15 @@ void ParallelDownloadJob::Resume(bool resume_request) {
 int ParallelDownloadJob::GetParallelRequestCount() const {
   return GetParallelRequestCountConfig();
 }
+
 int64_t ParallelDownloadJob::GetMinSliceSize() const {
   return GetMinSliceSizeConfig();
 }
 
+int ParallelDownloadJob::GetMinRemainingTimeInSeconds() const {
+  return GetParallelRequestRemainingTimeConfig().InSeconds();
+}
+
 bool ParallelDownloadJob::UsesParallelRequests() const {
   return true;
 }
@@ -149,15 +158,30 @@ void ParallelDownloadJob::BuildParallelRequests() {
 
   // Create more slices for a new download. The initial request may generate
   // a received slice.
-  if (slices_to_download.size() <= 1 &&
-      initial_request_offset_ <= first_slice_offset) {
-    // 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 pieces to different workers.
-    // Otherwise, just fork |slices_to_download.size()| number of workers.
-    slices_to_download = FindSlicesForRemainingContent(
-        first_slice_offset,
-        content_length_ - first_slice_offset + initial_request_offset_,
-        GetParallelRequestCount(), GetMinSliceSize());
+  if (slices_to_download.size() <= 1 && download_item_->GetTotalBytes() > 0) {
+    int64_t current_bytes_per_second =
+        std::max(static_cast<int64_t>(1), download_item_->CurrentSpeed());
+    int64_t remaining_bytes =
+        download_item_->GetTotalBytes() - download_item_->GetReceivedBytes();
+
+    int64_t remaining_time = remaining_bytes / current_bytes_per_second;
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+        "Download.ParallelDownload.RemainingTimeWhenBuildingRequests",
+        remaining_time, 0, base::TimeDelta::FromDays(1).InSeconds(), 50);
+    if (remaining_bytes / current_bytes_per_second >
+        GetMinRemainingTimeInSeconds()) {
+      // 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 pieces to different
+      // workers. Otherwise, just fork |slices_to_download.size()| number of
+      // workers.
+      slices_to_download = FindSlicesForRemainingContent(
+          first_slice_offset,
+          content_length_ - first_slice_offset + initial_request_offset_,
+          GetParallelRequestCount(), GetMinSliceSize());
+    } else {
+      RecordParallelDownloadCreationEvent(
+          ParallelDownloadCreationEvent::FALLBACK_REASON_REMAINING_TIME);
+    }
   }
 
   DCHECK(!slices_to_download.empty());