base/task/sequence_manager: Reduce canceled task sweep allocation ove…

…rhead

To reduce the per-task allocation overhead, use a stack container for
holding swept cancelled tasks instead of always falling back to the
heap.

Bug: 1190643,1212886
Change-Id: I5871a25e52805316a9deea76d52c381175c49b1a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2917000
Commit-Queue: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Auto-Submit: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#886445}

base/task/sequence_manager/task_queue_impl.cc

@@ -9,6 +9,7 @@
 #include <memory>
 #include <utility>
 
+#include "base/containers/stack_container.h"
 #include "base/logging.h"
 #include "base/ranges/algorithm.h"
 #include "base/strings/stringprintf.h"
@@ -1391,15 +1392,16 @@ size_t TaskQueueImpl::DelayedIncomingQueue::PQueue::SweepCancelledTasks(
   // move all the cancelled tasks into a temporary container before deleting
   // them. This is to avoid |c| from changing while c.erase() is running.
   auto delete_start = std::stable_partition(c.begin(), c.end(), keep_task);
-  std::vector<Task> tasks_to_delete;
-  std::move(delete_start, c.end(), std::back_inserter(tasks_to_delete));
+  StackVector<Task, 8> tasks_to_delete;
+  std::move(delete_start, c.end(),
+            std::back_inserter(tasks_to_delete.container()));
   c.erase(delete_start, c.end());
 
   // stable_partition ensures order was not changed if there was nothing to
   // delete.
-  if (!tasks_to_delete.empty()) {
+  if (!tasks_to_delete->empty()) {
     ranges::make_heap(c, comp);
-    tasks_to_delete.clear();
+    tasks_to_delete->clear();
   }
   return num_high_res_tasks_swept;
 }

base/task/sequence_manager/work_queue.cc

@@ -4,6 +4,7 @@
 
 #include "base/task/sequence_manager/work_queue.h"
 
+#include "base/containers/stack_container.h"
 #include "base/debug/alias.h"
 #include "base/task/sequence_manager/sequence_manager_impl.h"
 #include "base/task/sequence_manager/work_queue_sets.h"
@@ -205,7 +206,7 @@ bool WorkQueue::RemoveAllCanceledTasksFromFront() {
   // Since task destructors could have a side-effect of deleting this task queue
   // we move cancelled tasks into a temporary container which can be emptied
   // without accessing |this|.
-  std::vector<Task> tasks_to_delete;
+  StackVector<Task, 8> tasks_to_delete;
 
   while (!tasks_.empty()) {
     const auto& pending_task = tasks_.front();
@@ -232,10 +233,10 @@ bool WorkQueue::RemoveAllCanceledTasksFromFront() {
 #endif  // !defined(OS_NACL)
     if (pending_task.task && !pending_task.task.IsCancelled())
       break;
-    tasks_to_delete.push_back(std::move(tasks_.front()));
+    tasks_to_delete->push_back(std::move(tasks_.front()));
     tasks_.pop_front();
   }
-  if (!tasks_to_delete.empty()) {
+  if (!tasks_to_delete->empty()) {
     if (tasks_.empty()) {
       // NB delayed tasks are inserted via Push, no don't need to reload those.
       if (queue_type_ == QueueType::kImmediate) {
@@ -253,7 +254,7 @@ bool WorkQueue::RemoveAllCanceledTasksFromFront() {
       work_queue_sets_->OnQueuesFrontTaskChanged(this);
     task_queue_->TraceQueueSize();
   }
-  return !tasks_to_delete.empty();
+  return !tasks_to_delete->empty();
 }
 
 void WorkQueue::AssignToWorkQueueSets(WorkQueueSets* work_queue_sets) {