Move blink scheduler implementation into a component

content/child/scheduler/prioritizing_task_queue_selector.cc

-// Copyright 2014 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/child/scheduler/prioritizing_task_queue_selector.h"
-
-#include "base/logging.h"
-#include "base/pending_task.h"
-#include "base/trace_event/trace_event_argument.h"
-
-namespace content {
-
-PrioritizingTaskQueueSelector::PrioritizingTaskQueueSelector()
-    : starvation_count_(0), task_queue_selector_observer_(nullptr) {
-}
-
-PrioritizingTaskQueueSelector::~PrioritizingTaskQueueSelector() {
-}
-
-void PrioritizingTaskQueueSelector::RegisterWorkQueues(
-    const std::vector<const base::TaskQueue*>& work_queues) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  work_queues_ = work_queues;
-  for (auto& queue_priority : queue_priorities_) {
-    queue_priority.clear();
-  }
-
-  // By default, all work queues are set to normal priority.
-  for (size_t i = 0; i < work_queues.size(); i++) {
-    queue_priorities_[NORMAL_PRIORITY].insert(i);
-  }
-}
-
-void PrioritizingTaskQueueSelector::SetQueuePriority(size_t queue_index,
-                                                     QueuePriority priority) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  DCHECK_LT(queue_index, work_queues_.size());
-  DCHECK_LT(priority, QUEUE_PRIORITY_COUNT);
-  bool previously_enabled = DisableQueueInternal(queue_index);
-  queue_priorities_[priority].insert(queue_index);
-  if (task_queue_selector_observer_ && !previously_enabled)
-    task_queue_selector_observer_->OnTaskQueueEnabled();
-}
-
-void PrioritizingTaskQueueSelector::EnableQueue(size_t queue_index,
-                                                QueuePriority priority) {
-  SetQueuePriority(queue_index, priority);
-}
-
-void PrioritizingTaskQueueSelector::DisableQueue(size_t queue_index) {
-  DisableQueueInternal(queue_index);
-}
-
-bool PrioritizingTaskQueueSelector::DisableQueueInternal(size_t queue_index) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  DCHECK_LT(queue_index, work_queues_.size());
-  bool previously_enabled = false;
-  for (auto& queue_priority : queue_priorities_) {
-    if (queue_priority.erase(queue_index))
-      previously_enabled = true;
-  }
-  return previously_enabled;
-}
-
-bool PrioritizingTaskQueueSelector::IsQueueEnabled(size_t queue_index) const {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  DCHECK_LT(queue_index, work_queues_.size());
-  for (const auto& queue_priority : queue_priorities_) {
-    if (queue_priority.find(queue_index) != queue_priority.end())
-      return true;
-  }
-  return false;
-}
-
-bool PrioritizingTaskQueueSelector::IsOlder(const base::TaskQueue* queueA,
-                                            const base::TaskQueue* queueB) {
-  // Note: the comparison is correct due to the fact that the PendingTask
-  // operator inverts its comparison operation in order to work well in a heap
-  // based priority queue.
-  return queueB->front() < queueA->front();
-}
-
-PrioritizingTaskQueueSelector::QueuePriority
-PrioritizingTaskQueueSelector::NextPriority(QueuePriority priority) {
-  DCHECK(priority < QUEUE_PRIORITY_COUNT);
-  return static_cast<QueuePriority>(static_cast<int>(priority) + 1);
-}
-
-bool PrioritizingTaskQueueSelector::ChooseOldestWithPriority(
-    QueuePriority priority,
-    size_t* out_queue_index) const {
-  bool found_non_empty_queue = false;
-  size_t chosen_queue = 0;
-  for (int queue_index : queue_priorities_[priority]) {
-    if (work_queues_[queue_index]->empty()) {
-      continue;
-    }
-    if (!found_non_empty_queue ||
-        IsOlder(work_queues_[queue_index], work_queues_[chosen_queue])) {
-      found_non_empty_queue = true;
-      chosen_queue = queue_index;
-    }
-  }
-
-  if (found_non_empty_queue) {
-    *out_queue_index = chosen_queue;
-  }
-  return found_non_empty_queue;
-}
-
-bool PrioritizingTaskQueueSelector::SelectWorkQueueToService(
-    size_t* out_queue_index) {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  DCHECK(work_queues_.size());
-  // Always service the control queue if it has any work.
-  if (ChooseOldestWithPriority(CONTROL_PRIORITY, out_queue_index)) {
-    DidSelectQueueWithPriority(CONTROL_PRIORITY);
-    return true;
-  }
-  // Select from the normal priority queue if we are starving it.
-  if (starvation_count_ >= kMaxStarvationTasks &&
-      ChooseOldestWithPriority(NORMAL_PRIORITY, out_queue_index)) {
-    DidSelectQueueWithPriority(NORMAL_PRIORITY);
-    return true;
-  }
-  // Otherwise choose in priority order.
-  for (QueuePriority priority = HIGH_PRIORITY; priority < QUEUE_PRIORITY_COUNT;
-       priority = NextPriority(priority)) {
-    if (ChooseOldestWithPriority(priority, out_queue_index)) {
-      DidSelectQueueWithPriority(priority);
-      return true;
-    }
-  }
-  return false;
-}
-
-void PrioritizingTaskQueueSelector::DidSelectQueueWithPriority(
-    QueuePriority priority) {
-  switch (priority) {
-    case CONTROL_PRIORITY:
-      break;
-    case HIGH_PRIORITY:
-      starvation_count_++;
-      break;
-    case NORMAL_PRIORITY:
-    case BEST_EFFORT_PRIORITY:
-      starvation_count_ = 0;
-      break;
-    default:
-      NOTREACHED();
-  }
-}
-
-// static
-const char* PrioritizingTaskQueueSelector::PriorityToString(
-    QueuePriority priority) {
-  switch (priority) {
-    case CONTROL_PRIORITY:
-      return "control";
-    case HIGH_PRIORITY:
-      return "high";
-    case NORMAL_PRIORITY:
-      return "normal";
-    case BEST_EFFORT_PRIORITY:
-      return "best_effort";
-    default:
-      NOTREACHED();
-      return nullptr;
-  }
-}
-
-void PrioritizingTaskQueueSelector::AsValueInto(
-    base::trace_event::TracedValue* state) const {
-  DCHECK(main_thread_checker_.CalledOnValidThread());
-  state->BeginDictionary("priorities");
-  for (QueuePriority priority = FIRST_QUEUE_PRIORITY;
-       priority < QUEUE_PRIORITY_COUNT; priority = NextPriority(priority)) {
-    state->BeginArray(PriorityToString(priority));
-    for (size_t queue_index : queue_priorities_[priority])
-      state->AppendInteger(queue_index);
-    state->EndArray();
-  }
-  state->EndDictionary();
-  state->SetInteger("starvation_count", starvation_count_);
-}
-
-void PrioritizingTaskQueueSelector::SetTaskQueueSelectorObserver(
-    Observer* observer) {
-  task_queue_selector_observer_ = observer;
-}
-
-}  // namespace content