content/child/scheduler/task_queue_manager.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/child/scheduler/task_queue_manager.h"
   6
   7 #include <queue>
   8 #include <set>
   9
  10 #include "base/bind.h"
  11 #include "base/trace_event/trace_event.h"
  12 #include "base/trace_event/trace_event_argument.h"
  13 #include "cc/test/test_now_source.h"
  14 #include "content/child/scheduler/nestable_single_thread_task_runner.h"
  15 #include "content/child/scheduler/task_queue_selector.h"
  16
  17 namespace {
  18 const int64_t kMaxTimeTicks = std::numeric_limits<int64>::max();
  19 }
  20
  21 namespace content {
  22 namespace internal {
  23
  24 // Now() is somewhat expensive so it makes sense not to call Now() unless we
  25 // really need to.
  26 class LazyNow {
  27  public:
  28   explicit LazyNow(base::TimeTicks now)
  29       : task_queue_manager_(nullptr), now_(now) {
  30     DCHECK(!now.is_null());
  31   }
  32
  33   explicit LazyNow(TaskQueueManager* task_queue_manager)
  34       : task_queue_manager_(task_queue_manager) {}
  35
  36   base::TimeTicks Now() {
  37     if (now_.is_null())
  38       now_ = task_queue_manager_->Now();
  39     return now_;
  40   }
  41
  42  private:
  43   TaskQueueManager* task_queue_manager_;  // NOT OWNED
  44   base::TimeTicks now_;
  45 };
  46
  47 class TaskQueue : public base::SingleThreadTaskRunner {
  48  public:
  49   TaskQueue(TaskQueueManager* task_queue_manager,
  50             const char* disabled_by_default_tracing_category);
  51
  52   // base::SingleThreadTaskRunner implementation.
  53   bool RunsTasksOnCurrentThread() const override;
  54   bool PostDelayedTask(const tracked_objects::Location& from_here,
  55                        const base::Closure& task,
  56                        base::TimeDelta delay) override {
  57     return PostDelayedTaskImpl(from_here, task, delay, TaskType::NORMAL);
  58   }
  59
  60   bool PostNonNestableDelayedTask(const tracked_objects::Location& from_here,
  61                                   const base::Closure& task,
  62                                   base::TimeDelta delay) override {
  63     return PostDelayedTaskImpl(from_here, task, delay, TaskType::NON_NESTABLE);
  64   }
  65
  66   bool IsQueueEmpty() const;
  67
  68   void SetPumpPolicy(TaskQueueManager::PumpPolicy pump_policy);
  69   void PumpQueue();
  70
  71   bool NextPendingDelayedTaskRunTime(
  72       base::TimeTicks* next_pending_delayed_task);
  73
  74   bool UpdateWorkQueue(LazyNow* lazy_now,
  75                        const base::PendingTask* previous_task);
  76   base::PendingTask TakeTaskFromWorkQueue();
  77
  78   void WillDeleteTaskQueueManager();
  79
  80   base::TaskQueue& work_queue() { return work_queue_; }
  81
  82   void set_name(const char* name) { name_ = name; }
  83
  84   void AsValueInto(base::trace_event::TracedValue* state) const;
  85
  86  private:
  87   enum class TaskType {
  88     NORMAL,
  89     NON_NESTABLE,
  90   };
  91
  92   ~TaskQueue() override;
  93
  94   bool PostDelayedTaskImpl(const tracked_objects::Location& from_here,
  95                            const base::Closure& task,
  96                            base::TimeDelta delay,
  97                            TaskType task_type);
  98
  99   // Delayed task posted to the underlying run loop, which locks |lock_| and
 100   // calls MoveReadyDelayedTasksToIncomingQueueLocked to process dealyed tasks
 101   // that need to be run now.
 102   void MoveReadyDelayedTasksToIncomingQueue();
 103
 104   // Enqueues any delayed tasks which should be run now on the incoming_queue_
 105   // and calls ScheduleDelayedWorkLocked to ensure future tasks are scheduled.
 106   // Must be called with |lock_| locked.
 107   void MoveReadyDelayedTasksToIncomingQueueLocked(LazyNow* lazy_now);
 108
 109   // Posts MoveReadyDelayedTasksToIncomingQueue if there isn't already a task
 110   // posted on the underlying runloop for the next task's scheduled run time.
 111   void ScheduleDelayedWorkLocked(LazyNow* lazy_now);
 112
 113   void PumpQueueLocked();
 114   bool TaskIsOlderThanQueuedTasks(const base::PendingTask* task);
 115   bool ShouldAutoPumpQueueLocked(const base::PendingTask* previous_task);
 116   void EnqueueTaskLocked(const base::PendingTask& pending_task);
 117
 118   void TraceQueueSize(bool is_locked) const;
 119   static const char* PumpPolicyToString(
 120       TaskQueueManager::PumpPolicy pump_policy);
 121   static void QueueAsValueInto(const base::TaskQueue& queue,
 122                                base::trace_event::TracedValue* state);
 123   static void QueueAsValueInto(const base::DelayedTaskQueue& queue,
 124                                base::trace_event::TracedValue* state);
 125   static void TaskAsValueInto(const base::PendingTask& task,
 126                               base::trace_event::TracedValue* state);
 127
 128   // This lock protects all members except the work queue and the
 129   // main_thread_checker_.
 130   mutable base::Lock lock_;
 131   base::PlatformThreadId thread_id_;
 132   TaskQueueManager* task_queue_manager_;
 133   base::TaskQueue incoming_queue_;
 134   TaskQueueManager::PumpPolicy pump_policy_;
 135   const char* name_;
 136   const char* disabled_by_default_tracing_category_;
 137   base::DelayedTaskQueue delayed_task_queue_;
 138   std::set<base::TimeTicks> in_flight_kick_delayed_tasks_;
 139
 140   base::ThreadChecker main_thread_checker_;
 141   base::TaskQueue work_queue_;
 142
 143   DISALLOW_COPY_AND_ASSIGN(TaskQueue);
 144 };
 145
 146 TaskQueue::TaskQueue(TaskQueueManager* task_queue_manager,
 147                      const char* disabled_by_default_tracing_category)
 148     : thread_id_(base::PlatformThread::CurrentId()),
 149       task_queue_manager_(task_queue_manager),
 150       pump_policy_(TaskQueueManager::PumpPolicy::AUTO),
 151       name_(nullptr),
 152       disabled_by_default_tracing_category_(
 153           disabled_by_default_tracing_category) {
 154 }
 155
 156 TaskQueue::~TaskQueue() {
 157 }
 158
 159 void TaskQueue::WillDeleteTaskQueueManager() {
 160   base::AutoLock lock(lock_);
 161   task_queue_manager_ = nullptr;
 162   delayed_task_queue_ = base::DelayedTaskQueue();
 163   incoming_queue_ = base::TaskQueue();
 164   work_queue_ = base::TaskQueue();
 165 }
 166
 167 bool TaskQueue::RunsTasksOnCurrentThread() const {
 168   base::AutoLock lock(lock_);
 169   return base::PlatformThread::CurrentId() == thread_id_;
 170 }
 171
 172 bool TaskQueue::PostDelayedTaskImpl(const tracked_objects::Location& from_here,
 173                                     const base::Closure& task,
 174                                     base::TimeDelta delay,
 175                                     TaskType task_type) {
 176   base::AutoLock lock(lock_);
 177   if (!task_queue_manager_)
 178     return false;
 179
 180   base::PendingTask pending_task(from_here, task, base::TimeTicks(),
 181                                  task_type != TaskType::NON_NESTABLE);
 182   task_queue_manager_->DidQueueTask(&pending_task);
 183
 184   if (delay > base::TimeDelta()) {
 185     base::TimeTicks now = task_queue_manager_->Now();
 186     pending_task.delayed_run_time = now + delay;
 187     delayed_task_queue_.push(pending_task);
 188     TraceQueueSize(true);
 189     // If we changed the topmost task, then it is time to reschedule.
 190     if (delayed_task_queue_.top().task.Equals(pending_task.task)) {
 191       LazyNow lazy_now(now);
 192       ScheduleDelayedWorkLocked(&lazy_now);
 193     }
 194     return true;
 195   }
 196   EnqueueTaskLocked(pending_task);
 197   return true;
 198 }
 199
 200 void TaskQueue::MoveReadyDelayedTasksToIncomingQueue() {
 201   DCHECK(main_thread_checker_.CalledOnValidThread());
 202   base::AutoLock lock(lock_);
 203   if (!task_queue_manager_)
 204     return;
 205
 206   LazyNow lazy_now(task_queue_manager_);
 207   MoveReadyDelayedTasksToIncomingQueueLocked(&lazy_now);
 208 }
 209
 210 void TaskQueue::MoveReadyDelayedTasksToIncomingQueueLocked(LazyNow* lazy_now) {
 211   lock_.AssertAcquired();
 212   // Enqueue all delayed tasks that should be running now.
 213   while (!delayed_task_queue_.empty() &&
 214          delayed_task_queue_.top().delayed_run_time <= lazy_now->Now()) {
 215     in_flight_kick_delayed_tasks_.erase(
 216         delayed_task_queue_.top().delayed_run_time);
 217     EnqueueTaskLocked(delayed_task_queue_.top());
 218     delayed_task_queue_.pop();
 219   }
 220   TraceQueueSize(true);
 221   ScheduleDelayedWorkLocked(lazy_now);
 222 }
 223
 224 void TaskQueue::ScheduleDelayedWorkLocked(LazyNow* lazy_now) {
 225   lock_.AssertAcquired();
 226   // Any remaining tasks are in the future, so queue a task to kick them.
 227   if (!delayed_task_queue_.empty()) {
 228     base::TimeTicks next_run_time = delayed_task_queue_.top().delayed_run_time;
 229     DCHECK_GT(next_run_time, lazy_now->Now());
 230     // Make sure we don't have more than one
 231     // MoveReadyDelayedTasksToIncomingQueue posted for a particular scheduled
 232     // run time (note it's fine to have multiple ones in flight for distinct
 233     // run times).
 234     if (in_flight_kick_delayed_tasks_.find(next_run_time) ==
 235         in_flight_kick_delayed_tasks_.end()) {
 236       in_flight_kick_delayed_tasks_.insert(next_run_time);
 237       base::TimeDelta delay = next_run_time - lazy_now->Now();
 238       task_queue_manager_->PostDelayedTask(
 239           FROM_HERE,
 240           Bind(&TaskQueue::MoveReadyDelayedTasksToIncomingQueue, this), delay);
 241     }
 242   }
 243 }
 244
 245 bool TaskQueue::IsQueueEmpty() const {
 246   if (!work_queue_.empty())
 247     return false;
 248
 249   {
 250     base::AutoLock lock(lock_);
 251     return incoming_queue_.empty();
 252   }
 253 }
 254
 255 bool TaskQueue::TaskIsOlderThanQueuedTasks(const base::PendingTask* task) {
 256   lock_.AssertAcquired();
 257   // A null task is passed when UpdateQueue is called before any task is run.
 258   // In this case we don't want to pump an after_wakeup queue, so return true
 259   // here.
 260   if (!task)
 261     return true;
 262
 263   // Return false if there are no task in the incoming queue.
 264   if (incoming_queue_.empty())
 265     return false;
 266
 267   base::PendingTask oldest_queued_task = incoming_queue_.front();
 268   DCHECK(oldest_queued_task.delayed_run_time.is_null());
 269   DCHECK(task->delayed_run_time.is_null());
 270
 271   // Note: the comparison is correct due to the fact that the PendingTask
 272   // operator inverts its comparison operation in order to work well in a heap
 273   // based priority queue.
 274   return oldest_queued_task < *task;
 275 }
 276
 277 bool TaskQueue::ShouldAutoPumpQueueLocked(
 278     const base::PendingTask* previous_task) {
 279   lock_.AssertAcquired();
 280   if (pump_policy_ == TaskQueueManager::PumpPolicy::MANUAL)
 281     return false;
 282   if (pump_policy_ == TaskQueueManager::PumpPolicy::AFTER_WAKEUP &&
 283       TaskIsOlderThanQueuedTasks(previous_task))
 284     return false;
 285   if (incoming_queue_.empty())
 286     return false;
 287   return true;
 288 }
 289
 290 bool TaskQueue::NextPendingDelayedTaskRunTime(
 291     base::TimeTicks* next_pending_delayed_task) {
 292   base::AutoLock lock(lock_);
 293   if (delayed_task_queue_.empty())
 294     return false;
 295   *next_pending_delayed_task = delayed_task_queue_.top().delayed_run_time;
 296   return true;
 297 }
 298
 299 bool TaskQueue::UpdateWorkQueue(LazyNow* lazy_now,
 300                                 const base::PendingTask* previous_task) {
 301   if (!work_queue_.empty())
 302     return true;
 303
 304   {
 305     base::AutoLock lock(lock_);
 306     if (!ShouldAutoPumpQueueLocked(previous_task))
 307       return false;
 308     MoveReadyDelayedTasksToIncomingQueueLocked(lazy_now);
 309     work_queue_.Swap(&incoming_queue_);
 310     TraceQueueSize(true);
 311     return true;
 312   }
 313 }
 314
 315 base::PendingTask TaskQueue::TakeTaskFromWorkQueue() {
 316   base::PendingTask pending_task = work_queue_.front();
 317   work_queue_.pop();
 318   TraceQueueSize(false);
 319   return pending_task;
 320 }
 321
 322 void TaskQueue::TraceQueueSize(bool is_locked) const {
 323   bool is_tracing;
 324   TRACE_EVENT_CATEGORY_GROUP_ENABLED(disabled_by_default_tracing_category_,
 325                                      &is_tracing);
 326   if (!is_tracing || !name_)
 327     return;
 328   if (!is_locked)
 329     lock_.Acquire();
 330   else
 331     lock_.AssertAcquired();
 332   TRACE_COUNTER1(
 333       disabled_by_default_tracing_category_, name_,
 334       incoming_queue_.size() + work_queue_.size() + delayed_task_queue_.size());
 335   if (!is_locked)
 336     lock_.Release();
 337 }
 338
 339 void TaskQueue::EnqueueTaskLocked(const base::PendingTask& pending_task) {
 340   lock_.AssertAcquired();
 341   if (!task_queue_manager_)
 342     return;
 343   if (pump_policy_ == TaskQueueManager::PumpPolicy::AUTO &&
 344       incoming_queue_.empty())
 345     task_queue_manager_->MaybePostDoWorkOnMainRunner();
 346   incoming_queue_.push(pending_task);
 347
 348   if (!pending_task.delayed_run_time.is_null()) {
 349     // Clear the delayed run time because we've already applied the delay
 350     // before getting here.
 351     incoming_queue_.back().delayed_run_time = base::TimeTicks();
 352   }
 353   TraceQueueSize(true);
 354 }
 355
 356 void TaskQueue::SetPumpPolicy(TaskQueueManager::PumpPolicy pump_policy) {
 357   base::AutoLock lock(lock_);
 358   if (pump_policy == TaskQueueManager::PumpPolicy::AUTO &&
 359       pump_policy_ != TaskQueueManager::PumpPolicy::AUTO) {
 360     PumpQueueLocked();
 361   }
 362   pump_policy_ = pump_policy;
 363 }
 364
 365 void TaskQueue::PumpQueueLocked() {
 366   lock_.AssertAcquired();
 367   if (task_queue_manager_) {
 368     LazyNow lazy_now(task_queue_manager_);
 369     MoveReadyDelayedTasksToIncomingQueueLocked(&lazy_now);
 370   }
 371   while (!incoming_queue_.empty()) {
 372     work_queue_.push(incoming_queue_.front());
 373     incoming_queue_.pop();
 374   }
 375   if (!work_queue_.empty())
 376     task_queue_manager_->MaybePostDoWorkOnMainRunner();
 377 }
 378
 379 void TaskQueue::PumpQueue() {
 380   base::AutoLock lock(lock_);
 381   PumpQueueLocked();
 382 }
 383
 384 void TaskQueue::AsValueInto(base::trace_event::TracedValue* state) const {
 385   base::AutoLock lock(lock_);
 386   state->BeginDictionary();
 387   if (name_)
 388     state->SetString("name", name_);
 389   state->SetString("pump_policy", PumpPolicyToString(pump_policy_));
 390   state->BeginArray("incoming_queue");
 391   QueueAsValueInto(incoming_queue_, state);
 392   state->EndArray();
 393   state->BeginArray("work_queue");
 394   QueueAsValueInto(work_queue_, state);
 395   state->EndArray();
 396   state->BeginArray("delayed_task_queue");
 397   QueueAsValueInto(delayed_task_queue_, state);
 398   state->EndArray();
 399   state->EndDictionary();
 400 }
 401
 402 // static
 403 const char* TaskQueue::PumpPolicyToString(
 404     TaskQueueManager::PumpPolicy pump_policy) {
 405   switch (pump_policy) {
 406     case TaskQueueManager::PumpPolicy::AUTO:
 407       return "auto";
 408     case TaskQueueManager::PumpPolicy::AFTER_WAKEUP:
 409       return "after_wakeup";
 410     case TaskQueueManager::PumpPolicy::MANUAL:
 411       return "manual";
 412     default:
 413       NOTREACHED();
 414       return nullptr;
 415   }
 416 }
 417
 418 // static
 419 void TaskQueue::QueueAsValueInto(const base::TaskQueue& queue,
 420                                  base::trace_event::TracedValue* state) {
 421   base::TaskQueue queue_copy(queue);
 422   while (!queue_copy.empty()) {
 423     TaskAsValueInto(queue_copy.front(), state);
 424     queue_copy.pop();
 425   }
 426 }
 427
 428 // static
 429 void TaskQueue::QueueAsValueInto(const base::DelayedTaskQueue& queue,
 430                                  base::trace_event::TracedValue* state) {
 431   base::DelayedTaskQueue queue_copy(queue);
 432   while (!queue_copy.empty()) {
 433     TaskAsValueInto(queue_copy.top(), state);
 434     queue_copy.pop();
 435   }
 436 }
 437
 438 // static
 439 void TaskQueue::TaskAsValueInto(const base::PendingTask& task,
 440                                 base::trace_event::TracedValue* state) {
 441   state->BeginDictionary();
 442   state->SetString("posted_from", task.posted_from.ToString());
 443   state->SetInteger("sequence_num", task.sequence_num);
 444   state->SetBoolean("nestable", task.nestable);
 445   state->SetBoolean("is_high_res", task.is_high_res);
 446   state->SetDouble(
 447       "delayed_run_time",
 448       (task.delayed_run_time - base::TimeTicks()).InMicroseconds() / 1000.0L);
 449   state->EndDictionary();
 450 }
 451
 452 }  // namespace internal
 453
 454 TaskQueueManager::TaskQueueManager(
 455     size_t task_queue_count,
 456     scoped_refptr<NestableSingleThreadTaskRunner> main_task_runner,
 457     TaskQueueSelector* selector,
 458     const char* disabled_by_default_tracing_category)
 459     : main_task_runner_(main_task_runner),
 460       selector_(selector),
 461       pending_dowork_count_(0),
 462       work_batch_size_(1),
 463       time_source_(nullptr),
 464       disabled_by_default_tracing_category_(
 465           disabled_by_default_tracing_category),
 466       deletion_sentinel_(new DeletionSentinel()),
 467       weak_factory_(this) {
 468   DCHECK(main_task_runner->RunsTasksOnCurrentThread());
 469   TRACE_EVENT_OBJECT_CREATED_WITH_ID(disabled_by_default_tracing_category,
 470                                      "TaskQueueManager", this);
 471
 472   for (size_t i = 0; i < task_queue_count; i++) {
 473     scoped_refptr<internal::TaskQueue> queue(make_scoped_refptr(
 474         new internal::TaskQueue(this, disabled_by_default_tracing_category)));
 475     queues_.push_back(queue);
 476   }
 477
 478   std::vector<const base::TaskQueue*> work_queues;
 479   for (const auto& queue : queues_)
 480     work_queues.push_back(&queue->work_queue());
 481   selector_->RegisterWorkQueues(work_queues);
 482
 483   do_work_from_main_thread_closure_ =
 484       base::Bind(&TaskQueueManager::DoWork, weak_factory_.GetWeakPtr(), true);
 485   do_work_from_other_thread_closure_ =
 486       base::Bind(&TaskQueueManager::DoWork, weak_factory_.GetWeakPtr(), false);
 487 }
 488
 489 TaskQueueManager::~TaskQueueManager() {
 490   TRACE_EVENT_OBJECT_DELETED_WITH_ID(disabled_by_default_tracing_category_,
 491                                      "TaskQueueManager", this);
 492   for (auto& queue : queues_)
 493     queue->WillDeleteTaskQueueManager();
 494 }
 495
 496 internal::TaskQueue* TaskQueueManager::Queue(size_t queue_index) const {
 497   DCHECK_LT(queue_index, queues_.size());
 498   return queues_[queue_index].get();
 499 }
 500
 501 scoped_refptr<base::SingleThreadTaskRunner>
 502 TaskQueueManager::TaskRunnerForQueue(size_t queue_index) const {
 503   return Queue(queue_index);
 504 }
 505
 506 bool TaskQueueManager::IsQueueEmpty(size_t queue_index) const {
 507   internal::TaskQueue* queue = Queue(queue_index);
 508   return queue->IsQueueEmpty();
 509 }
 510
 511 base::TimeTicks TaskQueueManager::NextPendingDelayedTaskRunTime() {
 512   DCHECK(main_thread_checker_.CalledOnValidThread());
 513   bool found_pending_task = false;
 514   base::TimeTicks next_pending_delayed_task(
 515       base::TimeTicks::FromInternalValue(kMaxTimeTicks));
 516   for (auto& queue : queues_) {
 517     base::TimeTicks queues_next_pending_delayed_task;
 518     if (queue->NextPendingDelayedTaskRunTime(
 519             &queues_next_pending_delayed_task)) {
 520       found_pending_task = true;
 521       next_pending_delayed_task =
 522           std::min(next_pending_delayed_task, queues_next_pending_delayed_task);
 523     }
 524   }
 525
 526   if (!found_pending_task)
 527     return base::TimeTicks();
 528
 529   DCHECK_NE(next_pending_delayed_task,
 530             base::TimeTicks::FromInternalValue(kMaxTimeTicks));
 531   return next_pending_delayed_task;
 532 }
 533
 534 void TaskQueueManager::SetPumpPolicy(size_t queue_index,
 535                                      PumpPolicy pump_policy) {
 536   DCHECK(main_thread_checker_.CalledOnValidThread());
 537   internal::TaskQueue* queue = Queue(queue_index);
 538   queue->SetPumpPolicy(pump_policy);
 539 }
 540
 541 void TaskQueueManager::PumpQueue(size_t queue_index) {
 542   DCHECK(main_thread_checker_.CalledOnValidThread());
 543   internal::TaskQueue* queue = Queue(queue_index);
 544   queue->PumpQueue();
 545 }
 546
 547 bool TaskQueueManager::UpdateWorkQueues(
 548     const base::PendingTask* previous_task) {
 549   // TODO(skyostil): This is not efficient when the number of queues grows very
 550   // large due to the number of locks taken. Consider optimizing when we get
 551   // there.
 552   DCHECK(main_thread_checker_.CalledOnValidThread());
 553   internal::LazyNow lazy_now(this);
 554   bool has_work = false;
 555   for (auto& queue : queues_) {
 556     has_work |= queue->UpdateWorkQueue(&lazy_now, previous_task);
 557     if (!queue->work_queue().empty()) {
 558       // Currently we should not be getting tasks with delayed run times in any
 559       // of the work queues.
 560       DCHECK(queue->work_queue().front().delayed_run_time.is_null());
 561     }
 562   }
 563   return has_work;
 564 }
 565
 566 void TaskQueueManager::MaybePostDoWorkOnMainRunner() {
 567   bool on_main_thread = main_task_runner_->BelongsToCurrentThread();
 568   if (on_main_thread) {
 569     // We only want one pending DoWork posted from the main thread, or we risk
 570     // an explosion of pending DoWorks which could starve out everything else.
 571     if (pending_dowork_count_ > 0) {
 572       return;
 573     }
 574     pending_dowork_count_++;
 575     main_task_runner_->PostTask(FROM_HERE, do_work_from_main_thread_closure_);
 576   } else {
 577     main_task_runner_->PostTask(FROM_HERE, do_work_from_other_thread_closure_);
 578   }
 579 }
 580
 581 void TaskQueueManager::DoWork(bool posted_from_main_thread) {
 582   if (posted_from_main_thread) {
 583     pending_dowork_count_--;
 584     DCHECK_GE(pending_dowork_count_, 0);
 585   }
 586   DCHECK(main_thread_checker_.CalledOnValidThread());
 587
 588   // Pass nullptr to UpdateWorkQueues here to prevent waking up a
 589   // pump-after-wakeup queue.
 590   if (!UpdateWorkQueues(nullptr))
 591     return;
 592
 593   base::PendingTask previous_task((tracked_objects::Location()),
 594                                   (base::Closure()));
 595   for (int i = 0; i < work_batch_size_; i++) {
 596     size_t queue_index;
 597     if (!SelectWorkQueueToService(&queue_index))
 598       return;
 599     // Note that this function won't post another call to DoWork if one is
 600     // already pending, so it is safe to call it in a loop.
 601     MaybePostDoWorkOnMainRunner();
 602
 603     if (ProcessTaskFromWorkQueue(queue_index, i > 0, &previous_task))
 604       return; // The TaskQueueManager got deleted, we must bail out.
 605
 606     if (!UpdateWorkQueues(&previous_task))
 607       return;
 608   }
 609 }
 610
 611 bool TaskQueueManager::SelectWorkQueueToService(size_t* out_queue_index) {
 612   bool should_run = selector_->SelectWorkQueueToService(out_queue_index);
 613   TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(
 614       disabled_by_default_tracing_category_, "TaskQueueManager", this,
 615       AsValueWithSelectorResult(should_run, *out_queue_index));
 616   return should_run;
 617 }
 618
 619 void TaskQueueManager::DidQueueTask(base::PendingTask* pending_task) {
 620   pending_task->sequence_num = task_sequence_num_.GetNext();
 621   task_annotator_.DidQueueTask("TaskQueueManager::PostTask", *pending_task);
 622 }
 623
 624 bool TaskQueueManager::ProcessTaskFromWorkQueue(
 625     size_t queue_index,
 626     bool has_previous_task,
 627     base::PendingTask* previous_task) {
 628   DCHECK(main_thread_checker_.CalledOnValidThread());
 629   scoped_refptr<DeletionSentinel> protect(deletion_sentinel_);
 630   internal::TaskQueue* queue = Queue(queue_index);
 631   base::PendingTask pending_task = queue->TakeTaskFromWorkQueue();
 632   if (!pending_task.nestable && main_task_runner_->IsNested()) {
 633     // Defer non-nestable work to the main task runner.  NOTE these tasks can be
 634     // arbitrarily delayed so the additional delay should not be a problem.
 635     main_task_runner_->PostNonNestableTask(pending_task.posted_from,
 636                                            pending_task.task);
 637   } else {
 638     // Suppress "will" task observer notifications for the first and "did"
 639     // notifications for the last task in the batch to avoid duplicate
 640     // notifications.
 641     if (has_previous_task) {
 642       FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,
 643                         DidProcessTask(*previous_task));
 644       FOR_EACH_OBSERVER(base::MessageLoop::TaskObserver, task_observers_,
 645                         WillProcessTask(pending_task));
 646     }
 647     task_annotator_.RunTask("TaskQueueManager::PostTask",
 648                             "TaskQueueManager::RunTask", pending_task);
 649
 650     // Detect if the TaskQueueManager just got deleted.  If this happens we must
 651     // not access any member variables after this point.
 652     if (protect->HasOneRef())
 653       return true;
 654
 655     pending_task.task.Reset();
 656     *previous_task = pending_task;
 657   }
 658   return false;
 659 }
 660
 661 bool TaskQueueManager::RunsTasksOnCurrentThread() const {
 662   return main_task_runner_->RunsTasksOnCurrentThread();
 663 }
 664
 665 bool TaskQueueManager::PostDelayedTask(
 666     const tracked_objects::Location& from_here,
 667     const base::Closure& task,
 668     base::TimeDelta delay) {
 669   DCHECK(delay > base::TimeDelta());
 670   return main_task_runner_->PostDelayedTask(from_here, task, delay);
 671 }
 672
 673 void TaskQueueManager::SetQueueName(size_t queue_index, const char* name) {
 674   DCHECK(main_thread_checker_.CalledOnValidThread());
 675   internal::TaskQueue* queue = Queue(queue_index);
 676   queue->set_name(name);
 677 }
 678
 679 void TaskQueueManager::SetWorkBatchSize(int work_batch_size) {
 680   DCHECK(main_thread_checker_.CalledOnValidThread());
 681   DCHECK_GE(work_batch_size, 1);
 682   work_batch_size_ = work_batch_size;
 683 }
 684
 685 void TaskQueueManager::AddTaskObserver(
 686     base::MessageLoop::TaskObserver* task_observer) {
 687   DCHECK(main_thread_checker_.CalledOnValidThread());
 688   base::MessageLoop::current()->AddTaskObserver(task_observer);
 689   task_observers_.AddObserver(task_observer);
 690 }
 691
 692 void TaskQueueManager::RemoveTaskObserver(
 693     base::MessageLoop::TaskObserver* task_observer) {
 694   DCHECK(main_thread_checker_.CalledOnValidThread());
 695   base::MessageLoop::current()->RemoveTaskObserver(task_observer);
 696   task_observers_.RemoveObserver(task_observer);
 697 }
 698
 699 void TaskQueueManager::SetTimeSourceForTesting(
 700     scoped_refptr<cc::TestNowSource> time_source) {
 701   DCHECK(main_thread_checker_.CalledOnValidThread());
 702   time_source_ = time_source;
 703 }
 704
 705 base::TimeTicks TaskQueueManager::Now() const {
 706   return UNLIKELY(time_source_) ? time_source_->Now() : base::TimeTicks::Now();
 707 }
 708
 709 scoped_refptr<base::trace_event::ConvertableToTraceFormat>
 710 TaskQueueManager::AsValueWithSelectorResult(bool should_run,
 711                                             size_t selected_queue) const {
 712   DCHECK(main_thread_checker_.CalledOnValidThread());
 713   scoped_refptr<base::trace_event::TracedValue> state =
 714       new base::trace_event::TracedValue();
 715   state->BeginArray("queues");
 716   for (auto& queue : queues_)
 717     queue->AsValueInto(state.get());
 718   state->EndArray();
 719   state->BeginDictionary("selector");
 720   selector_->AsValueInto(state.get());
 721   state->EndDictionary();
 722   if (should_run)
 723     state->SetInteger("selected_queue", selected_queue);
 724   return state;
 725 }
 726
 727 }  // namespace content