blob: 970b0d2598da973e2aae3f041e5a6c995ad27eea [file] [log] [blame]
// Copyright 2015 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 <stddef.h>
#include <memory>
#include <set>
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/weak_ptr.h"
#include "base/message_loop/message_loop.h"
#include "base/pending_task.h"
#include "base/threading/thread_checker.h"
#include "base/trace_event/trace_event.h"
#include "base/trace_event/trace_event_argument.h"
#include "platform/scheduler/base/enqueue_order.h"
#include "platform/scheduler/base/graceful_queue_shutdown_helper.h"
#include "platform/scheduler/base/intrusive_heap.h"
#include "platform/scheduler/base/sequence.h"
#include "platform/scheduler/base/task_queue.h"
#include "platform/wtf/Deque.h"
namespace blink {
namespace scheduler {
class LazyNow;
class TimeDomain;
class TaskQueueManager;
namespace internal {
class WorkQueue;
class WorkQueueSets;
// TaskQueueImpl has four main queues:
// Immediate (non-delayed) tasks:
// immediate_incoming_queue - PostTask enqueues tasks here
// immediate_work_queue
// Delayed tasks
// delayed_incoming_queue - PostDelayedTask enqueues tasks here
// delayed_work_queue
// The immediate_incoming_queue can be accessed from any thread, the other
// queues are main-thread only. To reduce the overhead of locking,
// immediate_work_queue is swapped with immediate_incoming_queue when
// immediate_work_queue becomes empty.
// Delayed tasks are initially posted to delayed_incoming_queue and a wake-up
// is scheduled with the TimeDomain. When the delay has elapsed, the TimeDomain
// calls UpdateDelayedWorkQueue and ready delayed tasks are moved into the
// delayed_work_queue. Note the EnqueueOrder (used for ordering) for a delayed
// task is not set until it's moved into the delayed_work_queue.
// TaskQueueImpl uses the WorkQueueSets and the TaskQueueSelector to implement
// prioritization. Task selection is done by the TaskQueueSelector and when a
// queue is selected, it round-robins between the immediate_work_queue and
// delayed_work_queue. The reason for this is we want to make sure delayed
// tasks (normally the most common type) don't starve out immediate work.
class PLATFORM_EXPORT TaskQueueImpl {
TaskQueueImpl(TaskQueueManager* task_queue_manager,
TimeDomain* time_domain,
const TaskQueue::Spec& spec);
// Represents a time at which a task wants to run. Tasks scheduled for the
// same point in time will be ordered by their sequence numbers.
struct DelayedWakeUp {
base::TimeTicks time;
int sequence_num;
bool operator<=(const DelayedWakeUp& other) const {
if (time == other.time) {
// Debug gcc builds can compare an element against itself.
DCHECK(sequence_num != other.sequence_num || this == &other);
return (sequence_num - other.sequence_num) < 0;
return time < other.time;
class PLATFORM_EXPORT Task : public TaskQueue::Task {
Task(TaskQueue::PostedTask task,
base::TimeTicks desired_run_time,
EnqueueOrder sequence_number);
Task(TaskQueue::PostedTask task,
base::TimeTicks desired_run_time,
EnqueueOrder sequence_number,
EnqueueOrder enqueue_order);
DelayedWakeUp delayed_wake_up() const {
return DelayedWakeUp{delayed_run_time, sequence_num};
EnqueueOrder enqueue_order() const {
#ifndef NDEBUG
return enqueue_order_;
void set_enqueue_order(EnqueueOrder enqueue_order) {
#ifndef NDEBUG
enqueue_order_set_ = true;
enqueue_order_ = enqueue_order;
#ifndef NDEBUG
bool enqueue_order_set() const { return enqueue_order_set_; }
#ifndef NDEBUG
bool enqueue_order_set_;
// Similar to sequence number, but ultimately the |enqueue_order_| is what
// the scheduler uses for task ordering. For immediate tasks |enqueue_order|
// is set when posted, but for delayed tasks it's not defined until they are
// enqueued on the |delayed_work_queue_|. This is because otherwise delayed
// tasks could run before an immediate task posted after the delayed task.
EnqueueOrder enqueue_order_;
// A result retuned by PostDelayedTask. When scheduler failed to post a task
// due to being shutdown a task is returned to be destroyed outside the lock.
struct PostTaskResult {
PostTaskResult(bool success, TaskQueue::PostedTask task);
static PostTaskResult Success();
static PostTaskResult Fail(TaskQueue::PostedTask task);
bool success = false;
TaskQueue::PostedTask task;
using OnNextWakeUpChangedCallback = base::Callback<void(base::TimeTicks)>;
using OnTaskStartedHandler =
base::RepeatingCallback<void(const TaskQueue::Task&, base::TimeTicks)>;
using OnTaskCompletedHandler =
base::RepeatingCallback<void(const TaskQueue::Task&,
// TaskQueue implementation.
const char* GetName() const;
bool RunsTasksInCurrentSequence() const;
PostTaskResult PostDelayedTask(TaskQueue::PostedTask task);
// Require a reference to enclosing task queue for lifetime control.
std::unique_ptr<TaskQueue::QueueEnabledVoter> CreateQueueEnabledVoter(
scoped_refptr<TaskQueue> owning_task_queue);
bool IsQueueEnabled() const;
bool IsEmpty() const;
size_t GetNumberOfPendingTasks() const;
bool HasTaskToRunImmediately() const;
base::Optional<base::TimeTicks> GetNextScheduledWakeUp();
void SetQueuePriority(TaskQueue::QueuePriority priority);
TaskQueue::QueuePriority GetQueuePriority() const;
void AddTaskObserver(base::MessageLoop::TaskObserver* task_observer);
void RemoveTaskObserver(base::MessageLoop::TaskObserver* task_observer);
void SetTimeDomain(TimeDomain* time_domain);
TimeDomain* GetTimeDomain() const;
void SetBlameContext(base::trace_event::BlameContext* blame_context);
void InsertFence(TaskQueue::InsertFencePosition position);
void InsertFenceAt(base::TimeTicks time);
void RemoveFence();
bool HasActiveFence();
bool BlockedByFence() const;
// Implementation of TaskQueue::SetObserver.
void SetOnNextWakeUpChangedCallback(OnNextWakeUpChangedCallback callback);
void UnregisterTaskQueue();
// Returns true if a (potentially hypothetical) task with the specified
// |enqueue_order| could run on the queue. Must be called from the main
// thread.
bool CouldTaskRun(EnqueueOrder enqueue_order) const;
// Must only be called from the thread this task queue was created on.
void ReloadImmediateWorkQueueIfEmpty();
void AsValueInto(base::TimeTicks now,
base::trace_event::TracedValue* state) const;
bool GetQuiescenceMonitored() const { return should_monitor_quiescence_; }
bool GetShouldNotifyObservers() const { return should_notify_observers_; }
void NotifyWillProcessTask(const base::PendingTask& pending_task);
void NotifyDidProcessTask(const base::PendingTask& pending_task);
// Called by TimeDomain when the wake-up for this queue has changed.
// There is only one wake-up, new wake-up cancels any previous wake-ups.
// If |scheduled_time_domain_wake_up| is base::nullopt then the wake-up
// has been cancelled.
// Must be called from the main thread.
void SetScheduledTimeDomainWakeUp(
base::Optional<base::TimeTicks> scheduled_time_domain_wake_up);
// Check for available tasks in immediate work queues.
// Used to check if we need to generate notifications about delayed work.
bool HasPendingImmediateWork();
WorkQueue* delayed_work_queue() {
return main_thread_only().delayed_work_queue.get();
const WorkQueue* delayed_work_queue() const {
return main_thread_only().delayed_work_queue.get();
WorkQueue* immediate_work_queue() {
return main_thread_only().immediate_work_queue.get();
const WorkQueue* immediate_work_queue() const {
return main_thread_only().immediate_work_queue.get();
bool should_report_when_execution_blocked() const {
return should_report_when_execution_blocked_;
// Enqueues any delayed tasks which should be run now on the
// |delayed_work_queue|. Returns the subsequent wake-up that is required, if
// any. Must be called from the main thread.
base::Optional<DelayedWakeUp> WakeUpForDelayedWork(LazyNow* lazy_now);
base::Optional<base::TimeTicks> scheduled_time_domain_wake_up() const {
return main_thread_only().scheduled_time_domain_wake_up;
HeapHandle heap_handle() const { return main_thread_only().heap_handle; }
void set_heap_handle(HeapHandle heap_handle) {
main_thread_only().heap_handle = heap_handle;
// Pushes |task| onto the front of the specified work queue. Caution must be
// taken with this API because you could easily starve out other work.
void RequeueDeferredNonNestableTask(TaskQueueImpl::Task&& task,
Sequence::WorkType work_type);
void PushImmediateIncomingTaskForTest(TaskQueueImpl::Task&& task);
EnqueueOrder GetFenceForTest() const;
class QueueEnabledVoterImpl : public TaskQueue::QueueEnabledVoter {
explicit QueueEnabledVoterImpl(scoped_refptr<TaskQueue> task_queue);
~QueueEnabledVoterImpl() override;
// QueueEnabledVoter implementation.
void SetQueueEnabled(bool enabled) override;
TaskQueueImpl* GetTaskQueueForTest() const {
return task_queue_->GetTaskQueueImpl();
friend class TaskQueueImpl;
scoped_refptr<TaskQueue> task_queue_;
bool enabled_;
// Iterates over |delayed_incoming_queue| removing canceled tasks.
void SweepCanceledDelayedTasks(base::TimeTicks now);
// Allows wrapping TaskQueue to set a handler to subscribe for notifications
// about started and completed tasks.
void SetOnTaskStartedHandler(OnTaskStartedHandler handler);
void OnTaskStarted(const TaskQueue::Task& task, base::TimeTicks start);
void SetOnTaskCompletedHandler(OnTaskCompletedHandler handler);
void OnTaskCompleted(const TaskQueue::Task& task,
base::TimeTicks start,
base::TimeTicks end,
base::Optional<base::TimeDelta> thread_time);
bool RequiresTaskTiming() const;
base::WeakPtr<TaskQueueManager> GetTaskQueueManagerWeakPtr();
scoped_refptr<GracefulQueueShutdownHelper> GetGracefulQueueShutdownHelper();
// Returns true if this queue is unregistered or task queue manager is deleted
// and this queue can be safely deleted on any thread.
bool IsUnregistered() const;
// Disables queue for testing purposes, when a QueueEnabledVoter can't be
// constructed due to not having TaskQueue.
void SetQueueEnabledForTest(bool enabled);
friend class WorkQueue;
friend class WorkQueueTest;
struct AnyThread {
AnyThread(TaskQueueManager* task_queue_manager, TimeDomain* time_domain);
// TaskQueueManager, TimeDomain and Observer are maintained in two copies:
// inside AnyThread and inside MainThreadOnly. They can be changed only from
// main thread, so it should be locked before accessing from other threads.
TaskQueueManager* task_queue_manager;
TimeDomain* time_domain;
// Callback corresponding to TaskQueue::Observer::OnQueueNextChanged.
OnNextWakeUpChangedCallback on_next_wake_up_changed_callback;
struct MainThreadOnly {
MainThreadOnly(TaskQueueManager* task_queue_manager,
TaskQueueImpl* task_queue,
TimeDomain* time_domain);
// Another copy of TaskQueueManager, TimeDomain and Observer
// for lock-free access from the main thread.
// See description inside struct AnyThread for details.
TaskQueueManager* task_queue_manager;
TimeDomain* time_domain;
// Callback corresponding to TaskQueue::Observer::OnQueueNextChanged.
OnNextWakeUpChangedCallback on_next_wake_up_changed_callback;
std::unique_ptr<WorkQueue> delayed_work_queue;
std::unique_ptr<WorkQueue> immediate_work_queue;
std::priority_queue<Task> delayed_incoming_queue;
base::ObserverList<base::MessageLoop::TaskObserver> task_observers;
size_t set_index;
HeapHandle heap_handle;
int is_enabled_refcount;
int voter_refcount;
base::trace_event::BlameContext* blame_context; // Not owned.
EnqueueOrder current_fence;
base::Optional<base::TimeTicks> delayed_fence;
base::Optional<base::TimeTicks> scheduled_time_domain_wake_up;
OnTaskStartedHandler on_task_started_handler;
OnTaskCompletedHandler on_task_completed_handler;
// If false, queue will be disabled. Used only for tests.
bool is_enabled_for_test;
PostTaskResult PostImmediateTaskImpl(TaskQueue::PostedTask task);
PostTaskResult PostDelayedTaskImpl(TaskQueue::PostedTask task);
// Push the task onto the |delayed_incoming_queue|. Lock-free main thread
// only fast path.
void PushOntoDelayedIncomingQueueFromMainThread(Task pending_task,
base::TimeTicks now);
// Push the task onto the |delayed_incoming_queue|. Slow path from other
// threads.
void PushOntoDelayedIncomingQueueLocked(Task pending_task);
void ScheduleDelayedWorkTask(Task pending_task);
void MoveReadyImmediateTasksToImmediateWorkQueueLocked();
// Push the task onto the |immediate_incoming_queue| and for auto pumped
// queues it calls MaybePostDoWorkOnMainRunner if the Incoming queue was
// empty.
void PushOntoImmediateIncomingQueueLocked(Task task);
// We reserve an inline capacity of 8 tasks to try and reduce the load on
// PartitionAlloc.
using TaskDeque = WTF::Deque<Task, 8>;
// Extracts all the tasks from the immediate incoming queue and clears it.
// Can be called from any thread.
TaskDeque TakeImmediateIncomingQueue();
void TraceQueueSize() const;
static void QueueAsValueInto(const TaskDeque& queue,
base::TimeTicks now,
base::trace_event::TracedValue* state);
static void QueueAsValueInto(const std::priority_queue<Task>& queue,
base::TimeTicks now,
base::trace_event::TracedValue* state);
static void TaskAsValueInto(const Task& task,
base::TimeTicks now,
base::trace_event::TracedValue* state);
void RemoveQueueEnabledVoter(const QueueEnabledVoterImpl* voter);
void OnQueueEnabledVoteChanged(bool enabled);
void EnableOrDisableWithSelector(bool enable);
// Schedules delayed work on time domain and calls the observer.
void ScheduleDelayedWorkInTimeDomain(base::TimeTicks now);
// Activate a delayed fence if a time has come.
void ActivateDelayedFenceIfNeeded(base::TimeTicks now);
const char* name_;
const base::PlatformThreadId thread_id_;
mutable base::Lock any_thread_lock_;
AnyThread any_thread_;
struct AnyThread& any_thread() {
return any_thread_;
const struct AnyThread& any_thread() const {
return any_thread_;
base::ThreadChecker main_thread_checker_;
MainThreadOnly main_thread_only_;
MainThreadOnly& main_thread_only() {
return main_thread_only_;
const MainThreadOnly& main_thread_only() const {
return main_thread_only_;
mutable base::Lock immediate_incoming_queue_lock_;
TaskDeque immediate_incoming_queue_;
TaskDeque& immediate_incoming_queue() {
return immediate_incoming_queue_;
const TaskDeque& immediate_incoming_queue() const {
return immediate_incoming_queue_;
const bool should_monitor_quiescence_;
const bool should_notify_observers_;
const bool should_report_when_execution_blocked_;
} // namespace internal
} // namespace scheduler
} // namespace blink