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// Copyright 2018 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 <list>
#include <map>
#include <memory>
#include <random>
#include <set>
#include <unordered_map>
#include <utility>
#include <vector>
#include "base/atomic_sequence_num.h"
#include "base/cancelable_callback.h"
#include "base/containers/circular_deque.h"
#include "base/debug/task_annotator.h"
#include "base/macros.h"
#include "base/memory/scoped_refptr.h"
#include "base/memory/weak_ptr.h"
#include "base/message_loop/message_loop.h"
#include "base/pending_task.h"
#include "base/run_loop.h"
#include "base/single_thread_task_runner.h"
#include "base/synchronization/lock.h"
#include "base/task/sequence_manager/associated_thread_id.h"
#include "base/task/sequence_manager/enqueue_order.h"
#include "base/task/sequence_manager/graceful_queue_shutdown_helper.h"
#include "base/task/sequence_manager/moveable_auto_lock.h"
#include "base/task/sequence_manager/sequence_manager.h"
#include "base/task/sequence_manager/task_queue_impl.h"
#include "base/task/sequence_manager/task_queue_selector.h"
#include "base/task/sequence_manager/thread_controller.h"
#include "base/threading/thread_checker.h"
namespace base {
namespace debug {
struct CrashKeyString;
} // namespace debug
namespace trace_event {
class ConvertableToTraceFormat;
} // namespace trace_event
namespace sequence_manager {
class SequenceManagerForTest;
class TaskQueue;
class TaskTimeObserver;
class TimeDomain;
namespace internal {
class RealTimeDomain;
class TaskQueueImpl;
// The task queue manager provides N task queues and a selector interface for
// choosing which task queue to service next. Each task queue consists of two
// sub queues:
// 1. Incoming task queue. Tasks that are posted get immediately appended here.
// When a task is appended into an empty incoming queue, the task manager
// work function (DoWork()) is scheduled to run on the main task runner.
// 2. Work queue. If a work queue is empty when DoWork() is entered, tasks from
// the incoming task queue (if any) are moved here. The work queues are
// registered with the selector as input to the scheduling decision.
class BASE_EXPORT SequenceManagerImpl
: public SequenceManager,
public internal::SequencedTaskSource,
public internal::TaskQueueSelector::Observer,
public RunLoop::NestingObserver {
using Observer = SequenceManager::Observer;
~SequenceManagerImpl() override;
// Assume direct control over current thread and create a SequenceManager.
// This function should be called only once per thread.
// This function assumes that a MessageLoop is initialized for
// the current thread.
static std::unique_ptr<SequenceManagerImpl> CreateOnCurrentThread();
// Create a SequenceManager for a future thread that will run the provided
// MessageLoop. The SequenceManager can be initialized on the current thread
// and then needs to be bound and initialized on the target thread by calling
// BindToCurrentThread() and CompleteInitializationOnBoundThread() during the
// thread's startup. If |message_loop| is null then BindToMessageLoop() must
// be called instead of CompleteInitializationOnBoundThread.
// This function should be called only once per MessageLoop.
static std::unique_ptr<SequenceManagerImpl> CreateUnbound(
MessageLoop* message_loop);
// SequenceManager implementation:
void BindToCurrentThread() override;
void BindToMessageLoop(MessageLoop* message_loop) override;
void CompleteInitializationOnBoundThread() override;
void SetObserver(Observer* observer) override;
void AddTaskObserver(MessageLoop::TaskObserver* task_observer) override;
void RemoveTaskObserver(MessageLoop::TaskObserver* task_observer) override;
void AddTaskTimeObserver(TaskTimeObserver* task_time_observer) override;
void RemoveTaskTimeObserver(TaskTimeObserver* task_time_observer) override;
void RegisterTimeDomain(TimeDomain* time_domain) override;
void UnregisterTimeDomain(TimeDomain* time_domain) override;
TimeDomain* GetRealTimeDomain() const override;
const TickClock* GetTickClock() const override;
TimeTicks NowTicks() const override;
void SetDefaultTaskRunner(
scoped_refptr<SingleThreadTaskRunner> task_runner) override;
void SweepCanceledDelayedTasks() override;
bool GetAndClearSystemIsQuiescentBit() override;
void SetWorkBatchSize(int work_batch_size) override;
void SetTimerSlack(TimerSlack timer_slack) override;
void EnableCrashKeys(const char* file_name_crash_key,
const char* function_name_crash_key) override;
const MetricRecordingSettings& GetMetricRecordingSettings() const override;
// Implementation of SequencedTaskSource:
Optional<PendingTask> TakeTask() override;
void DidRunTask() override;
TimeDelta DelayTillNextTask(LazyNow* lazy_now) override;
// Requests that a task to process work is posted on the main task runner.
// These tasks are de-duplicated in two buckets: main-thread and all other
// threads. This distinction is done to reduce the overhead from locks, we
// assume the main-thread path will be hot.
void MaybeScheduleImmediateWork(const Location& from_here);
// Requests that a delayed task to process work is posted on the main task
// runner. These delayed tasks are de-duplicated. Must be called on the thread
// this class was created on.
// Schedules next wake-up at the given time, cancels any previous requests.
// Use TimeTicks::Max() to cancel a wake-up.
// Must be called from a TimeDomain only.
void SetNextDelayedDoWork(LazyNow* lazy_now, TimeTicks run_time);
// Returns the currently executing TaskQueue if any. Must be called on the
// thread this class was created on.
internal::TaskQueueImpl* currently_executing_task_queue() const;
// Unregisters a TaskQueue previously created by |NewTaskQueue()|.
// No tasks will run on this queue after this call.
void UnregisterTaskQueueImpl(
std::unique_ptr<internal::TaskQueueImpl> task_queue);
GetGracefulQueueShutdownHelper() const;
const scoped_refptr<AssociatedThreadId>& associated_thread() const {
return associated_thread_;
WeakPtr<SequenceManagerImpl> GetWeakPtr();
// TODO(alexclarke): Remove when possible.
bool SetCrashKeysAndCheckIsTaskCancelled(const PendingTask& task) const;
// Create a task queue manager where |controller| controls the thread
// on which the tasks are eventually run.
explicit SequenceManagerImpl(
std::unique_ptr<internal::ThreadController> controller);
friend class internal::TaskQueueImpl;
friend class ::base::sequence_manager::SequenceManagerForTest;
enum class ProcessTaskResult {
struct AnyThread {
// Task queues with newly available work on the incoming queue.
internal::IncomingImmediateWorkList* incoming_immediate_work_list = nullptr;
// SequenceManager maintains a queue of non-nestable tasks since they're
// uncommon and allocating an extra deque per TaskQueue will waste the memory.
using NonNestableTaskDeque =
// We have to track rentrancy because we support nested runloops but the
// selector interface is unaware of those. This struct keeps track off all
// task related state needed to make pairs of TakeTask() / DidRunTask() work.
struct ExecutingTask {
ExecutingTask(Task&& task,
internal::TaskQueueImpl* task_queue,
TaskQueue::TaskTiming task_timing)
: pending_task(std::move(task)),
task_type(pending_task.task_type) {}
Task pending_task;
internal::TaskQueueImpl* task_queue = nullptr;
TaskQueue::TaskTiming task_timing;
// Save task metadata to use in after running a task as |pending_task|
// won't be available then.
int task_type;
struct MainThreadOnly {
explicit MainThreadOnly(
const scoped_refptr<AssociatedThreadId>& associated_thread);
int nesting_depth = 0;
NonNestableTaskDeque non_nestable_task_queue;
// TODO(altimin): Switch to instruction pointer crash key when it's
// available.
debug::CrashKeyString* file_name_crash_key = nullptr;
debug::CrashKeyString* function_name_crash_key = nullptr;
std::mt19937_64 random_generator;
std::uniform_real_distribution<double> uniform_distribution;
internal::TaskQueueSelector selector;
ObserverList<MessageLoop::TaskObserver>::Unchecked task_observers;
ObserverList<TaskTimeObserver>::Unchecked task_time_observers;
std::set<TimeDomain*> time_domains;
std::unique_ptr<internal::RealTimeDomain> real_time_domain;
// List of task queues managed by this SequenceManager.
// - active_queues contains queues that are still running tasks.
// Most often they are owned by relevant TaskQueues, but
// queues_to_gracefully_shutdown_ are included here too.
// - queues_to_gracefully_shutdown contains queues which should be deleted
// when they become empty.
// - queues_to_delete contains soon-to-be-deleted queues, because some
// internal scheduling code does not expect queues to be pulled
// from underneath.
std::set<internal::TaskQueueImpl*> active_queues;
std::map<internal::TaskQueueImpl*, std::unique_ptr<internal::TaskQueueImpl>>
std::map<internal::TaskQueueImpl*, std::unique_ptr<internal::TaskQueueImpl>>
// Scratch space used to store the contents of
// any_thread().incoming_immediate_work_list for use by
// ReloadEmptyWorkQueues. We keep hold of this vector to avoid unnecessary
// memory allocations.
std::vector<internal::TaskQueueImpl*> queues_to_reload;
bool task_was_run_on_quiescence_monitored_queue = false;
bool nesting_observer_registered_ = false;
// Due to nested runloops more than one task can be executing concurrently.
std::list<ExecutingTask> task_execution_stack;
Observer* observer = nullptr; // NOT OWNED
// TaskQueueSelector::Observer:
void OnTaskQueueEnabled(internal::TaskQueueImpl* queue) override;
// RunLoop::NestingObserver:
void OnBeginNestedRunLoop() override;
void OnExitNestedRunLoop() override;
// Called by the task queue to inform this SequenceManager of a task that's
// about to be queued. This SequenceManager may use this opportunity to add
// metadata to |pending_task| before it is moved into the queue.
void WillQueueTask(Task* pending_task);
// Delayed Tasks with run_times <= Now() are enqueued onto the work queue and
// reloads any empty work queues.
void WakeUpReadyDelayedQueues(LazyNow* lazy_now);
void NotifyWillProcessTask(ExecutingTask* task, LazyNow* time_before_task);
void NotifyDidProcessTask(ExecutingTask* task, LazyNow* time_after_task);
internal::EnqueueOrder GetNextSequenceNumber();
AsValueWithSelectorResult(bool should_run,
internal::WorkQueue* selected_work_queue) const;
// Adds |queue| to |any_thread().has_incoming_immediate_work_| and if
// |queue_is_blocked| is false it makes sure a DoWork is posted.
// Can be called from any thread.
void OnQueueHasIncomingImmediateWork(internal::TaskQueueImpl* queue,
internal::EnqueueOrder enqueue_order,
bool queue_is_blocked);
// Returns true if |task_queue| was added to the list, or false if it was
// already in the list. If |task_queue| was inserted, the |order| is set
// with |enqueue_order|.
bool AddToIncomingImmediateWorkList(internal::TaskQueueImpl* task_queue,
internal::EnqueueOrder enqueue_order);
void RemoveFromIncomingImmediateWorkList(internal::TaskQueueImpl* task_queue);
// Calls |ReloadImmediateWorkQueueIfEmpty| on all queues in
// |main_thread_only().queues_to_reload|.
void ReloadEmptyWorkQueues();
std::unique_ptr<internal::TaskQueueImpl> CreateTaskQueueImpl(
const TaskQueue::Spec& spec) override;
void TakeQueuesToGracefullyShutdownFromHelper();
// Deletes queues marked for deletion and empty queues marked for shutdown.
void CleanUpQueues();
bool ShouldRecordCPUTimeForTask();
// Helper to terminate all scoped trace events to allow starting new ones
// in TakeTask().
Optional<PendingTask> TakeTaskImpl();
// Determines if wall time or thread time should be recorded for the next
// task.
TaskQueue::TaskTiming InitializeTaskTiming(
internal::TaskQueueImpl* task_queue);
scoped_refptr<AssociatedThreadId> associated_thread_;
const scoped_refptr<internal::GracefulQueueShutdownHelper>
internal::EnqueueOrder::Generator enqueue_order_generator_;
std::unique_ptr<internal::ThreadController> controller_;
mutable Lock any_thread_lock_;
AnyThread any_thread_;
struct AnyThread& any_thread() {
return any_thread_;
const struct AnyThread& any_thread() const {
return any_thread_;
const MetricRecordingSettings metric_recording_settings_;
// A check to bail out early during memory corruption.
bool Validate();
int32_t memory_corruption_sentinel_;
MainThreadOnly main_thread_only_;
MainThreadOnly& main_thread_only() {
return main_thread_only_;
const MainThreadOnly& main_thread_only() const {
return main_thread_only_;
WeakPtrFactory<SequenceManagerImpl> weak_factory_;
} // namespace internal
} // namespace sequence_manager
} // namespace base