| // Copyright 2016 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 "base/task_scheduler/task_tracker.h" |
| |
| #include <limits> |
| #include <string> |
| #include <vector> |
| |
| #include "base/base_switches.h" |
| #include "base/callback.h" |
| #include "base/command_line.h" |
| #include "base/json/json_writer.h" |
| #include "base/memory/ptr_util.h" |
| #include "base/metrics/histogram_macros.h" |
| #include "base/sequence_token.h" |
| #include "base/synchronization/condition_variable.h" |
| #include "base/task_scheduler/scoped_set_task_priority_for_current_thread.h" |
| #include "base/threading/sequence_local_storage_map.h" |
| #include "base/threading/sequenced_task_runner_handle.h" |
| #include "base/threading/thread_restrictions.h" |
| #include "base/threading/thread_task_runner_handle.h" |
| #include "base/time/time.h" |
| #include "base/trace_event/trace_event.h" |
| #include "base/values.h" |
| |
| namespace base { |
| namespace internal { |
| |
| namespace { |
| |
| constexpr char kParallelExecutionMode[] = "parallel"; |
| constexpr char kSequencedExecutionMode[] = "sequenced"; |
| constexpr char kSingleThreadExecutionMode[] = "single thread"; |
| |
| // An immutable copy of a scheduler task's info required by tracing. |
| class TaskTracingInfo : public trace_event::ConvertableToTraceFormat { |
| public: |
| TaskTracingInfo(const TaskTraits& task_traits, |
| const char* execution_mode, |
| const SequenceToken& sequence_token) |
| : task_traits_(task_traits), |
| execution_mode_(execution_mode), |
| sequence_token_(sequence_token) {} |
| |
| // trace_event::ConvertableToTraceFormat implementation. |
| void AppendAsTraceFormat(std::string* out) const override; |
| |
| private: |
| const TaskTraits task_traits_; |
| const char* const execution_mode_; |
| const SequenceToken sequence_token_; |
| |
| DISALLOW_COPY_AND_ASSIGN(TaskTracingInfo); |
| }; |
| |
| void TaskTracingInfo::AppendAsTraceFormat(std::string* out) const { |
| DictionaryValue dict; |
| |
| dict.SetString("task_priority", |
| base::TaskPriorityToString(task_traits_.priority())); |
| dict.SetString("execution_mode", execution_mode_); |
| if (execution_mode_ != kParallelExecutionMode) |
| dict.SetInteger("sequence_token", sequence_token_.ToInternalValue()); |
| |
| std::string tmp; |
| JSONWriter::Write(dict, &tmp); |
| out->append(tmp); |
| } |
| |
| // These name conveys that a Task is posted to/run by the task scheduler without |
| // revealing its implementation details. |
| constexpr char kQueueFunctionName[] = "TaskScheduler PostTask"; |
| constexpr char kRunFunctionName[] = "TaskScheduler RunTask"; |
| |
| constexpr char kTaskSchedulerFlowTracingCategory[] = |
| TRACE_DISABLED_BY_DEFAULT("task_scheduler.flow"); |
| |
| // Constructs a histogram to track latency which is logging to |
| // "TaskScheduler.{histogram_name}.{histogram_label}.{task_type_suffix}". |
| HistogramBase* GetLatencyHistogram(StringPiece histogram_name, |
| StringPiece histogram_label, |
| StringPiece task_type_suffix) { |
| DCHECK(!histogram_name.empty()); |
| DCHECK(!histogram_label.empty()); |
| DCHECK(!task_type_suffix.empty()); |
| // Mimics the UMA_HISTOGRAM_HIGH_RESOLUTION_CUSTOM_TIMES macro. The minimums |
| // and maximums were chosen to place the 1ms mark at around the 70% range |
| // coverage for buckets giving us good info for tasks that have a latency |
| // below 1ms (most of them) and enough info to assess how bad the latency is |
| // for tasks that exceed this threshold. |
| const std::string histogram = JoinString( |
| {"TaskScheduler", histogram_name, histogram_label, task_type_suffix}, |
| "."); |
| return Histogram::FactoryMicrosecondsTimeGet( |
| histogram, TimeDelta::FromMicroseconds(1), |
| TimeDelta::FromMilliseconds(20), 50, |
| HistogramBase::kUmaTargetedHistogramFlag); |
| } |
| |
| // Upper bound for the |
| // TaskScheduler.BlockShutdownTasksPostedDuringShutdown histogram. |
| constexpr HistogramBase::Sample kMaxBlockShutdownTasksPostedDuringShutdown = |
| 1000; |
| |
| void RecordNumBlockShutdownTasksPostedDuringShutdown( |
| HistogramBase::Sample value) { |
| UMA_HISTOGRAM_CUSTOM_COUNTS( |
| "TaskScheduler.BlockShutdownTasksPostedDuringShutdown", value, 1, |
| kMaxBlockShutdownTasksPostedDuringShutdown, 50); |
| } |
| |
| // Returns the maximum number of TaskPriority::BACKGROUND sequences that can be |
| // scheduled concurrently based on command line flags. |
| int GetMaxNumScheduledBackgroundSequences() { |
| // The CommandLine might not be initialized if TaskScheduler is initialized |
| // in a dynamic library which doesn't have access to argc/argv. |
| if (CommandLine::InitializedForCurrentProcess() && |
| CommandLine::ForCurrentProcess()->HasSwitch( |
| switches::kDisableBackgroundTasks)) { |
| return 0; |
| } |
| return std::numeric_limits<int>::max(); |
| } |
| |
| } // namespace |
| |
| // Atomic internal state used by TaskTracker. Sequential consistency shouldn't |
| // be assumed from these calls (i.e. a thread reading |
| // |HasShutdownStarted() == true| isn't guaranteed to see all writes made before |
| // |StartShutdown()| on the thread that invoked it). |
| class TaskTracker::State { |
| public: |
| State() = default; |
| |
| // Sets a flag indicating that shutdown has started. Returns true if there are |
| // tasks blocking shutdown. Can only be called once. |
| bool StartShutdown() { |
| const auto new_value = |
| subtle::NoBarrier_AtomicIncrement(&bits_, kShutdownHasStartedMask); |
| |
| // Check that the "shutdown has started" bit isn't zero. This would happen |
| // if it was incremented twice. |
| DCHECK(new_value & kShutdownHasStartedMask); |
| |
| const auto num_tasks_blocking_shutdown = |
| new_value >> kNumTasksBlockingShutdownBitOffset; |
| return num_tasks_blocking_shutdown != 0; |
| } |
| |
| // Returns true if shutdown has started. |
| bool HasShutdownStarted() const { |
| return subtle::NoBarrier_Load(&bits_) & kShutdownHasStartedMask; |
| } |
| |
| // Returns true if there are tasks blocking shutdown. |
| bool AreTasksBlockingShutdown() const { |
| const auto num_tasks_blocking_shutdown = |
| subtle::NoBarrier_Load(&bits_) >> kNumTasksBlockingShutdownBitOffset; |
| DCHECK_GE(num_tasks_blocking_shutdown, 0); |
| return num_tasks_blocking_shutdown != 0; |
| } |
| |
| // Increments the number of tasks blocking shutdown. Returns true if shutdown |
| // has started. |
| bool IncrementNumTasksBlockingShutdown() { |
| #if DCHECK_IS_ON() |
| // Verify that no overflow will occur. |
| const auto num_tasks_blocking_shutdown = |
| subtle::NoBarrier_Load(&bits_) >> kNumTasksBlockingShutdownBitOffset; |
| DCHECK_LT(num_tasks_blocking_shutdown, |
| std::numeric_limits<subtle::Atomic32>::max() - |
| kNumTasksBlockingShutdownIncrement); |
| #endif |
| |
| const auto new_bits = subtle::NoBarrier_AtomicIncrement( |
| &bits_, kNumTasksBlockingShutdownIncrement); |
| return new_bits & kShutdownHasStartedMask; |
| } |
| |
| // Decrements the number of tasks blocking shutdown. Returns true if shutdown |
| // has started and the number of tasks blocking shutdown becomes zero. |
| bool DecrementNumTasksBlockingShutdown() { |
| const auto new_bits = subtle::NoBarrier_AtomicIncrement( |
| &bits_, -kNumTasksBlockingShutdownIncrement); |
| const bool shutdown_has_started = new_bits & kShutdownHasStartedMask; |
| const auto num_tasks_blocking_shutdown = |
| new_bits >> kNumTasksBlockingShutdownBitOffset; |
| DCHECK_GE(num_tasks_blocking_shutdown, 0); |
| return shutdown_has_started && num_tasks_blocking_shutdown == 0; |
| } |
| |
| private: |
| static constexpr subtle::Atomic32 kShutdownHasStartedMask = 1; |
| static constexpr subtle::Atomic32 kNumTasksBlockingShutdownBitOffset = 1; |
| static constexpr subtle::Atomic32 kNumTasksBlockingShutdownIncrement = |
| 1 << kNumTasksBlockingShutdownBitOffset; |
| |
| // The LSB indicates whether shutdown has started. The other bits count the |
| // number of tasks blocking shutdown. |
| // No barriers are required to read/write |bits_| as this class is only used |
| // as an atomic state checker, it doesn't provide sequential consistency |
| // guarantees w.r.t. external state. Sequencing of the TaskTracker::State |
| // operations themselves is guaranteed by the AtomicIncrement RMW (read- |
| // modify-write) semantics however. For example, if two threads are racing to |
| // call IncrementNumTasksBlockingShutdown() and StartShutdown() respectively, |
| // either the first thread will win and the StartShutdown() call will see the |
| // blocking task or the second thread will win and |
| // IncrementNumTasksBlockingShutdown() will know that shutdown has started. |
| subtle::Atomic32 bits_ = 0; |
| |
| DISALLOW_COPY_AND_ASSIGN(State); |
| }; |
| |
| struct TaskTracker::PreemptedBackgroundSequence { |
| PreemptedBackgroundSequence() = default; |
| PreemptedBackgroundSequence(scoped_refptr<Sequence> sequence_in, |
| TimeTicks next_task_sequenced_time_in, |
| CanScheduleSequenceObserver* observer_in) |
| : sequence(std::move(sequence_in)), |
| next_task_sequenced_time(next_task_sequenced_time_in), |
| observer(observer_in) {} |
| PreemptedBackgroundSequence(PreemptedBackgroundSequence&& other) = default; |
| ~PreemptedBackgroundSequence() = default; |
| PreemptedBackgroundSequence& operator=(PreemptedBackgroundSequence&& other) = |
| default; |
| bool operator<(const PreemptedBackgroundSequence& other) const { |
| return next_task_sequenced_time < other.next_task_sequenced_time; |
| } |
| bool operator>(const PreemptedBackgroundSequence& other) const { |
| return next_task_sequenced_time > other.next_task_sequenced_time; |
| } |
| |
| // A background sequence waiting to be scheduled. |
| scoped_refptr<Sequence> sequence; |
| |
| // The sequenced time of the next task in |sequence|. |
| TimeTicks next_task_sequenced_time; |
| |
| // An observer to notify when |sequence| can be scheduled. |
| CanScheduleSequenceObserver* observer = nullptr; |
| |
| private: |
| DISALLOW_COPY_AND_ASSIGN(PreemptedBackgroundSequence); |
| }; |
| |
| TaskTracker::TaskTracker(StringPiece histogram_label) |
| : TaskTracker(histogram_label, GetMaxNumScheduledBackgroundSequences()) {} |
| |
| TaskTracker::TaskTracker(StringPiece histogram_label, |
| int max_num_scheduled_background_sequences) |
| : state_(new State), |
| flush_cv_(flush_lock_.CreateConditionVariable()), |
| shutdown_lock_(&flush_lock_), |
| max_num_scheduled_background_sequences_( |
| max_num_scheduled_background_sequences), |
| task_latency_histograms_{ |
| {GetLatencyHistogram("TaskLatencyMicroseconds", |
| histogram_label, |
| "BackgroundTaskPriority"), |
| GetLatencyHistogram("TaskLatencyMicroseconds", |
| histogram_label, |
| "BackgroundTaskPriority_MayBlock")}, |
| {GetLatencyHistogram("TaskLatencyMicroseconds", |
| histogram_label, |
| "UserVisibleTaskPriority"), |
| GetLatencyHistogram("TaskLatencyMicroseconds", |
| histogram_label, |
| "UserVisibleTaskPriority_MayBlock")}, |
| {GetLatencyHistogram("TaskLatencyMicroseconds", |
| histogram_label, |
| "UserBlockingTaskPriority"), |
| GetLatencyHistogram("TaskLatencyMicroseconds", |
| histogram_label, |
| "UserBlockingTaskPriority_MayBlock")}}, |
| heartbeat_latency_histograms_{ |
| {GetLatencyHistogram("HeartbeatLatencyMicroseconds", |
| histogram_label, |
| "BackgroundTaskPriority"), |
| GetLatencyHistogram("HeartbeatLatencyMicroseconds", |
| histogram_label, |
| "BackgroundTaskPriority_MayBlock")}, |
| {GetLatencyHistogram("HeartbeatLatencyMicroseconds", |
| histogram_label, |
| "UserVisibleTaskPriority"), |
| GetLatencyHistogram("HeartbeatLatencyMicroseconds", |
| histogram_label, |
| "UserVisibleTaskPriority_MayBlock")}, |
| {GetLatencyHistogram("HeartbeatLatencyMicroseconds", |
| histogram_label, |
| "UserBlockingTaskPriority"), |
| GetLatencyHistogram("HeartbeatLatencyMicroseconds", |
| histogram_label, |
| "UserBlockingTaskPriority_MayBlock")}}, |
| tracked_ref_factory_(this) { |
| // Confirm that all |task_latency_histograms_| have been initialized above. |
| DCHECK(*(&task_latency_histograms_[static_cast<int>(TaskPriority::HIGHEST) + |
| 1][0] - |
| 1)); |
| } |
| |
| TaskTracker::~TaskTracker() = default; |
| |
| void TaskTracker::Shutdown() { |
| PerformShutdown(); |
| DCHECK(IsShutdownComplete()); |
| |
| // Unblock FlushForTesting() and perform the FlushAsyncForTesting callback |
| // when shutdown completes. |
| { |
| AutoSchedulerLock auto_lock(flush_lock_); |
| flush_cv_->Signal(); |
| } |
| CallFlushCallbackForTesting(); |
| } |
| |
| void TaskTracker::FlushForTesting() { |
| AutoSchedulerLock auto_lock(flush_lock_); |
| while (subtle::Acquire_Load(&num_incomplete_undelayed_tasks_) != 0 && |
| !IsShutdownComplete()) { |
| flush_cv_->Wait(); |
| } |
| } |
| |
| void TaskTracker::FlushAsyncForTesting(OnceClosure flush_callback) { |
| DCHECK(flush_callback); |
| { |
| AutoSchedulerLock auto_lock(flush_lock_); |
| DCHECK(!flush_callback_for_testing_) |
| << "Only one FlushAsyncForTesting() may be pending at any time."; |
| flush_callback_for_testing_ = std::move(flush_callback); |
| } |
| |
| if (subtle::Acquire_Load(&num_incomplete_undelayed_tasks_) == 0 || |
| IsShutdownComplete()) { |
| CallFlushCallbackForTesting(); |
| } |
| } |
| |
| bool TaskTracker::WillPostTask(const Task& task) { |
| DCHECK(task.task); |
| |
| if (!BeforePostTask(task.traits.shutdown_behavior())) |
| return false; |
| |
| if (task.delayed_run_time.is_null()) |
| subtle::NoBarrier_AtomicIncrement(&num_incomplete_undelayed_tasks_, 1); |
| |
| { |
| TRACE_EVENT_WITH_FLOW0( |
| kTaskSchedulerFlowTracingCategory, kQueueFunctionName, |
| TRACE_ID_MANGLE(task_annotator_.GetTaskTraceID(task)), |
| TRACE_EVENT_FLAG_FLOW_OUT); |
| } |
| |
| task_annotator_.DidQueueTask(nullptr, task); |
| |
| return true; |
| } |
| |
| scoped_refptr<Sequence> TaskTracker::WillScheduleSequence( |
| scoped_refptr<Sequence> sequence, |
| CanScheduleSequenceObserver* observer) { |
| const SequenceSortKey sort_key = sequence->GetSortKey(); |
| |
| // A foreground sequence can always be scheduled. |
| if (sort_key.priority() != TaskPriority::BACKGROUND) |
| return sequence; |
| |
| // It is convenient not to have to specify an observer when scheduling |
| // foreground sequences in tests. |
| DCHECK(observer); |
| |
| AutoSchedulerLock auto_lock(background_lock_); |
| |
| if (num_scheduled_background_sequences_ < |
| max_num_scheduled_background_sequences_) { |
| ++num_scheduled_background_sequences_; |
| return sequence; |
| } |
| |
| preempted_background_sequences_.emplace( |
| std::move(sequence), sort_key.next_task_sequenced_time(), observer); |
| return nullptr; |
| } |
| |
| scoped_refptr<Sequence> TaskTracker::RunAndPopNextTask( |
| scoped_refptr<Sequence> sequence, |
| CanScheduleSequenceObserver* observer) { |
| DCHECK(sequence); |
| |
| // Run the next task in |sequence|. |
| Optional<Task> task = sequence->TakeTask(); |
| // TODO(fdoray): Support TakeTask() returning null. https://crbug.com/783309 |
| DCHECK(task); |
| |
| const TaskShutdownBehavior shutdown_behavior = |
| task->traits.shutdown_behavior(); |
| const TaskPriority task_priority = task->traits.priority(); |
| const bool can_run_task = BeforeRunTask(shutdown_behavior); |
| const bool is_delayed = !task->delayed_run_time.is_null(); |
| |
| RunOrSkipTask(std::move(task.value()), sequence.get(), can_run_task); |
| if (can_run_task) |
| AfterRunTask(shutdown_behavior); |
| |
| if (!is_delayed) |
| DecrementNumIncompleteUndelayedTasks(); |
| |
| const bool sequence_is_empty_after_pop = sequence->Pop(); |
| |
| // Never reschedule a Sequence emptied by Pop(). The contract is such that |
| // next poster to make it non-empty is responsible to schedule it. |
| if (sequence_is_empty_after_pop) |
| sequence = nullptr; |
| |
| if (task_priority == TaskPriority::BACKGROUND) { |
| // Allow |sequence| to be rescheduled only if its next task is set to run |
| // earlier than the earliest currently preempted sequence |
| return ManageBackgroundSequencesAfterRunningTask(std::move(sequence), |
| observer); |
| } |
| |
| return sequence; |
| } |
| |
| bool TaskTracker::HasShutdownStarted() const { |
| return state_->HasShutdownStarted(); |
| } |
| |
| bool TaskTracker::IsShutdownComplete() const { |
| AutoSchedulerLock auto_lock(shutdown_lock_); |
| return shutdown_event_ && shutdown_event_->IsSignaled(); |
| } |
| |
| void TaskTracker::SetHasShutdownStartedForTesting() { |
| AutoSchedulerLock auto_lock(shutdown_lock_); |
| |
| // Create a dummy |shutdown_event_| to satisfy TaskTracker's expectation of |
| // its existence during shutdown (e.g. in OnBlockingShutdownTasksComplete()). |
| shutdown_event_.reset( |
| new WaitableEvent(WaitableEvent::ResetPolicy::MANUAL, |
| WaitableEvent::InitialState::NOT_SIGNALED)); |
| |
| state_->StartShutdown(); |
| } |
| |
| void TaskTracker::RecordLatencyHistogram( |
| LatencyHistogramType latency_histogram_type, |
| TaskTraits task_traits, |
| TimeTicks posted_time) const { |
| const TimeDelta task_latency = TimeTicks::Now() - posted_time; |
| |
| DCHECK(latency_histogram_type == LatencyHistogramType::TASK_LATENCY || |
| latency_histogram_type == LatencyHistogramType::HEARTBEAT_LATENCY); |
| auto& histograms = |
| latency_histogram_type == LatencyHistogramType::TASK_LATENCY |
| ? task_latency_histograms_ |
| : heartbeat_latency_histograms_; |
| histograms[static_cast<int>(task_traits.priority())] |
| [task_traits.may_block() || task_traits.with_base_sync_primitives() |
| ? 1 |
| : 0] |
| ->AddTimeMicrosecondsGranularity(task_latency); |
| } |
| |
| void TaskTracker::RunOrSkipTask(Task task, |
| Sequence* sequence, |
| bool can_run_task) { |
| RecordLatencyHistogram(LatencyHistogramType::TASK_LATENCY, task.traits, |
| task.sequenced_time); |
| |
| const bool previous_singleton_allowed = |
| ThreadRestrictions::SetSingletonAllowed( |
| task.traits.shutdown_behavior() != |
| TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN); |
| const bool previous_io_allowed = |
| ThreadRestrictions::SetIOAllowed(task.traits.may_block()); |
| const bool previous_wait_allowed = ThreadRestrictions::SetWaitAllowed( |
| task.traits.with_base_sync_primitives()); |
| |
| { |
| const SequenceToken& sequence_token = sequence->token(); |
| DCHECK(sequence_token.IsValid()); |
| ScopedSetSequenceTokenForCurrentThread |
| scoped_set_sequence_token_for_current_thread(sequence_token); |
| ScopedSetTaskPriorityForCurrentThread |
| scoped_set_task_priority_for_current_thread(task.traits.priority()); |
| ScopedSetSequenceLocalStorageMapForCurrentThread |
| scoped_set_sequence_local_storage_map_for_current_thread( |
| sequence->sequence_local_storage()); |
| |
| // Set up TaskRunnerHandle as expected for the scope of the task. |
| std::unique_ptr<SequencedTaskRunnerHandle> sequenced_task_runner_handle; |
| std::unique_ptr<ThreadTaskRunnerHandle> single_thread_task_runner_handle; |
| DCHECK(!task.sequenced_task_runner_ref || |
| !task.single_thread_task_runner_ref); |
| if (task.sequenced_task_runner_ref) { |
| sequenced_task_runner_handle.reset( |
| new SequencedTaskRunnerHandle(task.sequenced_task_runner_ref)); |
| } else if (task.single_thread_task_runner_ref) { |
| single_thread_task_runner_handle.reset( |
| new ThreadTaskRunnerHandle(task.single_thread_task_runner_ref)); |
| } |
| |
| if (can_run_task) { |
| TRACE_TASK_EXECUTION(kRunFunctionName, task); |
| |
| const char* const execution_mode = |
| task.single_thread_task_runner_ref |
| ? kSingleThreadExecutionMode |
| : (task.sequenced_task_runner_ref ? kSequencedExecutionMode |
| : kParallelExecutionMode); |
| // TODO(gab): In a better world this would be tacked on as an extra arg |
| // to the trace event generated above. This is not possible however until |
| // http://crbug.com/652692 is resolved. |
| TRACE_EVENT1("task_scheduler", "TaskTracker::RunTask", "task_info", |
| std::make_unique<TaskTracingInfo>( |
| task.traits, execution_mode, sequence_token)); |
| |
| { |
| // Put this in its own scope so it preceeds rather than overlaps with |
| // RunTask() in the trace view. |
| TRACE_EVENT_WITH_FLOW0( |
| kTaskSchedulerFlowTracingCategory, kQueueFunctionName, |
| TRACE_ID_MANGLE(task_annotator_.GetTaskTraceID(task)), |
| TRACE_EVENT_FLAG_FLOW_IN); |
| } |
| |
| task_annotator_.RunTask(nullptr, &task); |
| } |
| |
| // Make sure the arguments bound to the callback are deleted within the |
| // scope in which the callback runs. |
| task.task = OnceClosure(); |
| } |
| |
| ThreadRestrictions::SetWaitAllowed(previous_wait_allowed); |
| ThreadRestrictions::SetIOAllowed(previous_io_allowed); |
| ThreadRestrictions::SetSingletonAllowed(previous_singleton_allowed); |
| } |
| |
| void TaskTracker::PerformShutdown() { |
| { |
| AutoSchedulerLock auto_lock(shutdown_lock_); |
| |
| // This method can only be called once. |
| DCHECK(!shutdown_event_); |
| DCHECK(!num_block_shutdown_tasks_posted_during_shutdown_); |
| DCHECK(!state_->HasShutdownStarted()); |
| |
| shutdown_event_.reset( |
| new WaitableEvent(WaitableEvent::ResetPolicy::MANUAL, |
| WaitableEvent::InitialState::NOT_SIGNALED)); |
| |
| const bool tasks_are_blocking_shutdown = state_->StartShutdown(); |
| |
| // From now, if a thread causes the number of tasks blocking shutdown to |
| // become zero, it will call OnBlockingShutdownTasksComplete(). |
| |
| if (!tasks_are_blocking_shutdown) { |
| // If another thread posts a BLOCK_SHUTDOWN task at this moment, it will |
| // block until this method releases |shutdown_lock_|. Then, it will fail |
| // DCHECK(!shutdown_event_->IsSignaled()). This is the desired behavior |
| // because posting a BLOCK_SHUTDOWN task when TaskTracker::Shutdown() has |
| // started and no tasks are blocking shutdown isn't allowed. |
| shutdown_event_->Signal(); |
| return; |
| } |
| } |
| |
| // Remove the cap on the maximum number of background sequences that can be |
| // scheduled concurrently. Done after starting shutdown to ensure that non- |
| // BLOCK_SHUTDOWN sequences don't get a chance to run and that BLOCK_SHUTDOWN |
| // sequences run on threads running with a normal priority. |
| SetMaxNumScheduledBackgroundSequences(std::numeric_limits<int>::max()); |
| |
| // It is safe to access |shutdown_event_| without holding |lock_| because the |
| // pointer never changes after being set above. |
| { |
| base::ThreadRestrictions::ScopedAllowWait allow_wait; |
| shutdown_event_->Wait(); |
| } |
| |
| { |
| AutoSchedulerLock auto_lock(shutdown_lock_); |
| |
| // Record TaskScheduler.BlockShutdownTasksPostedDuringShutdown if less than |
| // |kMaxBlockShutdownTasksPostedDuringShutdown| BLOCK_SHUTDOWN tasks were |
| // posted during shutdown. Otherwise, the histogram has already been |
| // recorded in BeforePostTask(). |
| if (num_block_shutdown_tasks_posted_during_shutdown_ < |
| kMaxBlockShutdownTasksPostedDuringShutdown) { |
| RecordNumBlockShutdownTasksPostedDuringShutdown( |
| num_block_shutdown_tasks_posted_during_shutdown_); |
| } |
| } |
| } |
| |
| void TaskTracker::SetMaxNumScheduledBackgroundSequences( |
| int max_num_scheduled_background_sequences) { |
| std::vector<PreemptedBackgroundSequence> sequences_to_schedule; |
| |
| { |
| AutoSchedulerLock auto_lock(background_lock_); |
| max_num_scheduled_background_sequences_ = |
| max_num_scheduled_background_sequences; |
| |
| while (num_scheduled_background_sequences_ < |
| max_num_scheduled_background_sequences && |
| !preempted_background_sequences_.empty()) { |
| sequences_to_schedule.push_back( |
| GetPreemptedBackgroundSequenceToScheduleLockRequired()); |
| } |
| } |
| |
| for (auto& sequence_to_schedule : sequences_to_schedule) |
| SchedulePreemptedBackgroundSequence(std::move(sequence_to_schedule)); |
| } |
| |
| TaskTracker::PreemptedBackgroundSequence |
| TaskTracker::GetPreemptedBackgroundSequenceToScheduleLockRequired() { |
| background_lock_.AssertAcquired(); |
| DCHECK(!preempted_background_sequences_.empty()); |
| |
| ++num_scheduled_background_sequences_; |
| DCHECK_LE(num_scheduled_background_sequences_, |
| max_num_scheduled_background_sequences_); |
| |
| // The const_cast on top is okay since the PreemptedBackgroundSequence is |
| // transactionnaly being popped from |preempted_background_sequences_| right |
| // after and the move doesn't alter the sort order (a requirement for the |
| // Windows STL's consistency debug-checks for std::priority_queue::top()). |
| PreemptedBackgroundSequence popped_sequence = |
| std::move(const_cast<PreemptedBackgroundSequence&>( |
| preempted_background_sequences_.top())); |
| preempted_background_sequences_.pop(); |
| return popped_sequence; |
| } |
| |
| void TaskTracker::SchedulePreemptedBackgroundSequence( |
| PreemptedBackgroundSequence sequence_to_schedule) { |
| DCHECK(sequence_to_schedule.observer); |
| sequence_to_schedule.observer->OnCanScheduleSequence( |
| std::move(sequence_to_schedule.sequence)); |
| } |
| |
| #if DCHECK_IS_ON() |
| bool TaskTracker::IsPostingBlockShutdownTaskAfterShutdownAllowed() { |
| return false; |
| } |
| #endif |
| |
| bool TaskTracker::HasIncompleteUndelayedTasksForTesting() const { |
| return subtle::Acquire_Load(&num_incomplete_undelayed_tasks_) != 0; |
| } |
| |
| bool TaskTracker::BeforePostTask(TaskShutdownBehavior shutdown_behavior) { |
| if (shutdown_behavior == TaskShutdownBehavior::BLOCK_SHUTDOWN) { |
| // BLOCK_SHUTDOWN tasks block shutdown between the moment they are posted |
| // and the moment they complete their execution. |
| const bool shutdown_started = state_->IncrementNumTasksBlockingShutdown(); |
| |
| if (shutdown_started) { |
| AutoSchedulerLock auto_lock(shutdown_lock_); |
| |
| // A BLOCK_SHUTDOWN task posted after shutdown has completed is an |
| // ordering bug. This aims to catch those early. |
| DCHECK(shutdown_event_); |
| if (shutdown_event_->IsSignaled()) { |
| #if DCHECK_IS_ON() |
| // clang-format off |
| // TODO(robliao): http://crbug.com/698140. Since the service thread |
| // doesn't stop processing its own tasks at shutdown, we may still |
| // attempt to post a BLOCK_SHUTDOWN task in response to a |
| // FileDescriptorWatcher. Same is true for FilePathWatcher |
| // (http://crbug.com/728235). Until it's possible for such services to |
| // post to non-BLOCK_SHUTDOWN sequences which are themselves funneled to |
| // the main execution sequence (a future plan for the post_task.h API), |
| // this DCHECK will be flaky and must be disabled. |
| // DCHECK(IsPostingBlockShutdownTaskAfterShutdownAllowed()); |
| // clang-format on |
| #endif |
| state_->DecrementNumTasksBlockingShutdown(); |
| return false; |
| } |
| |
| ++num_block_shutdown_tasks_posted_during_shutdown_; |
| |
| if (num_block_shutdown_tasks_posted_during_shutdown_ == |
| kMaxBlockShutdownTasksPostedDuringShutdown) { |
| // Record the TaskScheduler.BlockShutdownTasksPostedDuringShutdown |
| // histogram as soon as its upper bound is hit. That way, a value will |
| // be recorded even if an infinite number of BLOCK_SHUTDOWN tasks are |
| // posted, preventing shutdown to complete. |
| RecordNumBlockShutdownTasksPostedDuringShutdown( |
| num_block_shutdown_tasks_posted_during_shutdown_); |
| } |
| } |
| |
| return true; |
| } |
| |
| // A non BLOCK_SHUTDOWN task is allowed to be posted iff shutdown hasn't |
| // started. |
| return !state_->HasShutdownStarted(); |
| } |
| |
| bool TaskTracker::BeforeRunTask(TaskShutdownBehavior shutdown_behavior) { |
| switch (shutdown_behavior) { |
| case TaskShutdownBehavior::BLOCK_SHUTDOWN: { |
| // The number of tasks blocking shutdown has been incremented when the |
| // task was posted. |
| DCHECK(state_->AreTasksBlockingShutdown()); |
| |
| // Trying to run a BLOCK_SHUTDOWN task after shutdown has completed is |
| // unexpected as it either shouldn't have been posted if shutdown |
| // completed or should be blocking shutdown if it was posted before it |
| // did. |
| DCHECK(!state_->HasShutdownStarted() || !IsShutdownComplete()); |
| |
| return true; |
| } |
| |
| case TaskShutdownBehavior::SKIP_ON_SHUTDOWN: { |
| // SKIP_ON_SHUTDOWN tasks block shutdown while they are running. |
| const bool shutdown_started = state_->IncrementNumTasksBlockingShutdown(); |
| |
| if (shutdown_started) { |
| // The SKIP_ON_SHUTDOWN task isn't allowed to run during shutdown. |
| // Decrement the number of tasks blocking shutdown that was wrongly |
| // incremented. |
| const bool shutdown_started_and_no_tasks_block_shutdown = |
| state_->DecrementNumTasksBlockingShutdown(); |
| if (shutdown_started_and_no_tasks_block_shutdown) |
| OnBlockingShutdownTasksComplete(); |
| |
| return false; |
| } |
| |
| return true; |
| } |
| |
| case TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN: { |
| return !state_->HasShutdownStarted(); |
| } |
| } |
| |
| NOTREACHED(); |
| return false; |
| } |
| |
| void TaskTracker::AfterRunTask(TaskShutdownBehavior shutdown_behavior) { |
| if (shutdown_behavior == TaskShutdownBehavior::BLOCK_SHUTDOWN || |
| shutdown_behavior == TaskShutdownBehavior::SKIP_ON_SHUTDOWN) { |
| const bool shutdown_started_and_no_tasks_block_shutdown = |
| state_->DecrementNumTasksBlockingShutdown(); |
| if (shutdown_started_and_no_tasks_block_shutdown) |
| OnBlockingShutdownTasksComplete(); |
| } |
| } |
| |
| void TaskTracker::OnBlockingShutdownTasksComplete() { |
| AutoSchedulerLock auto_lock(shutdown_lock_); |
| |
| // This method can only be called after shutdown has started. |
| DCHECK(state_->HasShutdownStarted()); |
| DCHECK(shutdown_event_); |
| |
| shutdown_event_->Signal(); |
| } |
| |
| void TaskTracker::DecrementNumIncompleteUndelayedTasks() { |
| const auto new_num_incomplete_undelayed_tasks = |
| subtle::Barrier_AtomicIncrement(&num_incomplete_undelayed_tasks_, -1); |
| DCHECK_GE(new_num_incomplete_undelayed_tasks, 0); |
| if (new_num_incomplete_undelayed_tasks == 0) { |
| { |
| AutoSchedulerLock auto_lock(flush_lock_); |
| flush_cv_->Signal(); |
| } |
| CallFlushCallbackForTesting(); |
| } |
| } |
| |
| scoped_refptr<Sequence> TaskTracker::ManageBackgroundSequencesAfterRunningTask( |
| scoped_refptr<Sequence> just_ran_sequence, |
| CanScheduleSequenceObserver* observer) { |
| const TimeTicks next_task_sequenced_time = |
| just_ran_sequence |
| ? just_ran_sequence->GetSortKey().next_task_sequenced_time() |
| : TimeTicks(); |
| PreemptedBackgroundSequence sequence_to_schedule; |
| |
| { |
| AutoSchedulerLock auto_lock(background_lock_); |
| |
| DCHECK(preempted_background_sequences_.empty() || |
| num_scheduled_background_sequences_ == |
| max_num_scheduled_background_sequences_); |
| --num_scheduled_background_sequences_; |
| |
| if (just_ran_sequence) { |
| if (preempted_background_sequences_.empty() || |
| preempted_background_sequences_.top().next_task_sequenced_time > |
| next_task_sequenced_time) { |
| ++num_scheduled_background_sequences_; |
| return just_ran_sequence; |
| } |
| |
| preempted_background_sequences_.emplace( |
| std::move(just_ran_sequence), next_task_sequenced_time, observer); |
| } |
| |
| if (!preempted_background_sequences_.empty()) { |
| sequence_to_schedule = |
| GetPreemptedBackgroundSequenceToScheduleLockRequired(); |
| } |
| } |
| |
| // |sequence_to_schedule.sequence| may be null if there was no preempted |
| // background sequence. |
| if (sequence_to_schedule.sequence) |
| SchedulePreemptedBackgroundSequence(std::move(sequence_to_schedule)); |
| |
| return nullptr; |
| } |
| |
| void TaskTracker::CallFlushCallbackForTesting() { |
| OnceClosure flush_callback; |
| { |
| AutoSchedulerLock auto_lock(flush_lock_); |
| flush_callback = std::move(flush_callback_for_testing_); |
| } |
| if (flush_callback) |
| std::move(flush_callback).Run(); |
| } |
| |
| } // namespace internal |
| } // namespace base |
