| // 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. |
| |
| #ifndef BASE_TASK_SCHEDULER_TASK_TRACKER_H_ |
| #define BASE_TASK_SCHEDULER_TASK_TRACKER_H_ |
| |
| #include <memory> |
| |
| #include "base/atomicops.h" |
| #include "base/base_export.h" |
| #include "base/callback_forward.h" |
| #include "base/macros.h" |
| #include "base/metrics/histogram_base.h" |
| #include "base/synchronization/waitable_event.h" |
| #include "base/task_scheduler/scheduler_lock.h" |
| #include "base/task_scheduler/sequence.h" |
| #include "base/task_scheduler/task.h" |
| #include "base/task_scheduler/task_traits.h" |
| |
| namespace base { |
| |
| class ConditionVariable; |
| class HistogramBase; |
| class SequenceToken; |
| |
| namespace internal { |
| |
| // All tasks go through the scheduler's TaskTracker when they are posted and |
| // when they are executed. The TaskTracker sets up the environment to run tasks, |
| // enforces shutdown semantics, records metrics, and takes care of tracing and |
| // profiling. This class is thread-safe. |
| class BASE_EXPORT TaskTracker { |
| public: |
| TaskTracker(); |
| ~TaskTracker(); |
| |
| // Synchronously shuts down the scheduler. Once this is called, only tasks |
| // posted with the BLOCK_SHUTDOWN behavior will be run. Returns when: |
| // - All SKIP_ON_SHUTDOWN tasks that were already running have completed their |
| // execution. |
| // - All posted BLOCK_SHUTDOWN tasks have completed their execution. |
| // CONTINUE_ON_SHUTDOWN tasks still may be running after Shutdown returns. |
| // This can only be called once. |
| void Shutdown(); |
| |
| // Waits until there are no pending undelayed tasks. May be called in tests |
| // to validate that a condition is met after all undelayed tasks have run. |
| // |
| // Does not wait for delayed tasks. Waits for undelayed tasks posted from |
| // other threads during the call. Returns immediately when shutdown completes. |
| void Flush(); |
| |
| // Informs this TaskTracker that |task| is about to be posted. Returns true if |
| // this operation is allowed (|task| should be posted if-and-only-if it is). |
| bool WillPostTask(const Task* task); |
| |
| // Runs |task| unless the current shutdown state prevents that. |
| // |sequence_token| is the token identifying the sequence from which |task| |
| // was extracted. Returns true if |task| ran. WillPostTask() must have allowed |
| // |task| to be posted before this is called. |
| bool RunTask(std::unique_ptr<Task> task, const SequenceToken& sequence_token); |
| |
| // Returns true once shutdown has started (Shutdown() has been called but |
| // might not have returned). Note: sequential consistency with the thread |
| // calling Shutdown() (or SetHasShutdownStartedForTesting()) isn't guaranteed |
| // by this call. |
| bool HasShutdownStarted() const; |
| |
| // Returns true if shutdown has completed (Shutdown() has returned). |
| bool IsShutdownComplete() const; |
| |
| // Causes HasShutdownStarted() to return true. Unlike when Shutdown() returns, |
| // IsShutdownComplete() won't return true after this returns. Shutdown() |
| // cannot be called after this. |
| void SetHasShutdownStartedForTesting(); |
| |
| protected: |
| // Runs |task|. An override is expected to call its parent's implementation |
| // but is free to perform extra work before and after doing so. |
| virtual void PerformRunTask(std::unique_ptr<Task> task); |
| |
| private: |
| class State; |
| |
| void PerformShutdown(); |
| |
| // Called before WillPostTask() informs the tracing system that a task has |
| // been posted. Updates |num_tasks_blocking_shutdown_| if necessary and |
| // returns true if the current shutdown state allows the task to be posted. |
| bool BeforePostTask(TaskShutdownBehavior shutdown_behavior); |
| |
| // Called before a task with |shutdown_behavior| is run by RunTask(). Updates |
| // |num_tasks_blocking_shutdown_| if necessary and returns true if the current |
| // shutdown state allows the task to be run. |
| bool BeforeRunTask(TaskShutdownBehavior shutdown_behavior); |
| |
| // Called after a task with |shutdown_behavior| has been run by RunTask(). |
| // Updates |num_tasks_blocking_shutdown_| and signals |shutdown_cv_| if |
| // necessary. |
| void AfterRunTask(TaskShutdownBehavior shutdown_behavior); |
| |
| // Called when the number of tasks blocking shutdown becomes zero after |
| // shutdown has started. |
| void OnBlockingShutdownTasksComplete(); |
| |
| // Decrements the number of pending undelayed tasks and signals |flush_cv_| if |
| // it reaches zero. |
| void DecrementNumPendingUndelayedTasks(); |
| |
| // Records the TaskScheduler.TaskLatency.[task priority].[may block] histogram |
| // for |task|. |
| void RecordTaskLatencyHistogram(Task* task); |
| |
| // Number of tasks blocking shutdown and boolean indicating whether shutdown |
| // has started. |
| const std::unique_ptr<State> state_; |
| |
| // Number of undelayed tasks that haven't completed their execution. Is |
| // incremented and decremented without a barrier. When it reaches zero, |
| // |flush_lock_| is acquired (forcing memory synchronization) and |flush_cv_| |
| // is signaled. |
| subtle::Atomic32 num_pending_undelayed_tasks_ = 0; |
| |
| // Lock associated with |flush_cv_|. Partially synchronizes access to |
| // |num_pending_undelayed_tasks_|. Full synchronization isn't needed because |
| // it's atomic, but synchronization is needed to coordinate waking and |
| // sleeping at the right time. |
| mutable SchedulerLock flush_lock_; |
| |
| // Signaled when |num_pending_undelayed_tasks_| is zero or when shutdown |
| // completes. |
| const std::unique_ptr<ConditionVariable> flush_cv_; |
| |
| // Synchronizes access to shutdown related members below. |
| mutable SchedulerLock shutdown_lock_; |
| |
| // Event instantiated when shutdown starts and signaled when shutdown |
| // completes. |
| std::unique_ptr<WaitableEvent> shutdown_event_; |
| |
| // TaskScheduler.TaskLatency.[task priority].[may block] histograms. The first |
| // index is a TaskPriority. The second index is 0 for non-blocking tasks, 1 |
| // for blocking tasks. Intentionally leaked. |
| HistogramBase* const |
| task_latency_histograms_[static_cast<int>(TaskPriority::HIGHEST) + 1][2]; |
| |
| // Number of BLOCK_SHUTDOWN tasks posted during shutdown. |
| HistogramBase::Sample num_block_shutdown_tasks_posted_during_shutdown_ = 0; |
| |
| DISALLOW_COPY_AND_ASSIGN(TaskTracker); |
| }; |
| |
| } // namespace internal |
| } // namespace base |
| |
| #endif // BASE_TASK_SCHEDULER_TASK_TRACKER_H_ |