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// 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/base_export.h"
#include "base/callback_forward.h"
#include "base/macros.h"
#include "base/metrics/histogram_base.h"
#include "base/synchronization/condition_variable.h"
#include "base/task_scheduler/scheduler_lock.h"
#include "base/task_scheduler/task.h"
#include "base/task_scheduler/task_traits.h"
namespace base {
namespace internal {
// All tasks go through the scheduler's TaskTracker when they are posted and
// when they are executed. The TaskTracker enforces shutdown semantics 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();
// 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. WillPostTask()
// must have allowed |task| to be posted.
void RunTask(const Task* task);
// Returns true while shutdown is in progress (i.e. Shutdown() has been called
// but hasn't returned).
bool IsShuttingDownForTesting() const;
bool shutdown_completed() const {
AutoSchedulerLock auto_lock(lock_);
return shutdown_completed_;
}
private:
// 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);
// Synchronizes access to all members.
mutable SchedulerLock lock_;
// Condition variable signaled when |num_tasks_blocking_shutdown_| reaches
// zero while shutdown is in progress. Null if shutdown isn't in progress.
std::unique_ptr<ConditionVariable> shutdown_cv_;
// Number of tasks blocking shutdown.
size_t num_tasks_blocking_shutdown_ = 0;
// Number of BLOCK_SHUTDOWN tasks posted during shutdown.
HistogramBase::Sample num_block_shutdown_tasks_posted_during_shutdown_ = 0;
// True once Shutdown() has returned. No new task can be scheduled after this.
bool shutdown_completed_ = false;
DISALLOW_COPY_AND_ASSIGN(TaskTracker);
};
} // namespace internal
} // namespace base
#endif // BASE_TASK_SCHEDULER_TASK_TRACKER_H_