third_party/blink/renderer/platform/scheduler/common/single_thread_idle_task_runner.h

// Copyright 2014 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 THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_COMMON_SINGLE_THREAD_IDLE_TASK_RUNNER_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_COMMON_SINGLE_THREAD_IDLE_TASK_RUNNER_H_

#include <map>

#include "base/bind.h"
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/single_thread_task_runner.h"
#include "base/time/time.h"
#include "base/trace_event/trace_event.h"
#include "third_party/blink/public/platform/web_common.h"

namespace base {
namespace trace_event {
class BlameContext;
}
}  // namespace base

namespace blink {
namespace scheduler {
class IdleHelper;

// A SingleThreadIdleTaskRunner is a task runner for running idle tasks. Idle
// tasks have an unbound argument which is bound to a deadline
// (in base::TimeTicks) when they are run. The idle task is expected to
// complete by this deadline.
//
// This class uses base::RefCountedThreadSafe instead of WTF::ThreadSafe-
// RefCounted, which is against the general rule for code in platform/
// (see audit_non_blink_usage.py). This is because SingleThreadIdleTaskRunner
// is held by MainThreadSchedulerImpl and MainThreadSchedulerImpl is created
// before WTF (and PartitionAlloc) is initialized.
// TODO(yutak): Fix this.
class SingleThreadIdleTaskRunner
    : public base::RefCountedThreadSafe<SingleThreadIdleTaskRunner> {
 public:
  using IdleTask = base::OnceCallback<void(base::TimeTicks)>;

  // Used to request idle task deadlines and signal posting of idle tasks.
  class BLINK_PLATFORM_EXPORT Delegate {
   public:
    Delegate();
    virtual ~Delegate();

    // Signals that an idle task has been posted. This will be called on the
    // posting thread, which may not be the same thread as the
    // SingleThreadIdleTaskRunner runs on.
    virtual void OnIdleTaskPosted() = 0;

    // Signals that a new idle task is about to be run and returns the deadline
    // for this idle task.
    virtual base::TimeTicks WillProcessIdleTask() = 0;

    // Signals that an idle task has finished being run.
    virtual void DidProcessIdleTask() = 0;

    // Returns the current time.
    virtual base::TimeTicks NowTicks() = 0;

   private:
    DISALLOW_COPY_AND_ASSIGN(Delegate);
  };

  // NOTE Category strings must have application lifetime (statics or
  // literals). They may not include " chars.
  SingleThreadIdleTaskRunner(
      scoped_refptr<base::SingleThreadTaskRunner> idle_priority_task_runner,
      Delegate* delegate);

  virtual void PostIdleTask(const base::Location& from_here,
                            IdleTask idle_task);

  // |idle_task| is eligible to run after the next time an idle period starts
  // after |delay|.  Note this has after wake-up semantics, i.e. unless
  // something else wakes the CPU up, this won't run.
  virtual void PostDelayedIdleTask(const base::Location& from_here,
                                   const base::TimeDelta delay,
                                   IdleTask idle_task);

  virtual void PostNonNestableIdleTask(const base::Location& from_here,
                                       IdleTask idle_task);

  bool RunsTasksInCurrentSequence() const;

  void SetBlameContext(base::trace_event::BlameContext* blame_context);

 protected:
  virtual ~SingleThreadIdleTaskRunner();

 private:
  friend class base::RefCountedThreadSafe<SingleThreadIdleTaskRunner>;
  friend class IdleHelper;

  void RunTask(IdleTask idle_task);

  void EnqueueReadyDelayedIdleTasks();

  using DelayedIdleTask = std::pair<const base::Location, base::OnceClosure>;

  scoped_refptr<base::SingleThreadTaskRunner> idle_priority_task_runner_;
  std::multimap<base::TimeTicks, DelayedIdleTask> delayed_idle_tasks_;
  Delegate* delegate_;                              // NOT OWNED
  base::trace_event::BlameContext* blame_context_;  // Not owned.
  base::WeakPtr<SingleThreadIdleTaskRunner> weak_scheduler_ptr_;
  base::WeakPtrFactory<SingleThreadIdleTaskRunner> weak_factory_;
  DISALLOW_COPY_AND_ASSIGN(SingleThreadIdleTaskRunner);
};

}  // namespace scheduler
}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_COMMON_SINGLE_THREAD_IDLE_TASK_RUNNER_H_