// Copyright 2015 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_MEMORY_MEMORY_PRESSURE_MONITOR_H_
#define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_H_

#include "base/base_export.h"
#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/memory_pressure_listener.h"
#include "base/time/time.h"

namespace base {

// TODO(chrisha): Make this a concrete class with per-OS implementations rather
// than an abstract base class.

// Declares the interface for a MemoryPressureMonitor. There are multiple
// OS specific implementations of this class. An instance of the memory
// pressure observer is created at the process level, tracks memory usage, and
// pushes memory state change notifications to the static function
// base::MemoryPressureListener::NotifyMemoryPressure. This is turn notifies
// all MemoryPressureListener instances via a callback.
class BASE_EXPORT MemoryPressureMonitor {
 public:
  using MemoryPressureLevel = base::MemoryPressureListener::MemoryPressureLevel;
  using DispatchCallback =
      base::RepeatingCallback<void(MemoryPressureLevel level)>;

  virtual ~MemoryPressureMonitor();

  // Return the singleton MemoryPressureMonitor.
  static MemoryPressureMonitor* Get();

  // Record memory pressure UMA statistic. A tick is 5 seconds.
  static void RecordMemoryPressure(MemoryPressureLevel level, int ticks);

  // Defines the time between UMA events, currently 5s.
  static const base::TimeDelta kUMAMemoryPressureLevelPeriod;

  // Returns the currently observed memory pressure.
  virtual MemoryPressureLevel GetCurrentPressureLevel() const = 0;

  // Sets a notification callback. The default callback invokes
  // base::MemoryPressureListener::NotifyMemoryPressure.
  virtual void SetDispatchCallback(const DispatchCallback& callback) = 0;

 protected:
  MemoryPressureMonitor();

 private:
  DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
};

}  // namespace base

#endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_H_