Remove memory_pressure component.

components/memory_pressure/memory_pressure_monitor.h

-// 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.
-//
-// Declares the MemoryPressureMonitor class. This is responsible for monitoring
-// system-wide memory pressure and dispatching memory pressure signals to
-// MemoryPressureListener. It is also responsible for rate limiting calls to the
-// memory pressure subsytem and gathering statistics for UMA.
-//
-// The class has a few compile time differences depending on if
-// MEMORY_PRESSURE_IS_POLLING is defined. For Windows, ChromeOS and Linux
-// the implementation is polling so MEMORY_PRESSURE_IS_POLLING is defined. For
-// Mac, iOS and Android it is not defined.
-//
-// The difference is that "polling" platforms have no native OS signals
-// indicating memory pressure. These platforms implement
-// DirectMemoryPressureCalculator, which is polled on a schedule to check for
-// memory pressure changes. On non-polling platforms the OS provides a native
-// signal. This signal is observed by the platform-specific implementation of
-// MemoryPressureMonitorImpl.
-//
-// The memory pressure system periodically repeats memory pressure signals while
-// under memory pressure (the interval varying depending on the pressure level).
-// As such, even non-polling platforms require a scheduling mechanism for
-// repeating notifications. Both implementations share this basic scheduling
-// subsystem, and also leverage it to make timely UMA reports.
-
-#ifndef COMPONENTS_MEMORY_PRESSURE_MEMORY_PRESSURE_MONITOR_H_
-#define COMPONENTS_MEMORY_PRESSURE_MEMORY_PRESSURE_MONITOR_H_
-
-#include <map>
-#include <memory>
-
-#include "base/callback.h"
-#include "base/memory/weak_ptr.h"
-#include "base/synchronization/lock.h"
-#include "base/time/time.h"
-#include "components/memory_pressure/memory_pressure_listener.h"
-
-namespace base {
-class TaskRunner;
-class TickClock;
-}  // namespace
-
-namespace memory_pressure {
-
-class MemoryPressureCalculator;
-class MemoryPressureStatsCollector;
-
-#if !defined(MEMORY_PRESSURE_IS_POLLING)
-// For non-polling platform specific implementation details. An instance of
-// this class will be encapsulated in the monitor. It will received an injected
-// callback that routes messages to OnMemoryPressureChanged.
-class MemoryPressureMonitorImpl;
-#endif
-
-// A thread-safe class for directly querying and automatically monitoring
-// memory pressure. When system memory pressure levels change this class is
-// responsible for notifying MemoryPressureListeners, and periodically
-// renotifying them as conditions persist. This class will do its periodic work
-// on the thread on which it was created. However, it is safe to call
-// GetCurrentPressureLevel from any thread.
-//
-// This class doesn't make use of base::RepeatingTimer as it leaves an orphaned
-// scheduled task every time it is canceled. This can occur every time a memory
-// pressure level transition occurs, which has no strict upper bound. Instead
-// a collection of at most "number of memory pressure level" scheduled tasks
-// is used, with these tasks being reused as transition levels are crossed and
-// polling requirements change. See |scheduled_checks_| and
-// "ScheduleTaskIfNeededLocked" for details.
-class MemoryPressureMonitor {
- public:
-  using MemoryPressureLevel = MemoryPressureListener::MemoryPressureLevel;
-
-  // A simple dispatch delegate as a testing seam. Makes unittests much simpler
-  // as they don't need to setup a multithreaded environment.
-  using DispatchCallback = base::Callback<void(MemoryPressureLevel)>;
-
-#if defined(MEMORY_PRESSURE_IS_POLLING)
-  // The minimum time that must pass between successive polls. This enforces an
-  // upper bound on the rate of calls to the contained MemoryPressureCalculator.
-  // 100ms (10Hz) allows a relatively fast respsonse time for rapidly increasing
-  // memory usage, but limits the amount of work done in the calculator and
-  // stats collection.
-  enum : int { kMinimumTimeBetweenSamplesMs = 100 };
-  // On polling platforms this is required to be somewhat short in order to
-  // observe memory pressure changes as they occur.
-  enum : int { kDefaultPollingIntervalMs = 5000 };
-#else
-  // On non-polling platforms this is only required for keeping statistics up to
-  // date so can be quite a long period.
-  enum : int { kDefaultPollingIntervalMs = 60000 };
-#endif
-
-  // Renotification intervals, per pressure level. These are the same on all
-  // platforms. These act as an upper bound on the polling interval when under
-  // the corresponding memory pressure.
-  enum : int { kNotificationIntervalPressureModerateMs = 5000 };
-  enum : int { kNotificationIntervalPressureCriticalMs = 1000 };
-
-#if defined(MEMORY_PRESSURE_IS_POLLING)
-  // Fully configurable constructor for polling platforms.
-  MemoryPressureMonitor(const scoped_refptr<base::TaskRunner>& task_runner,
-                        base::TickClock* tick_clock,
-                        MemoryPressureStatsCollector* stats_collector,
-                        MemoryPressureCalculator* calculator,
-                        const DispatchCallback& dispatch_callback);
-#else
-  // Constructor for non-polling platforms.
-  MemoryPressureMonitor(const scoped_refptr<base::TaskRunner>& task_runner,
-                        base::TickClock* tick_clock,
-                        MemoryPressureStatsCollector* stats_collector,
-                        const DispatchCallback& dispatch_callback,
-                        MemoryPressureLevel initial_pressure_level);
-#endif
-
-  ~MemoryPressureMonitor();
-
-  // Returns the current memory pressure level. On polling platforms this may
-  // result in a forced calculation of the current pressure level (a cheap
-  // operation). Can be called from any thread.
-  MemoryPressureLevel GetCurrentPressureLevel();
-
-  // Schedules a memory pressure check to run soon. This can be called from any
-  // thread.
-  void CheckMemoryPressureSoon();
-
- private:
-  // For unittesting.
-  friend class TestMemoryPressureMonitor;
-
-#if !defined(MEMORY_PRESSURE_IS_POLLING)
-  // Notifications from the OS will be routed here by the contained
-  // MemoryPressureMonitorImpl instance. For statistics and renotification to
-  // work properly this must be notified of all pressure level changes, even
-  // those indicating a return to a state of no pressure.
-  void OnMemoryPressureChanged(MemoryPressureLevel level);
-#endif
-
-  // Starts the memory pressure monitor. To be called in the constructor.
-  void Start();
-
-  // Checks memory pressure and updates stats. This is the entry point for all
-  // scheduled checks. Each scheduled check is assigned a |serial| id
-  // (monotonically increasing) which is used to tie the task to the time at
-  // which it was scheduled via the |scheduled_checks_| map.
-  void CheckPressureAndUpdateStats(int serial);
-  void CheckPressureAndUpdateStatsLocked(int serial);
-
-  // Ensures that a task is scheduled for renotification/recalculation/stats
-  // updating. Uses the |serial| id of the current task to determine the time at
-  // which the next scheduled check should run. Assumes |lock_| is held.
-  void ScheduleTaskIfNeededLocked(int serial);
-
-  // Schedules a task.
-  void ScheduleTaskLocked(base::TimeTicks when);
-
-  // A lock for synchronization.
-  base::Lock lock_;
-
-  // Injected dependencies.
-  // The task runner on which periodic pressure checks and statistics uploading
-  // are run.
-  scoped_refptr<base::TaskRunner> task_runner_;
-  // The tick clock in use. Used under |lock_|.
-  base::TickClock* tick_clock_;
-  // The stats collector in use. Used under |lock_|.
-  MemoryPressureStatsCollector* stats_collector_;
-  // The memory pressure calculator in use. Used under |lock_|.
-  MemoryPressureCalculator* calculator_;
-  // The dispatch callback to use.
-  DispatchCallback dispatch_callback_;
-
-#if !defined(MEMORY_PRESSURE_IS_POLLING)
-  // On non-polling platforms this object is responsible for routing OS
-  // notifications to OnMemoryPressureChanged, and setting the initial pressure
-  // value. The OS specific implementation is responsible for allocating this
-  // object.
-  std::unique_ptr<MemoryPressureMonitorImpl> monitor_impl_;
-#endif
-
-  // Object state.
-  // The pressure level as of the most recent poll or notification. Under
-  // |lock_|.
-  MemoryPressureLevel current_memory_pressure_level_;
-#if defined(MEMORY_PRESSURE_IS_POLLING)
-  // Time of the last pressure check. Under |lock_|. Only needed for polling
-  // implementations.
-  base::TimeTicks last_check_;
-#endif
-  // Time of the last pressure notification. Under |lock_|.
-  base::TimeTicks last_notification_;
-  // A map of scheduled pressure checks/statistics updates and their serial
-  // numbers. Under |lock_|.
-  std::map<int, base::TimeTicks> scheduled_checks_;
-  // The most recently assigned serial number for a pressure check. The number
-  // 0 will never be assigned but will instead be reserved for unscheduled
-  // checks initiated externally. Under |lock_|.
-  int serial_number_;
-
-  // Weak pointer factory to ourself used for posting delayed tasks to
-  // task_runner_.
-  base::WeakPtrFactory<MemoryPressureMonitor> weak_ptr_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
-};
-
-}  // namespace memory_pressure
-
-#endif  // COMPONENTS_MEMORY_PRESSURE_MEMORY_PRESSURE_MONITOR_H_