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// 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.
#include "base/base_export.h"
#include "base/macros.h"
#include "base/memory/memory_pressure_listener.h"
#include "base/memory/memory_pressure_monitor.h"
#include "base/memory/weak_ptr.h"
#include "base/threading/thread_checker.h"
#include "base/timer/timer.h"
// To not pull in windows.h.
namespace base {
namespace win {
// Windows memory pressure monitor. Because there is no OS provided signal this
// polls at a low frequency (once per second), and applies internal hysteresis.
class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
// Constants governing the polling and hysteresis behaviour of the observer.
// The polling interval, in milliseconds. While under critical pressure, this
// is also the timer to repeat cleanup attempts.
static const int kPollingIntervalMs;
// The time which should pass between 2 successive moderate memory pressure
// signals, in milliseconds.
static const int kModeratePressureCooldownMs;
// The number of cycles that should pass between 2 successive moderate memory
// pressure signals.
static const int kModeratePressureCooldownCycles;
// Constants governing the memory pressure level detection.
// The amount of total system memory beyond which a system is considered to be
// a large-memory system.
static const int kLargeMemoryThresholdMb;
// Default minimum free memory thresholds for small-memory systems, in MB.
static const int kSmallMemoryDefaultModerateThresholdMb;
static const int kSmallMemoryDefaultCriticalThresholdMb;
// Default minimum free memory thresholds for large-memory systems, in MB.
static const int kLargeMemoryDefaultModerateThresholdMb;
static const int kLargeMemoryDefaultCriticalThresholdMb;
// Default constructor. Will choose thresholds automatically basd on the
// actual amount of system memory.
// Constructor with explicit memory thresholds. These represent the amount of
// free memory below which the applicable memory pressure state engages.
MemoryPressureMonitor(int moderate_threshold_mb, int critical_threshold_mb);
~MemoryPressureMonitor() override;
// Schedules a memory pressure check to run soon. This must be called on the
// same thread where the monitor was instantiated.
void CheckMemoryPressureSoon();
// Get the current memory pressure level. This can be called from any thread.
MemoryPressureLevel GetCurrentPressureLevel() const override;
// Returns the moderate pressure level free memory threshold, in MB.
int moderate_threshold_mb() const { return moderate_threshold_mb_; }
// Returns the critical pressure level free memory threshold, in MB.
int critical_threshold_mb() const { return critical_threshold_mb_; }
// Internals are exposed for unittests.
// Automatically infers threshold values based on system memory. This invokes
// GetMemoryStatus so it can be mocked in unittests.
void InferThresholds();
// Starts observing the memory fill level. Calls to StartObserving should
// always be matched with calls to StopObserving.
void StartObserving();
// Stop observing the memory fill level. May be safely called if
// StartObserving has not been called. Must be called from the same thread on
// which the monitor was instantiated.
void StopObserving();
// Checks memory pressure, storing the current level, applying any hysteresis
// and emitting memory pressure level change signals as necessary. This
// function is called periodically while the monitor is observing memory
// pressure. This is split out from CheckMemoryPressureAndRecordStatistics so
// that it may be called by CheckMemoryPressureSoon and not invoke UMA
// logging. Must be called from the same thread on which the monitor was
// instantiated.
void CheckMemoryPressure();
// Wrapper to CheckMemoryPressure that also records the observed memory
// pressure level via an UMA enumeration. This is the function that is called
// periodically by the timer. Must be called from the same thread on which the
// monitor was instantiated.
void CheckMemoryPressureAndRecordStatistics();
// Calculates the current instantaneous memory pressure level. This does not
// use any hysteresis and simply returns the result at the current moment. Can
// be called on any thread.
MemoryPressureLevel CalculateCurrentPressureLevel();
// Gets system memory status. This is virtual as a unittesting hook. Returns
// true if the system call succeeds, false otherwise. Can be called on any
// thread.
virtual bool GetSystemMemoryStatus(MEMORYSTATUSEX* mem_status);
// Threshold amounts of available memory that trigger pressure levels. See
// for a discussion of reasonable values for these.
int moderate_threshold_mb_;
int critical_threshold_mb_;
// A periodic timer to check for memory pressure changes.
base::RepeatingTimer timer_;
// The current memory pressure.
MemoryPressureLevel current_memory_pressure_level_;
// To slow down the amount of moderate pressure event calls, this gets used to
// count the number of events since the last event occured. This is used by
// |CheckMemoryPressure| to apply hysteresis on the raw results of
// |CalculateCurrentPressureLevel|.
int moderate_pressure_repeat_count_;
// Ensures that this object is used from a single thread.
base::ThreadChecker thread_checker_;
// Weak pointer factory to ourself used for scheduling calls to
// CheckMemoryPressure/CheckMemoryPressureAndRecordStatistics via |timer_|.
base::WeakPtrFactory<MemoryPressureMonitor> weak_ptr_factory_;
} // namespace win
} // namespace base