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// Copyright 2013 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.
// MemoryPressure provides static APIs for handling memory pressure on
// platforms that have such signals, such as Android and ChromeOS.
// The app will try to discard buffers that aren't deemed essential (individual
// modules will implement their own policy).
#include "base/base_export.h"
#include "base/callback.h"
#include "base/macros.h"
namespace base {
// To start listening, create a new instance, passing a callback to a
// function that takes a MemoryPressureLevel parameter. To stop listening,
// simply delete the listener object. The implementation guarantees
// that the callback will always be called on the thread that created
// the listener.
// Note that even on the same thread, the callback is not guaranteed to be
// called synchronously within the system memory pressure broadcast.
// Please see notes in MemoryPressureLevel enum below: some levels are
// absolutely critical, and if not enough memory is returned to the system,
// it'll potentially kill the app, and then later the app will have to be
// cold-started.
// Example:
// void OnMemoryPressure(MemoryPressureLevel memory_pressure_level) {
// ...
// }
// // Start listening.
// auto listener = std::make_unique<MemoryPressureListener>(
// base::BindRepeating(&OnMemoryPressure));
// ...
// // Stop listening.
// listener.reset();
class BASE_EXPORT MemoryPressureListener {
// A Java counterpart will be generated for this enum.
// GENERATED_JAVA_ENUM_PACKAGE: org.chromium.base
enum MemoryPressureLevel {
// No problems, there is enough memory to use. This event is not sent via
// callback, but the enum is used in other places to find out the current
// state of the system.
// Modules are advised to free buffers that are cheap to re-allocate and not
// immediately needed.
// At this level, modules are advised to free all possible memory. The
// alternative is to be killed by the system, which means all memory will
// have to be re-created, plus the cost of a cold start.
using MemoryPressureCallback = RepeatingCallback<void(MemoryPressureLevel)>;
using SyncMemoryPressureCallback =
explicit MemoryPressureListener(
const MemoryPressureCallback& memory_pressure_callback);
const MemoryPressureCallback& memory_pressure_callback,
const SyncMemoryPressureCallback& sync_memory_pressure_callback);
// Intended for use by the platform specific implementation.
static void NotifyMemoryPressure(MemoryPressureLevel memory_pressure_level);
// These methods should not be used anywhere else but in memory measurement
// code, where they are intended to maintain stable conditions across
// measurements.
static bool AreNotificationsSuppressed();
static void SetNotificationsSuppressed(bool suppressed);
static void SimulatePressureNotification(
MemoryPressureLevel memory_pressure_level);
void Notify(MemoryPressureLevel memory_pressure_level);
void SyncNotify(MemoryPressureLevel memory_pressure_level);
static void DoNotifyMemoryPressure(MemoryPressureLevel memory_pressure_level);
MemoryPressureCallback callback_;
SyncMemoryPressureCallback sync_memory_pressure_callback_;
} // namespace base