base/memory/memory_pressure_listener.cc

// 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.

#include "base/memory/memory_pressure_listener.h"

#include "base/lazy_instance.h"
#include "base/observer_list_threadsafe.h"
#include "base/trace_event/trace_event.h"

namespace base {

namespace {

// ObserverListThreadSafe is RefCountedThreadSafe, this traits is needed
// to ensure the LazyInstance will hold a reference to it.
struct LeakyLazyObserverListTraits :
    base::internal::LeakyLazyInstanceTraits<
        ObserverListThreadSafe<MemoryPressureListener> > {
  static ObserverListThreadSafe<MemoryPressureListener>*
      New(void* instance) {
    ObserverListThreadSafe<MemoryPressureListener>* ret =
        base::internal::LeakyLazyInstanceTraits<
            ObserverListThreadSafe<MemoryPressureListener>>::New(instance);
    // Leaky.
    ret->AddRef();
    return ret;
  }
};

LazyInstance<
    ObserverListThreadSafe<MemoryPressureListener>,
    LeakyLazyObserverListTraits> g_observers = LAZY_INSTANCE_INITIALIZER;

// All memory pressure notifications within this process will be suppressed if
// this variable is set to 1.
subtle::Atomic32 g_notifications_suppressed = 0;

}  // namespace

MemoryPressureListener::MemoryPressureListener(
    const MemoryPressureListener::MemoryPressureCallback& callback)
    : callback_(callback) {
  g_observers.Get().AddObserver(this);
}

MemoryPressureListener::~MemoryPressureListener() {
  g_observers.Get().RemoveObserver(this);
}

void MemoryPressureListener::Notify(MemoryPressureLevel memory_pressure_level) {
  callback_.Run(memory_pressure_level);
}

// static
void MemoryPressureListener::NotifyMemoryPressure(
    MemoryPressureLevel memory_pressure_level) {
  DCHECK_NE(memory_pressure_level, MEMORY_PRESSURE_LEVEL_NONE);
  TRACE_EVENT1("memory", "MemoryPressureListener::NotifyMemoryPressure",
      "level", memory_pressure_level);
  if (AreNotificationsSuppressed())
    return;
  DoNotifyMemoryPressure(memory_pressure_level);
}

// static
bool MemoryPressureListener::AreNotificationsSuppressed() {
  return subtle::Acquire_Load(&g_notifications_suppressed) == 1;
}

// static
void MemoryPressureListener::SetNotificationsSuppressed(bool suppress) {
  subtle::Release_Store(&g_notifications_suppressed, suppress ? 1 : 0);
}

// static
void MemoryPressureListener::SimulatePressureNotification(
    MemoryPressureLevel memory_pressure_level) {
  // Notify all listeners even if regular pressure notifications are suppressed.
  DoNotifyMemoryPressure(memory_pressure_level);
}

// static
void MemoryPressureListener::DoNotifyMemoryPressure(
    MemoryPressureLevel memory_pressure_level) {
  DCHECK_NE(memory_pressure_level, MEMORY_PRESSURE_LEVEL_NONE);
  g_observers.Get().Notify(FROM_HERE, &MemoryPressureListener::Notify,
                           memory_pressure_level);
}

}  // namespace base