gfx/layers/MemoryPressureObserver.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "MemoryPressureObserver.h"
   8
   9 #include "mozilla/Services.h"
  10 #include "nsCOMPtr.h"
  11 #include "nsDependentString.h"
  12 #include "nsIObserverService.h"
  13 #include "nsLiteralString.h"
  14
  15 namespace mozilla {
  16 namespace layers {
  17
  18 MemoryPressureObserver::MemoryPressureObserver(
  19     MemoryPressureListener* aListener)
  20     : mListener(aListener) {}
  21
  22 MemoryPressureObserver::~MemoryPressureObserver() {
  23   // If this assertion is hit we probably forgot to unregister the observer.
  24   MOZ_ASSERT(!mListener);
  25 }
  26
  27 already_AddRefed<MemoryPressureObserver> MemoryPressureObserver::Create(
  28     MemoryPressureListener* aListener) {
  29   nsCOMPtr<nsIObserverService> service = services::GetObserverService();
  30
  31   if (!service) {
  32     return nullptr;
  33   }
  34
  35   RefPtr<MemoryPressureObserver> observer =
  36       new MemoryPressureObserver(aListener);
  37
  38   bool useWeakRef = false;
  39   service->AddObserver(observer, "memory-pressure", useWeakRef);
  40
  41   return observer.forget();
  42 }
  43
  44 void MemoryPressureObserver::Unregister() {
  45   if (!mListener) {
  46     return;
  47   }
  48
  49   nsCOMPtr<nsIObserverService> service = services::GetObserverService();
  50   if (service) {
  51     service->RemoveObserver(this, "memory-pressure");
  52   }
  53
  54   mListener = nullptr;
  55 }
  56
  57 NS_IMETHODIMP
  58 MemoryPressureObserver::Observe(nsISupports* aSubject, const char* aTopic,
  59                                 const char16_t* aData) {
  60   if (mListener && strcmp(aTopic, "memory-pressure") == 0) {
  61     MemoryPressureReason reason = MemoryPressureReason::LOW_MEMORY;
  62     auto reason_string = nsDependentString(aData);
  63     if (StringBeginsWith(reason_string, u"low-memory-ongoing"_ns)) {
  64       reason = MemoryPressureReason::LOW_MEMORY_ONGOING;
  65     } else if (StringBeginsWith(reason_string, u"heap-minimize"_ns)) {
  66       reason = MemoryPressureReason::HEAP_MINIMIZE;
  67     }
  68     mListener->OnMemoryPressure(reason);
  69   }
  70
  71   return NS_OK;
  72 }
  73
  74 NS_IMPL_ISUPPORTS(MemoryPressureObserver, nsIObserver)
  75
  76 }  // namespace layers
  77 }  // namespace mozilla