xpcom/threads/nsMemoryPressure.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 "nsMemoryPressure.h"
   8 #include "mozilla/Assertions.h"
   9 #include "mozilla/Atomics.h"
  10 #include "mozilla/Services.h"
  11
  12 #include "nsThreadUtils.h"
  13 #include "nsIObserverService.h"
  14
  15 using namespace mozilla;
  16
  17 const char* const kTopicMemoryPressure = "memory-pressure";
  18 const char* const kTopicMemoryPressureStop = "memory-pressure-stop";
  19 const char16_t* const kSubTopicLowMemoryNew = u"low-memory";
  20 const char16_t* const kSubTopicLowMemoryOngoing = u"low-memory-ongoing";
  21
  22 // This is accessed from any thread through NS_NotifyOfEventualMemoryPressure
  23 static Atomic<MemoryPressureState, Relaxed> sMemoryPressurePending(
  24     MemoryPressureState::NoPressure);
  25
  26 void NS_NotifyOfEventualMemoryPressure(MemoryPressureState aState) {
  27   MOZ_ASSERT(aState != MemoryPressureState::None);
  28
  29   /*
  30    * A new memory pressure event erases an ongoing (or stop of) memory pressure,
  31    * but an existing "new" memory pressure event takes precedence over a new
  32    * "ongoing" or "stop" memory pressure event.
  33    */
  34   switch (aState) {
  35     case MemoryPressureState::None:
  36     case MemoryPressureState::LowMemory:
  37       sMemoryPressurePending = aState;
  38       break;
  39     case MemoryPressureState::NoPressure:
  40       sMemoryPressurePending.compareExchange(MemoryPressureState::None, aState);
  41       break;
  42   }
  43 }
  44
  45 nsresult NS_NotifyOfMemoryPressure(MemoryPressureState aState) {
  46   NS_NotifyOfEventualMemoryPressure(aState);
  47   nsCOMPtr<nsIRunnable> event =
  48       new Runnable("NS_DispatchEventualMemoryPressure");
  49   return NS_DispatchToMainThread(event);
  50 }
  51
  52 void NS_DispatchMemoryPressure() {
  53   MOZ_ASSERT(NS_IsMainThread());
  54   static MemoryPressureState sMemoryPressureStatus =
  55       MemoryPressureState::NoPressure;
  56
  57   MemoryPressureState mpPending =
  58       sMemoryPressurePending.exchange(MemoryPressureState::None);
  59   if (mpPending == MemoryPressureState::None) {
  60     return;
  61   }
  62
  63   nsCOMPtr<nsIObserverService> os = services::GetObserverService();
  64   if (!os) {
  65     NS_WARNING("Can't get observer service!");
  66     return;
  67   }
  68
  69   switch (mpPending) {
  70     case MemoryPressureState::None:
  71       MOZ_ASSERT_UNREACHABLE("Already handled this case above.");
  72       break;
  73     case MemoryPressureState::LowMemory:
  74       switch (sMemoryPressureStatus) {
  75         case MemoryPressureState::None:
  76           MOZ_ASSERT_UNREACHABLE("The internal status should never be None.");
  77           break;
  78         case MemoryPressureState::NoPressure:
  79           sMemoryPressureStatus = MemoryPressureState::LowMemory;
  80           os->NotifyObservers(nullptr, kTopicMemoryPressure,
  81                               kSubTopicLowMemoryNew);
  82           break;
  83         case MemoryPressureState::LowMemory:
  84           os->NotifyObservers(nullptr, kTopicMemoryPressure,
  85                               kSubTopicLowMemoryOngoing);
  86           break;
  87       }
  88       break;
  89     case MemoryPressureState::NoPressure:
  90       switch (sMemoryPressureStatus) {
  91         case MemoryPressureState::None:
  92           MOZ_ASSERT_UNREACHABLE("The internal status should never be None.");
  93           break;
  94         case MemoryPressureState::NoPressure:
  95           // Already no pressure.  Do nothing.
  96           break;
  97         case MemoryPressureState::LowMemory:
  98           sMemoryPressureStatus = MemoryPressureState::NoPressure;
  99           os->NotifyObservers(nullptr, kTopicMemoryPressureStop, nullptr);
 100           break;
 101       }
 102       break;
 103   }
 104 }