Bug 1154231 - Part 1. Reclaim cached resources when memory-pressure occurs. r=mattwoodrow

widget/PuppetWidget.cpp

@@ -118,6 +118,11 @@ PuppetWidget::Create(nsIWidget        *aParent,
   else {
     Resize(mBounds.x, mBounds.y, mBounds.width, mBounds.height, false);
   }
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    mMemoryPressureObserver = new MemoryPressureObserver(this);
+    obs->AddObserver(mMemoryPressureObserver, "memory-pressure", false);
+  }
 
   return NS_OK;
 }
@@ -153,6 +158,9 @@ PuppetWidget::Destroy()
   Base::OnDestroy();
   Base::Destroy();
   mPaintTask.Revoke();
+  if (mMemoryPressureObserver) {
+    mMemoryPressureObserver->Remove();
+  }
   mChild = nullptr;
   if (mLayerManager) {
     mLayerManager->Destroy();
@@ -175,10 +183,6 @@ PuppetWidget::Show(bool aState)
     mChild->mVisible = aState;
   }
 
-  if (!mVisible && mLayerManager) {
-    mLayerManager->ClearCachedResources();
-  }
-
   if (!wasVisible && mVisible) {
     Resize(mBounds.width, mBounds.height, false);
     Invalidate(mBounds);
@@ -1037,6 +1041,35 @@ PuppetWidget::PaintTask::Run()
   return NS_OK;
 }
 
+NS_IMPL_ISUPPORTS(PuppetWidget::MemoryPressureObserver, nsIObserver)
+
+NS_IMETHODIMP
+PuppetWidget::MemoryPressureObserver::Observe(nsISupports* aSubject,
+                                              const char* aTopic,
+                                              const char16_t* aData)
+{
+  if (!mWidget) {
+    return NS_OK;
+  }
+
+  if (strcmp("memory-pressure", aTopic) == 0) {
+    if (!mWidget->mVisible && mWidget->mLayerManager) {
+      mWidget->mLayerManager->ClearCachedResources();
+    }
+  }
+  return NS_OK;
+}
+
+void
+PuppetWidget::MemoryPressureObserver::Remove()
+{
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->RemoveObserver(this, "memory-pressure");
+  }
+  mWidget = nullptr;
+}
+
 bool
 PuppetWidget::NeedsPaint()
 {

widget/PuppetWidget.h

@@ -279,6 +279,18 @@ private:
     PuppetWidget* mWidget;
   };
 
+  class MemoryPressureObserver : public nsIObserver {
+  public:
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIOBSERVER
+    explicit MemoryPressureObserver(PuppetWidget* aWidget) : mWidget(aWidget) {}
+    void Remove();
+  private:
+    virtual ~MemoryPressureObserver() {}
+    PuppetWidget* mWidget;
+  };
+  friend class MemoryPressureObserver;
+
   // TabChild normally holds a strong reference to this PuppetWidget
   // or its root ancestor, but each PuppetWidget also needs a
   // reference back to TabChild (e.g. to delegate nsIWidget IME calls
@@ -291,6 +303,7 @@ private:
   nsRefPtr<PuppetWidget> mChild;
   nsIntRegion mDirtyRegion;
   nsRevocableEventPtr<PaintTask> mPaintTask;
+  nsRefPtr<MemoryPressureObserver> mMemoryPressureObserver;
   // XXX/cjones: keeping this around until we teach LayerManager to do
   // retained-content-only transactions
   mozilla::RefPtr<DrawTarget> mDrawTarget;