Bug 1062361 - Free cached tiles on memory-pressure r=nical

gfx/layers/client/ClientLayerManager.cpp

@@ -40,6 +40,52 @@ namespace layers {
 
 using namespace mozilla::gfx;
 
+void
+ClientLayerManager::MemoryPressureObserver::Destroy()
+{
+  UnregisterMemoryPressureEvent();
+  mClientLayerManager = nullptr;
+}
+
+NS_IMETHODIMP
+ClientLayerManager::MemoryPressureObserver::Observe(nsISupports* aSubject,
+                                                    const char* aTopic,
+                                                    const char16_t* aSomeData)
+{
+  if (!mClientLayerManager || strcmp(aTopic, "memory-pressure")) {
+    return NS_OK;
+  }
+
+  mClientLayerManager->HandleMemoryPressure();
+  return NS_OK;
+}
+
+void
+ClientLayerManager::MemoryPressureObserver::RegisterMemoryPressureEvent()
+{
+  nsCOMPtr<nsIObserverService> observerService =
+    mozilla::services::GetObserverService();
+
+  MOZ_ASSERT(observerService);
+
+  if (observerService) {
+    observerService->AddObserver(this, "memory-pressure", false);
+  }
+}
+
+void
+ClientLayerManager::MemoryPressureObserver::UnregisterMemoryPressureEvent()
+{
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+
+  if (observerService) {
+      observerService->RemoveObserver(this, "memory-pressure");
+  }
+}
+
+NS_IMPL_ISUPPORTS(ClientLayerManager::MemoryPressureObserver, nsIObserver)
+
 ClientLayerManager::ClientLayerManager(nsIWidget* aWidget)
   : mPhase(PHASE_NONE)
   , mWidget(aWidget)
@@ -54,6 +100,7 @@ ClientLayerManager::ClientLayerManager(nsIWidget* aWidget)
   , mForwarder(new ShadowLayerForwarder)
 {
   MOZ_COUNT_CTOR(ClientLayerManager);
+  mMemoryPressureObserver = new MemoryPressureObserver(this);
 }
 
 ClientLayerManager::~ClientLayerManager()
@@ -61,6 +108,7 @@ ClientLayerManager::~ClientLayerManager()
   if (mTransactionIdAllocator) {
     DidComposite(mLatestTransactionId);
   }
+  mMemoryPressureObserver->Destroy();
   ClearCachedResources();
   // Stop receiveing AsyncParentMessage at Forwarder.
   // After the call, the message is directly handled by LayerTransactionChild. 
@@ -622,6 +670,14 @@ ClientLayerManager::ClearCachedResources(Layer* aSubtree)
   }
 }
 
+void
+ClientLayerManager::HandleMemoryPressure()
+{
+  for (size_t i = 0; i < mTexturePools.Length(); i++) {
+    mTexturePools[i]->ShrinkToMinimumSize();
+  }
+}
+
 void
 ClientLayerManager::ClearLayer(Layer* aLayer)
 {

gfx/layers/client/ClientLayerManager.h

@@ -20,6 +20,7 @@
 #include "nsAutoPtr.h"                  // for nsRefPtr
 #include "nsCOMPtr.h"                   // for already_AddRefed
 #include "nsDebug.h"                    // for NS_ABORT_IF_FALSE
+#include "nsIObserver.h"                // for nsIObserver
 #include "nsISupportsImpl.h"            // for Layer::Release, etc
 #include "nsRect.h"                     // for nsIntRect
 #include "nsTArray.h"                   // for nsTArray
@@ -123,6 +124,8 @@ public:
   // if we have one.
   virtual void ClearCachedResources(Layer* aSubtree = nullptr) MOZ_OVERRIDE;
 
+  void HandleMemoryPressure();
+
   void SetRepeatTransaction() { mRepeatTransaction = true; }
   bool GetRepeatTransaction() { return mRepeatTransaction; }
 
@@ -235,6 +238,29 @@ protected:
   TransactionPhase mPhase;
 
 private:
+  // Listen memory-pressure event for ClientLayerManager
+  class MemoryPressureObserver MOZ_FINAL : public nsIObserver
+  {
+  public:
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIOBSERVER
+
+    MemoryPressureObserver(ClientLayerManager* aClientLayerManager)
+      : mClientLayerManager(aClientLayerManager)
+    {
+      RegisterMemoryPressureEvent();
+    }
+
+    void Destroy();
+
+  private:
+    virtual ~MemoryPressureObserver() {}
+    void RegisterMemoryPressureEvent();
+    void UnregisterMemoryPressureEvent();
+
+    ClientLayerManager* mClientLayerManager;
+  };
+
   /**
    * Forward transaction results to the parent context.
    */
@@ -304,6 +330,8 @@ private:
 
   // indexed by gfx::SurfaceFormat
   nsTArray<RefPtr<SimpleTextureClientPool> > mSimpleTilePools;
+
+  nsRefPtr<MemoryPressureObserver> mMemoryPressureObserver;
 };
 
 class ClientLayer : public ShadowableLayer