Free temporary GPU and memory resources held by inactive or hidden 2D canvases

Source/platform/graphics/Canvas2DLayerManager.cpp

 /*
 Copyright (C) 2012 Google Inc. All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 1.  Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
 2.  Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
@@ skipping 13 matching lines @@
 #include "config.h"
 
 #include "platform/graphics/Canvas2DLayerManager.h"
 
 #include "public/platform/Platform.h"
 #include "wtf/StdLibExtras.h"
 
 using blink::WebThread;
 
 namespace {
+
 enum {
     DefaultMaxBytesAllocated = 64*1024*1024,
     DefaultTargetBytesAllocated = 16*1024*1024,
 };
-}
+
+} // unnamed namespace
 
 namespace WebCore {
 
 Canvas2DLayerManager::Canvas2DLayerManager()
     : m_bytesAllocated(0)
     , m_maxBytesAllocated(DefaultMaxBytesAllocated)
     , m_targetBytesAllocated(DefaultTargetBytesAllocated)
     , m_taskObserverActive(false)
 {
 }
@@ skipping 25 matching lines @@
 void Canvas2DLayerManager::willProcessTask()
 {
 }
 
 void Canvas2DLayerManager::didProcessTask()
 {
     // Called after the script action for the current frame has been processed.
     ASSERT(m_taskObserverActive);
     blink::Platform::current()->currentThread()->removeTaskObserver(this);
     m_taskObserverActive = false;
-    for (Canvas2DLayerBridge* layer = m_layerList.head(); layer; layer = layer->next())
-        layer->limitPendingFrames();
+    Canvas2DLayerBridge* layer = m_layerList.head();
+    while (layer) {
+        Canvas2DLayerBridge* currentLayer = layer;
+        layer = layer->next();

[Stephen White, 2014/01/24 18:52:35]

Could you add a comment here explaining why we have to increment layers before
we limit pending frames? Seems a little subtle.

+        currentLayer->limitPendingFrames();
+    }
 }
 
 void Canvas2DLayerManager::layerDidDraw(Canvas2DLayerBridge* layer)
 {
     if (isInList(layer)) {
         if (layer != m_layerList.head()) {
             m_layerList.remove(layer);
             m_layerList.push(layer); // Set as MRU
         }
-    } else
-        addLayerToList(layer);
+    }
 
     if (!m_taskObserverActive) {
         m_taskObserverActive = true;
         // Schedule a call to didProcessTask() after completion of the current script task.
         blink::Platform::current()->currentThread()->addTaskObserver(this);
     }
 }
 
-void Canvas2DLayerManager::addLayerToList(Canvas2DLayerBridge* layer)
+void Canvas2DLayerManager::layerTransientResourceAllocationChanged(Canvas2DLayerBridge* layer, intptr_t deltaBytes)
 {
-    ASSERT(!isInList(layer));
-    m_bytesAllocated += layer->bytesAllocated();
-    m_layerList.push(layer); // Set as MRU
-}
+    ASSERT((intptr_t)m_bytesAllocated + deltaBytes >= 0);
+    m_bytesAllocated = (intptr_t)m_bytesAllocated + deltaBytes;
+    if (!isInList(layer) && layer->hasTransientResources()) {
+        m_layerList.push(layer);
+    } else if (isInList(layer) && !layer->hasTransientResources()) {
+        m_layerList.remove(layer);
+        layer->setNext(0);
+        layer->setPrev(0);
+    }
 
-void Canvas2DLayerManager::layerAllocatedStorageChanged(Canvas2DLayerBridge* layer, intptr_t deltaBytes)
-{
-    if (!isInList(layer))
-        addLayerToList(layer);
-    else {
-        ASSERT((intptr_t)m_bytesAllocated + deltaBytes >= 0);
-        m_bytesAllocated = (intptr_t)m_bytesAllocated + deltaBytes;
-    }
     if (deltaBytes > 0)
         freeMemoryIfNecessary();
 }
 
-void Canvas2DLayerManager::layerToBeDestroyed(Canvas2DLayerBridge* layer)
-{
-    if (isInList(layer))
-        removeLayerFromList(layer);
-}
-
 void Canvas2DLayerManager::freeMemoryIfNecessary()
 {
-    if (m_bytesAllocated > m_maxBytesAllocated) {
+    if (m_bytesAllocated >= m_maxBytesAllocated) {
         // Pass 1: Free memory from caches
         Canvas2DLayerBridge* layer = m_layerList.tail(); // LRU
-        while (m_bytesAllocated > m_targetBytesAllocated && layer) {
-            layer->freeMemoryIfPossible(m_bytesAllocated - m_targetBytesAllocated);
+        while (layer && m_bytesAllocated > m_targetBytesAllocated) {
+            Canvas2DLayerBridge* currentLayer = layer;
             layer = layer->prev();
+            currentLayer->freeMemoryIfPossible(m_bytesAllocated - m_targetBytesAllocated);
+            ASSERT(isInList(currentLayer) == currentLayer->hasTransientResources());
         }
 
         // Pass 2: Flush canvases
-        Canvas2DLayerBridge* leastRecentlyUsedLayer = m_layerList.tail();
-        while (m_bytesAllocated > m_targetBytesAllocated && leastRecentlyUsedLayer) {
-            leastRecentlyUsedLayer->flush();
-            leastRecentlyUsedLayer->freeMemoryIfPossible(~0);
-            removeLayerFromList(leastRecentlyUsedLayer);
-            leastRecentlyUsedLayer = m_layerList.tail();
+        layer = m_layerList.tail();
+        while (m_bytesAllocated > m_targetBytesAllocated && layer) {
+            Canvas2DLayerBridge* currentLayer = layer;
+            layer = layer->prev();
+            currentLayer->flush();
+            currentLayer->freeMemoryIfPossible(m_bytesAllocated - m_targetBytesAllocated);
+            ASSERT(isInList(currentLayer) == currentLayer->hasTransientResources());
         }
     }
 }
 
 void Canvas2DLayerManager::removeLayerFromList(Canvas2DLayerBridge* layer)
 {
     ASSERT(isInList(layer));
-    m_bytesAllocated -= layer->bytesAllocated();
-    m_layerList.remove(layer);
-    layer->setNext(0);
-    layer->setPrev(0);
+    ASSERT(!layer->hasTransientResources());
+
 }
 
-bool Canvas2DLayerManager::isInList(Canvas2DLayerBridge* layer)
+bool Canvas2DLayerManager::isInList(Canvas2DLayerBridge* layer) const
 {
     return layer->prev() || m_layerList.head() == layer;
 }
 
 }