Limit the number of WebGL contexts that are active at any given time

Source/core/html/canvas/WebGLRenderingContext.cpp

Index: Source/core/html/canvas/WebGLRenderingContext.cpp
diff --git a/Source/core/html/canvas/WebGLRenderingContext.cpp b/Source/core/html/canvas/WebGLRenderingContext.cpp
index 5e4be277e3e9c4314adec09b8adda4a6bb2d565d..c66863859b0fbca9042eaa238c238e15668d012a 100644
--- a/Source/core/html/canvas/WebGLRenderingContext.cpp
+++ b/Source/core/html/canvas/WebGLRenderingContext.cpp
@@ -84,6 +84,90 @@ namespace WebCore {
 
 const double secondsBetweenRestoreAttempts = 1.0;
 const int maxGLErrorsAllowedToConsole = 256;
+const int maxGLActiveContexts = 20;
+
+Vector<WebGLRenderingContext*>& WebGLRenderingContext::activeContexts()
+{
+    DEFINE_STATIC_LOCAL(Vector<WebGLRenderingContext*>, activeContexts, ());
+    return activeContexts;
+}
+
+Vector<WebGLRenderingContext*>& WebGLRenderingContext::forciblyEvictedContexts()
+{
+    DEFINE_STATIC_LOCAL(Vector<WebGLRenderingContext*>, forciblyEvictedContexts, ());
+    return forciblyEvictedContexts;
+}
+
+void WebGLRenderingContext::forciblyLoseOldestContext()
+{
+    if (activeContexts().size()) {
+        WebGLRenderingContext* oldestActiveContext = activeContexts().first();
+        activeContexts().remove(0);
+
+        // This will call deactivateContext once the context has actually been lost
+        oldestActiveContext->forceLostContext(WebGLRenderingContext::SyntheticLostContext);
+    }
+}
+
+IntSize WebGLRenderingContext::oldestContextSize()
+{
+    IntSize size;
+
+    if (activeContexts().size()) {
+        WebGLRenderingContext* oldestActiveContext = activeContexts().first();
+        size.setWidth(oldestActiveContext->drawingBufferWidth());
+        size.setHeight(oldestActiveContext->drawingBufferHeight());
+    }
+
+    return size;
+}
+
+void WebGLRenderingContext::activateContext(WebGLRenderingContext* context)
+{
+    if (!activeContexts().contains(context))
+        activeContexts().append(context);
+
+    if (activeContexts().size() > maxGLActiveContexts)
+        forciblyLoseOldestContext();
+}
+
+void WebGLRenderingContext::deactivateContext(WebGLRenderingContext* context, bool addToEvictedList)
+{
+    size_t position = activeContexts().find(context);
+    if (position != WTF::notFound)
+        activeContexts().remove(position);
+
+    if (addToEvictedList && !forciblyEvictedContexts().contains(context))
+        forciblyEvictedContexts().append(context);
+}
+
+void WebGLRenderingContext::willDestroyContext(WebGLRenderingContext* context)
+{
+    size_t position = forciblyEvictedContexts().find(context);
+    if (position != WTF::notFound)
+        forciblyEvictedContexts().remove(position);
+
+    deactivateContext(context, false);
+
+    // Try to re-enable the oldest inactive contexts
+    while(activeContexts().size() < maxGLActiveContexts && forciblyEvictedContexts().size()) {
+        WebGLRenderingContext* evictedContext = forciblyEvictedContexts().first();
+        if (!evictedContext->m_restoreAllowed) {
+            forciblyEvictedContexts().remove(0);
+            continue;
+        }
+
+        IntSize desiredSize = evictedContext->m_drawingBuffer->adjustSize(evictedContext->clampedCanvasSize());
+
+        // If there's room in the pixel budget for this context, restore it!
+        if (!desiredSize.isEmpty()) {
+            forciblyEvictedContexts().remove(0);
+            evictedContext->forceRestoreContext();
+            activeContexts().append(evictedContext);
+        }
+        break;
+    }
+}
 
 namespace {
 
@@ -563,6 +647,8 @@ void WebGLRenderingContext::initializeNewContext()
 
     m_context->setContextLostCallback(adoptPtr(new WebGLRenderingContextLostCallback(this)));
     m_context->setErrorMessageCallback(adoptPtr(new WebGLRenderingContextErrorMessageCallback(this)));
+
+    activateContext(this);
 }
 
 void WebGLRenderingContext::setupFlags()
@@ -623,6 +709,8 @@ WebGLRenderingContext::~WebGLRenderingContext()
     detachAndRemoveAllObjects();
     destroyGraphicsContext3D();
     m_contextGroup->removeContext(this);
+
+    willDestroyContext(this);
 }
 
 void WebGLRenderingContext::destroyGraphicsContext3D()
@@ -5755,6 +5843,7 @@ void WebGLRenderingContext::dispatchContextLostEvent(Timer<WebGLRenderingContext
     RefPtr<WebGLContextEvent> event = WebGLContextEvent::create(eventNames().webglcontextlostEvent, false, true, "");
     canvas()->dispatchEvent(event);
     m_restoreAllowed = event->defaultPrevented();
+    deactivateContext(this, m_contextLostMode != RealLostContext && m_restoreAllowed);
     if (m_contextLostMode == RealLostContext && m_restoreAllowed)
         m_restoreTimer.startOneShot(0);
 }