Emit a console warning when blocking event listener is delayed for too long

third_party/WebKit/Source/core/events/EventTarget.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  *           (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ skipping 14 matching lines @@
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  */
 
 #include "core/events/EventTarget.h"
 
 #include "bindings/core/v8/ExceptionState.h"
+#include "bindings/core/v8/ScriptEventListener.h"
 #include "bindings/core/v8/V8DOMActivityLogger.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/editing/Editor.h"
 #include "core/events/Event.h"
+#include "core/frame/FrameHost.h"
+#include "core/frame/LocalDOMWindow.h"
+#include "core/frame/Settings.h"
+#include "core/frame/UseCounter.h"
+#include "core/inspector/ConsoleMessage.h"
 #include "core/inspector/InspectorInstrumentation.h"
-#include "core/frame/LocalDOMWindow.h"
-#include "core/frame/UseCounter.h"
 #include "platform/EventDispatchForbiddenScope.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/Threading.h"
 #include "wtf/Vector.h"
 
 using namespace WTF;
 
 namespace blink {
 namespace {
 
 void setDefaultEventListenerOptionsLegacy(EventListenerOptions& options, bool useCapture)
 {
     options.setCapture(useCapture);
 }
 
 void setDefaultAddEventListenerOptionsLegacy(AddEventListenerOptions& options, bool useCapture)
 {
     setDefaultEventListenerOptionsLegacy(options, useCapture);
     options.setPassive(false);
 }
 
 void setDefaultAddEventListenerOptions(AddEventListenerOptions& options)
 {
     if (!options.hasPassive())
         options.setPassive(false);
 }
 
+double blockedEventsWarningThreshold(const ExecutionContext* context, const Event* event)
+{
+    if (!event->cancelable())
+        return 0.0;
+    const AtomicString& eventType = event->type();
+    if (eventType != EventTypeNames::touchstart
+        && eventType != EventTypeNames::touchmove
+        && eventType != EventTypeNames::touchend
+        && eventType != EventTypeNames::mousewheel
+        && eventType != EventTypeNames::wheel) {
+        return 0.0;
+    }
+
+    if (!context->isDocument())
+        return 0.0;
+    FrameHost* frameHost = toDocument(context)->frameHost();
+    if (!frameHost)
+        return 0.0;
+    return frameHost->settings().blockedMainThreadEventsWarningThreshold();
+}
+
+void reportBlockedEvent(ExecutionContext* context, const Event* event, RegisteredEventListener* registeredListener, double delayedSeconds)
+{
+    if (registeredListener->listener()->type() != EventListener::JSEventListenerType)
+        return;
+
+    V8AbstractEventListener* v8Listener = V8AbstractEventListener::cast(registeredListener->listener());
+    v8::HandleScope handles(v8Listener->isolate());
+    v8::Local<v8::Object> handler = v8Listener->getListenerObject(context);
+
+    String messageText = String::format(
+        "Handling of %s input event was delayed for %ld ms. due to main thread being busy. "

[pfeldman, 2016/05/10 20:01:23]

'%s'

[pfeldman, 2016/05/10 20:01:23]

No need for . after ms

+        "Consider marking event handler as passive to make the page appear more responive.",

[pfeldman, 2016/05/10 20:01:23]

s/appear//

[pfeldman, 2016/05/10 20:01:23]

'passive'

+        event->type().characters8(), lround(delayedSeconds * 1000));
+    ConsoleMessage* message = ConsoleMessage::create(JSMessageSource, WarningMessageLevel, messageText);
+
+    v8::Local<v8::Function> function = eventListenerEffectiveFunction(v8Listener->isolate(), handler);
+    if (!function.IsEmpty()) {
+        message->setLineNumber(function->GetScriptLineNumber() + 1);
+        message->setColumnNumber(function->GetScriptColumnNumber());
+        message->setScriptId(function->ScriptId());
+    }
+    context->addConsoleMessage(message);
+    registeredListener->setBlockedEventWarningEmitted();
+}
+
+
 } // namespace
 
 EventTargetData::EventTargetData()
 {
 }
 
 EventTargetData::~EventTargetData()
 {
 }
 
@@ skipping 340 matching lines @@
         if (LocalDOMWindow* executingWindow = this->executingWindow())
             UseCounter::count(executingWindow->document(), UseCounter::DOMFocusInOutEvent);
     } else if (event->type() == EventTypeNames::focusin || event->type() == EventTypeNames::focusout) {
         if (LocalDOMWindow* executingWindow = this->executingWindow())
             UseCounter::count(executingWindow->document(), UseCounter::FocusInOutEvent);
     } else if (event->type() == EventTypeNames::textInput) {
         if (LocalDOMWindow* executingWindow = this->executingWindow())
             UseCounter::count(executingWindow->document(), UseCounter::TextInputFired);
     }
 
+    ExecutionContext* context = getExecutionContext();
+    if (!context)
+        return;
+
     size_t i = 0;
     size_t size = entry.size();
     if (!d->firingEventIterators)
         d->firingEventIterators = adoptPtr(new FiringEventIteratorVector);
     d->firingEventIterators->append(FiringEventIterator(event->type(), i, size));
+
+    double blockedEventThreshold = blockedEventsWarningThreshold(context, event);
+    double now = 0.0;
+    bool shouldReportBlockedEvent = false;
+    if (blockedEventThreshold) {
+        now = WTF::monotonicallyIncreasingTime();
+        shouldReportBlockedEvent = now - event->platformTimeStamp() > blockedEventThreshold;
+    }
+
     while (i < size) {
         RegisteredEventListener& registeredListener = entry[i];
 
         // Move the iterator past this event listener. This must match
         // the handling of the FiringEventIterator::iterator in
         // EventTarget::removeEventListener.
         ++i;
 
         if (event->eventPhase() == Event::CAPTURING_PHASE && !registeredListener.capture())
             continue;
         if (event->eventPhase() == Event::BUBBLING_PHASE && registeredListener.capture())
             continue;
 
         // If stopImmediatePropagation has been called, we just break out immediately, without
         // handling any more events on this target.
         if (event->immediatePropagationStopped())
             break;
 
-        ExecutionContext* context = getExecutionContext();
-        if (!context)
-            break;
-
         event->setHandlingPassive(registeredListener.passive());
 
         InspectorInstrumentation::NativeBreakpoint nativeBreakpoint(context, this, event);
 
         // To match Mozilla, the AT_TARGET phase fires both capturing and bubbling
         // event listeners, even though that violates some versions of the DOM spec.
         registeredListener.listener()->handleEvent(context, event);
+
+        if (shouldReportBlockedEvent && !registeredListener.passive() && !registeredListener.blockedEventWarningEmitted() && !event->defaultPrevented())
+            reportBlockedEvent(context, event, &registeredListener, now - event->platformTimeStamp());
+
         event->setHandlingPassive(false);
 
         RELEASE_ASSERT(i <= size);
     }
     d->firingEventIterators->removeLast();
 }
 
 DispatchEventResult EventTarget::dispatchEventResult(const Event& event)
 {
     if (event.defaultPrevented())
@@ skipping 28 matching lines @@
     // they have one less listener to invoke.
     if (d->firingEventIterators) {
         for (size_t i = 0; i < d->firingEventIterators->size(); ++i) {
             d->firingEventIterators->at(i).iterator = 0;
             d->firingEventIterators->at(i).end = 0;
         }
     }
 }
 
 } // namespace blink