Support "once" event listener option

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 590 matching lines @@
     double blockedEventThreshold = blockedEventsWarningThreshold(context, event);
     double now = 0.0;
     bool shouldReportBlockedEvent = false;
     if (blockedEventThreshold) {
         now = WTF::monotonicallyIncreasingTime();
         shouldReportBlockedEvent = now - event->platformTimeStamp() > blockedEventThreshold;
     }
     bool firedListener = false;
 
     while (i < size) {
-        RegisteredEventListener& registeredListener = entry[i];
+        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::kCapturingPhase && !registeredListener.capture())
             continue;
         if (event->eventPhase() == Event::kBubblingPhase && registeredListener.capture())
             continue;
 
+        EventListener* listener = registeredListener.listener();
+        // The listener will retained by Member<EventListener> in the registeredListener
+        // in case the listener is removed from the listener vector below.
+        if (registeredListener.once())
+            removeEventListener(event->type(), listener, registeredListener.capture());

[tkent, 2016/08/19 02:21:15]

Is it safe to remove a listener while iterating over |entry|?

[Anton Obzhirov, 2016/08/19 10:41:39]

No, it is not, thanks for pointing out. I need to update as minimum
i and size. Basically I need to do similar to what removeEventListenerInternal
does with the firing iterators.

+
         // If stopImmediatePropagation has been called, we just break out immediately, without
         // handling any more events on this target.
         if (event->immediatePropagationStopped())
             break;
 
         event->setHandlingPassive(registeredListener.passive());
         bool passiveForced = registeredListener.passiveForcedForDocumentTarget();
 
         InspectorInstrumentation::NativeBreakpoint nativeBreakpoint(context, this, event);
 
-        EventListener* listener = registeredListener.listener();
-
         // To match Mozilla, the AT_TARGET phase fires both capturing and bubbling
         // event listeners, even though that violates some versions of the DOM spec.
         listener->handleEvent(context, event);
         firedListener = true;
 
         // If we're about to report this event listener as blocking, make sure it wasn't
         // removed while handling the event.
         if (shouldReportBlockedEvent && i > 0 && entry[i - 1].listener() == listener
             && !entry[i - 1].passive() && !entry[i - 1].blockedEventWarningEmitted() && !event->defaultPrevented()) {
             reportBlockedEvent(context, event, &entry[i - 1], now - event->platformTimeStamp());
@@ skipping 50 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