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/*
* Copyright (C) 2008 Apple Inc. All Rights Reserved.
* Copyright (C) 2013 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
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE COMPUTER, INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* 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.
*
*/
#ifndef LifecycleNotifier_h
#define LifecycleNotifier_h
#include "platform/heap/Handle.h"
#include "wtf/AutoReset.h"
#include "wtf/HashSet.h"
namespace blink {
template <typename T, typename Observer>
class LifecycleNotifier : public virtual GarbageCollectedMixin {
public:
virtual ~LifecycleNotifier();
void addObserver(Observer*);
void removeObserver(Observer*);
// notifyContextDestroyed() should be explicitly dispatched from an
// observed context to detach its observers, and if the observer kind
// requires it, notify each observer by invoking contextDestroyed().
//
// When contextDestroyed() is called, it is supplied the context as
// an argument, but the observer's lifecycleContext() is still valid
// and safe to use while handling the notification.
virtual void notifyContextDestroyed();
DEFINE_INLINE_VIRTUAL_TRACE() { visitor->trace(m_observers); }
bool isIteratingOverObservers() const {
return m_iterationState != NotIterating;
}
protected:
LifecycleNotifier() : m_iterationState(NotIterating) {}
T* context() { return static_cast<T*>(this); }
using ObserverSet = HeapHashSet<WeakMember<Observer>>;
enum IterationState {
AllowingNone = 0,
AllowingAddition = 1,
AllowingRemoval = 2,
NotIterating = AllowingAddition | AllowingRemoval,
AllowPendingRemoval = 4,
};
// Iteration state is recorded while iterating the observer set,
// optionally barring add or remove mutations.
IterationState m_iterationState;
ObserverSet m_observers;
};
template <typename T, typename Observer>
inline LifecycleNotifier<T, Observer>::~LifecycleNotifier() {
// FIXME: Enable the following ASSERT. Also see a FIXME in
// Document::detachLayoutTree().
// ASSERT(!m_observers.size());
}
// Determine if |contextDestroyed(Observer*) is a public method on
// class type |Observer|, or any of the class types it derives from.
template <typename Observer, typename T>
class HasContextDestroyed {
using YesType = char;
using NoType = int;
template <typename V>
static YesType checkHasContextDestroyedMethod(
V* observer,
T* context = nullptr,
typename std::enable_if<
std::is_same<decltype(observer->contextDestroyed(context)),
void>::value>::type* g = nullptr);
template <typename V>
static NoType checkHasContextDestroyedMethod(...);
public:
static_assert(sizeof(Observer), "Observer's class declaration not in scope");
static const bool value =
sizeof(YesType) ==
sizeof(checkHasContextDestroyedMethod<Observer>(nullptr));
};
// If |Observer::contextDestroyed()| is present, invoke it.
template <typename Observer,
typename T,
bool = HasContextDestroyed<Observer, T>::value>
class ContextDestroyedNotifier {
STATIC_ONLY(ContextDestroyedNotifier);
public:
static void call(Observer* observer, T* context) {
observer->contextDestroyed(context);
}
};
template <typename Observer, typename T>
class ContextDestroyedNotifier<Observer, T, false> {
STATIC_ONLY(ContextDestroyedNotifier);
public:
static void call(Observer*, T*) {}
};
template <typename T, typename Observer>
inline void LifecycleNotifier<T, Observer>::notifyContextDestroyed() {
// Observer unregistration is allowed, but effectively a no-op.
AutoReset<IterationState> scope(&m_iterationState, AllowingRemoval);
ObserverSet observers;
m_observers.swap(observers);
for (Observer* observer : observers) {
DCHECK(observer->lifecycleContext() == context());
ContextDestroyedNotifier<Observer, T>::call(observer, context());
observer->clearContext();
}
}
template <typename T, typename Observer>
inline void LifecycleNotifier<T, Observer>::addObserver(Observer* observer) {
RELEASE_ASSERT(m_iterationState & AllowingAddition);
m_observers.add(observer);
}
template <typename T, typename Observer>
inline void LifecycleNotifier<T, Observer>::removeObserver(Observer* observer) {
// If immediate removal isn't currently allowed,
// |observer| is recorded for pending removal.
if (m_iterationState & AllowPendingRemoval) {
m_observers.add(observer);
return;
}
RELEASE_ASSERT(m_iterationState & AllowingRemoval);
m_observers.remove(observer);
}
} // namespace blink
#endif // LifecycleNotifier_h
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