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// Copyright 2020 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_OBSERVER_LIST_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_OBSERVER_LIST_H_
#include "base/auto_reset.h"
#include "third_party/blink/renderer/platform/heap/handle.h"
namespace blink {
// A list of observers. Ensures list is not mutated while iterating. Observers
// are not retained.
template <class ObserverType>
class PLATFORM_EXPORT HeapObserverList {
DISALLOW_NEW();
public:
// Add an observer to this list. An observer should not be added to the same
// list more than once.
void AddObserver(ObserverType* observer) {
CHECK(iteration_state_ & kAllowingAddition);
DCHECK(!HasObserver(observer));
observers_.insert(observer);
}
// Removes the given observer from this list. Does nothing if this observer is
// not in this list.
void RemoveObserver(ObserverType* observer) {
CHECK(iteration_state_ & kAllowingRemoval);
observers_.erase(observer);
}
// Determine whether a particular observer is in the list.
bool HasObserver(ObserverType* observer) const {
DCHECK(!IsIteratingOverObservers());
return observers_.Contains(observer);
}
// Returns true if the list is being iterated over.
bool IsIteratingOverObservers() const {
return iteration_state_ != kNotIterating;
}
// Removes all the observers from this list.
void Clear() {
CHECK(iteration_state_ & kAllowingRemoval);
observers_.clear();
}
// Safely iterate over the registered lifecycle observers.
//
// Adding or removing observers is not allowed during iteration. The callable
// will only be called synchronously inside ForEachObserver().
//
// Sample usage:
// ForEachObserver([](ObserverType* observer) {
// observer->SomeMethod();
// });
template <typename ForEachCallable>
void ForEachObserver(const ForEachCallable& callable) const {
base::AutoReset<IterationState> scope(&iteration_state_, kAllowingNone);
for (ObserverType* observer : observers_) {
callable(observer);
}
}
void Trace(Visitor* visitor) const { visitor->Trace(observers_); }
private:
using ObserverSet = HeapLinkedHashSet<WeakMember<ObserverType>>;
// TODO(keishi): Clean up iteration state once transition from
// LifecycleObserver is complete.
enum IterationState {
kAllowingNone = 0,
kAllowingAddition = 1,
kAllowingRemoval = 1 << 1,
kNotIterating = kAllowingAddition | kAllowingRemoval,
};
// Iteration state is recorded while iterating the observer set,
// optionally barring add or remove mutations.
mutable IterationState iteration_state_ = kNotIterating;
ObserverSet observers_;
};
} // namespace blink
#endif // THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_OBSERVER_LIST_H_
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