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ephemeron-pair.h
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1 // Copyright 2020 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef INCLUDE_CPPGC_EPHEMERON_PAIR_H_
6 #define INCLUDE_CPPGC_EPHEMERON_PAIR_H_
7 
8 #include "cppgc/liveness-broker.h"
9 #include "cppgc/member.h"
10 
11 namespace cppgc {
12 
13 /**
14  * An ephemeron pair is used to conditionally retain an object.
15  * The `value` will be kept alive only if the `key` is alive.
16  */
17 template <typename K, typename V>
18 struct EphemeronPair {
19  EphemeronPair(K* k, V* v) : key(k), value(v) {}
20  WeakMember<K> key;
21  Member<V> value;
22 
23  void ClearValueIfKeyIsDead(const LivenessBroker& broker) {
24  if (!broker.IsHeapObjectAlive(key)) value = nullptr;
25  }
26 };
27 
28 } // namespace cppgc
29 
30 #endif // INCLUDE_CPPGC_EPHEMERON_PAIR_H_