blob: c94eef0d4acdaddfe59d307b1fc9cac3b6a0e4dc (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
|
// Copyright 2020 the V8 project 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 INCLUDE_CPPGC_LIVENESS_BROKER_H_
#define INCLUDE_CPPGC_LIVENESS_BROKER_H_
#include "cppgc/heap.h"
#include "cppgc/member.h"
#include "cppgc/trace-trait.h"
#include "v8config.h" // NOLINT(build/include_directory)
namespace cppgc {
namespace internal {
class LivenessBrokerFactory;
} // namespace internal
/**
* The broker is passed to weak callbacks to allow (temporarily) querying
* the liveness state of an object. References to non-live objects must be
* cleared when `IsHeapObjectAlive()` returns false.
*
* \code
* class GCedWithCustomWeakCallback final
* : public GarbageCollected<GCedWithCustomWeakCallback> {
* public:
* UntracedMember<Bar> bar;
*
* void CustomWeakCallbackMethod(const LivenessBroker& broker) {
* if (!broker.IsHeapObjectAlive(bar))
* bar = nullptr;
* }
*
* void Trace(cppgc::Visitor* visitor) const {
* visitor->RegisterWeakCallbackMethod<
* GCedWithCustomWeakCallback,
* &GCedWithCustomWeakCallback::CustomWeakCallbackMethod>(this);
* }
* };
* \endcode
*/
class V8_EXPORT LivenessBroker final {
public:
template <typename T>
bool IsHeapObjectAlive(const T* object) const {
// nullptr objects are considered alive to allow weakness to be used from
// stack while running into a conservative GC. Treating nullptr as dead
// would mean that e.g. custom collectins could not be strongified on stack.
return !object ||
IsHeapObjectAliveImpl(
TraceTrait<T>::GetTraceDescriptor(object).base_object_payload);
}
template <typename T>
bool IsHeapObjectAlive(const WeakMember<T>& weak_member) const {
return (weak_member != kSentinelPointer) &&
IsHeapObjectAlive<T>(weak_member.Get());
}
template <typename T>
bool IsHeapObjectAlive(const UntracedMember<T>& untraced_member) const {
return (untraced_member != kSentinelPointer) &&
IsHeapObjectAlive<T>(untraced_member.Get());
}
private:
LivenessBroker() = default;
bool IsHeapObjectAliveImpl(const void*) const;
friend class internal::LivenessBrokerFactory;
};
} // namespace cppgc
#endif // INCLUDE_CPPGC_LIVENESS_BROKER_H_
|