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
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
|
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include "Assertions.h"
#include "Atomic.h"
#include "RefCounted.h"
#include "RefPtr.h"
#include "StdLibExtras.h"
#ifdef KERNEL
# include <Kernel/Arch/x86/CPU.h>
#endif
namespace AK {
template<typename T>
class Weakable;
template<typename T>
class WeakPtr;
class WeakLink : public RefCounted<WeakLink> {
template<typename T>
friend class Weakable;
template<typename T>
friend class WeakPtr;
public:
template<typename T, typename PtrTraits = RefPtrTraits<T>, typename EnableIf<IsBaseOf<RefCountedBase, T>>::Type* = nullptr>
RefPtr<T, PtrTraits> strong_ref() const
{
RefPtr<T, PtrTraits> ref;
{
#ifdef KERNEL
// We don't want to be pre-empted while we are trying to obtain
// a strong reference
Kernel::ScopedCritical critical;
#endif
if (!(m_consumers.fetch_add(1u << 1, AK::MemoryOrder::memory_order_acquire) & 1u)) {
T* ptr = (T*)m_ptr.load(AK::MemoryOrder::memory_order_acquire);
if (ptr && ptr->try_ref())
ref = adopt_ref(*ptr);
}
m_consumers.fetch_sub(1u << 1, AK::MemoryOrder::memory_order_release);
}
return ref;
}
template<typename T>
T* unsafe_ptr() const
{
if (m_consumers.load(AK::MemoryOrder::memory_order_relaxed) & 1u)
return nullptr;
// NOTE: This may return a non-null pointer even if revocation
// has been triggered as there is a possible race! But it's "unsafe"
// anyway because we return a raw pointer without ensuring a
// reference...
return (T*)m_ptr.load(AK::MemoryOrder::memory_order_acquire);
}
bool is_null() const
{
return !unsafe_ptr<void>();
}
void revoke()
{
auto current_consumers = m_consumers.fetch_or(1u, AK::MemoryOrder::memory_order_relaxed);
VERIFY(!(current_consumers & 1u));
// We flagged revokation, now wait until everyone trying to obtain
// a strong reference is done
while (current_consumers > 0) {
#ifdef KERNEL
Kernel::Processor::wait_check();
#else
// TODO: yield?
#endif
current_consumers = m_consumers.load(AK::MemoryOrder::memory_order_acquire) & ~1u;
}
// No one is trying to use it (anymore)
m_ptr.store(nullptr, AK::MemoryOrder::memory_order_release);
}
private:
template<typename T>
explicit WeakLink(T& weakable)
: m_ptr(&weakable)
{
}
mutable Atomic<void*> m_ptr;
mutable Atomic<unsigned> m_consumers; // LSB indicates revokation in progress
};
template<typename T>
class Weakable {
private:
class Link;
public:
template<typename U = T>
WeakPtr<U> make_weak_ptr() const;
protected:
Weakable() = default;
~Weakable()
{
m_being_destroyed.store(true, AK::MemoryOrder::memory_order_release);
revoke_weak_ptrs();
}
void revoke_weak_ptrs()
{
if (auto link = move(m_link))
link->revoke();
}
private:
mutable RefPtr<WeakLink> m_link;
Atomic<bool> m_being_destroyed { false };
};
}
using AK::Weakable;
|
