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
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
|
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <cstdint>
#include <memory>
namespace mongo {
template <typename DecoratedType>
class DecorationRegistry;
template <typename DecoratedType>
class Decorable;
/**
* An container for decorations.
*/
template <typename DecoratedType>
class DecorationContainer {
DecorationContainer(const DecorationContainer&) = delete;
DecorationContainer& operator=(const DecorationContainer&) = delete;
public:
/**
* Opaque descriptor of a decoration. It is an identifier to a field on the
* DecorationContainer that is private to those modules that have access to the descriptor.
*/
class DecorationDescriptor {
public:
DecorationDescriptor() = default;
private:
friend DecorationContainer;
friend DecorationRegistry<DecoratedType>;
friend Decorable<DecoratedType>;
explicit DecorationDescriptor(size_t index) : _index(index) {}
size_t _index;
};
/**
* Opaque description of a decoration of specified type T. It is an identifier to a field
* on the DecorationContainer that is private to those modules that have access to the
* descriptor.
*/
template <typename T>
class DecorationDescriptorWithType {
public:
DecorationDescriptorWithType() = default;
private:
friend DecorationContainer;
friend DecorationRegistry<DecoratedType>;
friend Decorable<DecoratedType>;
explicit DecorationDescriptorWithType(DecorationDescriptor raw) : _raw(std::move(raw)) {}
DecorationDescriptor _raw;
};
/**
* Constructs a decorable built based on the given "registry."
*
* The registry must stay in scope for the lifetime of the DecorationContainer, and must not
* have any declareDecoration() calls made on it while a DecorationContainer dependent on it
* is in scope.
*/
explicit DecorationContainer(Decorable<DecoratedType>* const decorated,
const DecorationRegistry<DecoratedType>* const registry)
: _registry(registry),
_decorationData(new unsigned char[registry->getDecorationBufferSizeBytes()]) {
// Because the decorations live in the externally allocated storage buffer at
// `_decorationData`, there needs to be a way to get back from a known location within this
// buffer to the type which owns those decorations. We place a pointer to ourselves, a
// "back link" in the front of this storage buffer, as this is the easiest "well known
// location" to compute.
auto const backLink = reinterpret_cast<Decorable<DecoratedType>**>(_decorationData.get());
*backLink = decorated;
_registry->construct(this);
}
/**
* Constructs a copyable decorable built based on the given "registry."
*
* All decorations are copy constructed from provided DecorationContainer.
*/
explicit DecorationContainer(Decorable<DecoratedType>* const decorated,
const DecorationRegistry<DecoratedType>* const registry,
const DecorationContainer& other)
: _registry(registry),
_decorationData(new unsigned char[registry->getDecorationBufferSizeBytes()]) {
// Because the decorations live in the externally allocated storage buffer at
// `_decorationData`, there needs to be a way to get back from a known location within this
// buffer to the type which owns those decorations. We place a pointer to ourselves, a
// "back link" in the front of this storage buffer, as this is the easiest "well known
// location" to compute.
auto const backLink = reinterpret_cast<Decorable<DecoratedType>**>(_decorationData.get());
*backLink = decorated;
_registry->copyConstruct(this, &other);
}
~DecorationContainer() {
_registry->destroy(this);
}
/**
* Gets the decorated value for the given descriptor.
*
* The descriptor must be one returned from this DecorationContainer's associated _registry.
*/
void* getDecoration(DecorationDescriptor descriptor) {
return _decorationData.get() + descriptor._index;
}
/**
* Same as the non-const form above, but returns a const result.
*/
const void* getDecoration(DecorationDescriptor descriptor) const {
return _decorationData.get() + descriptor._index;
}
/**
* Gets the decorated value or the given typed descriptor.
*/
template <typename T>
T& getDecoration(DecorationDescriptorWithType<T> descriptor) {
return *static_cast<T*>(getDecoration(descriptor._raw));
}
/**
* Same as the non-const form above, but returns a const result.
*/
template <typename T>
const T& getDecoration(DecorationDescriptorWithType<T> descriptor) const {
return *static_cast<const T*>(getDecoration(descriptor._raw));
}
private:
const DecorationRegistry<DecoratedType>* const _registry;
const std::unique_ptr<unsigned char[]> _decorationData;
};
} // namespace mongo
|