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comparison clang-tools-extra/clangd/support/Context.h @ 173:0572611fdcc8 llvm10 llvm12

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reorgnization done
author Shinji KONO <kono@ie.u-ryukyu.ac.jp>
date Mon, 25 May 2020 11:55:54 +0900
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172:9fbae9c8bf63 173:0572611fdcc8
1 //===--- Context.h - Mechanism for passing implicit data --------*- C++-*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Context for storing and retrieving implicit data. Useful for passing implicit
10 // parameters on a per-request basis.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_SUPPORT_CONTEXT_H_
15 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_SUPPORT_CONTEXT_H_
16
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/Support/Compiler.h"
19 #include <memory>
20 #include <type_traits>
21
22 namespace clang {
23 namespace clangd {
24
25 /// Values in a Context are indexed by typed keys.
26 /// Key<T> serves two purposes:
27 /// - it provides a lookup key for the context (each Key is unique),
28 /// - it makes lookup type-safe: a Key<T> can only map to a T (or nothing).
29 ///
30 /// Example:
31 /// Key<int> RequestID;
32 /// Key<int> Version;
33 ///
34 /// Context Ctx = Context::empty().derive(RequestID, 10).derive(Version, 3);
35 /// assert(*Ctx.get(RequestID) == 10);
36 /// assert(*Ctx.get(Version) == 3);
37 ///
38 /// Keys are typically used across multiple functions, so most of the time you
39 /// would want to make them static class members or global variables.
40 template <class Type> class Key {
41 public:
42 static_assert(!std::is_reference<Type>::value,
43 "Reference arguments to Key<> are not allowed");
44
45 constexpr Key() = default;
46
47 Key(Key const &) = delete;
48 Key &operator=(Key const &) = delete;
49 Key(Key &&) = delete;
50 Key &operator=(Key &&) = delete;
51 };
52
53 /// A context is an immutable container for per-request data that must be
54 /// propagated through layers that don't care about it. An example is a request
55 /// ID that we may want to use when logging.
56 ///
57 /// Conceptually, a context is a heterogeneous map<Key<T>, T>. Each key has
58 /// an associated value type, which allows the map to be typesafe.
59 ///
60 /// There is an "ambient" context for each thread, Context::current().
61 /// Most functions should read from this, and use WithContextValue or
62 /// WithContext to extend or replace the context within a block scope.
63 /// Only code dealing with threads and extension points should need to use
64 /// other Context objects.
65 ///
66 /// You can't add data to an existing context, instead you create a new
67 /// immutable context derived from it with extra data added. When you retrieve
68 /// data, the context will walk up the parent chain until the key is found.
69 class Context {
70 public:
71 /// Returns an empty root context that contains no data.
72 static Context empty();
73 /// Returns the context for the current thread, creating it if needed.
74 static const Context &current();
75 // Sets the current() context to Replacement, and returns the old context.
76 // Prefer to use WithContext or WithContextValue to do this safely.
77 static Context swapCurrent(Context Replacement);
78
79 private:
80 struct Data;
81 Context(std::shared_ptr<const Data> DataPtr);
82
83 public:
84 /// Same as Context::empty(), please use Context::empty() instead.
85 /// Constructor is defined to workaround a bug in MSVC's version of STL.
86 /// (arguments of std::future<> must be default-constructible in MSVC).
87 Context() = default;
88
89 /// Copy operations for this class are deleted, use an explicit clone() method
90 /// when you need a copy of the context instead.
91 Context(Context const &) = delete;
92 Context &operator=(const Context &) = delete;
93
94 Context(Context &&) = default;
95 Context &operator=(Context &&) = default;
96
97 /// Get data stored for a typed \p Key. If values are not found
98 /// \returns Pointer to the data associated with \p Key. If no data is
99 /// specified for \p Key, return null.
100 template <class Type> const Type *get(const Key<Type> &Key) const {
101 for (const Data *DataPtr = this->DataPtr.get(); DataPtr != nullptr;
102 DataPtr = DataPtr->Parent.get()) {
103 if (DataPtr->KeyPtr == &Key)
104 return static_cast<const Type *>(DataPtr->Value->getValuePtr());
105 }
106 return nullptr;
107 }
108
109 /// A helper to get a reference to a \p Key that must exist in the map.
110 /// Must not be called for keys that are not in the map.
111 template <class Type> const Type &getExisting(const Key<Type> &Key) const {
112 auto Val = get(Key);
113 assert(Val && "Key does not exist");
114 return *Val;
115 }
116
117 /// Derives a child context
118 /// It is safe to move or destroy a parent context after calling derive().
119 /// The child will keep its parent alive, and its data remains accessible.
120 template <class Type>
121 Context derive(const Key<Type> &Key,
122 typename std::decay<Type>::type Value) const & {
123 return Context(std::make_shared<Data>(
124 Data{/*Parent=*/DataPtr, &Key,
125 std::make_unique<TypedAnyStorage<typename std::decay<Type>::type>>(
126 std::move(Value))}));
127 }
128
129 template <class Type>
130 Context
131 derive(const Key<Type> &Key,
132 typename std::decay<Type>::type Value) && /* takes ownership */ {
133 return Context(std::make_shared<Data>(
134 Data{/*Parent=*/std::move(DataPtr), &Key,
135 std::make_unique<TypedAnyStorage<typename std::decay<Type>::type>>(
136 std::move(Value))}));
137 }
138
139 /// Derives a child context, using an anonymous key.
140 /// Intended for objects stored only for their destructor's side-effect.
141 template <class Type> Context derive(Type &&Value) const & {
142 static Key<typename std::decay<Type>::type> Private;
143 return derive(Private, std::forward<Type>(Value));
144 }
145
146 template <class Type> Context derive(Type &&Value) && {
147 static Key<typename std::decay<Type>::type> Private;
148 return std::move(*this).derive(Private, std::forward<Type>(Value));
149 }
150
151 /// Clone this context object.
152 Context clone() const;
153
154 private:
155 class AnyStorage {
156 public:
157 virtual ~AnyStorage() = default;
158 virtual void *getValuePtr() = 0;
159 };
160
161 template <class T> class TypedAnyStorage : public Context::AnyStorage {
162 static_assert(std::is_same<typename std::decay<T>::type, T>::value,
163 "Argument to TypedAnyStorage must be decayed");
164
165 public:
166 TypedAnyStorage(T &&Value) : Value(std::move(Value)) {}
167
168 void *getValuePtr() override { return &Value; }
169
170 private:
171 T Value;
172 };
173
174 struct Data {
175 // We need to make sure Parent outlives the Value, so the order of members
176 // is important. We do that to allow classes stored in Context's child
177 // layers to store references to the data in the parent layers.
178 std::shared_ptr<const Data> Parent;
179 const void *KeyPtr;
180 std::unique_ptr<AnyStorage> Value;
181 };
182
183 std::shared_ptr<const Data> DataPtr;
184 };
185
186 /// WithContext replaces Context::current() with a provided scope.
187 /// When the WithContext is destroyed, the original scope is restored.
188 /// For extending the current context with new value, prefer WithContextValue.
189 class LLVM_NODISCARD WithContext {
190 public:
191 WithContext(Context C) : Restore(Context::swapCurrent(std::move(C))) {}
192 ~WithContext() { Context::swapCurrent(std::move(Restore)); }
193 WithContext(const WithContext &) = delete;
194 WithContext &operator=(const WithContext &) = delete;
195 WithContext(WithContext &&) = delete;
196 WithContext &operator=(WithContext &&) = delete;
197
198 private:
199 Context Restore;
200 };
201
202 /// WithContextValue extends Context::current() with a single value.
203 /// When the WithContextValue is destroyed, the original scope is restored.
204 class LLVM_NODISCARD WithContextValue {
205 public:
206 template <typename T>
207 WithContextValue(const Key<T> &K, typename std::decay<T>::type V)
208 : Restore(Context::current().derive(K, std::move(V))) {}
209
210 // Anonymous values can be used for the destructor side-effect.
211 template <typename T>
212 WithContextValue(T &&V)
213 : Restore(Context::current().derive(std::forward<T>(V))) {}
214
215 private:
216 WithContext Restore;
217 };
218
219 } // namespace clangd
220 } // namespace clang
221
222 #endif