1 // Copyright (c) 2018 The Chromium 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.
5 // This header file contains macro definitions for thread safety annotations
6 // that allow developers to document the locking policies of multi-threaded
7 // code. The annotations can also help program analysis tools to identify
8 // potential thread safety issues.
10 // Note that the annotations we use are described as deprecated in the Clang
11 // documentation, linked below. E.g. we use EXCLUSIVE_LOCKS_REQUIRED where the
12 // Clang docs use REQUIRES.
14 // http://clang.llvm.org/docs/ThreadSafetyAnalysis.html
16 // We use the deprecated Clang annotations to match Abseil (relevant header
17 // linked below) and its ecosystem of libraries. We will follow Abseil with
18 // respect to upgrading to more modern annotations.
20 // https://github.com/abseil/abseil-cpp/blob/master/absl/base/thread_annotations.h
22 // These annotations are implemented using compiler attributes. Using the macros
23 // defined here instead of raw attributes allow for portability and future
26 // When referring to mutexes in the arguments of the attributes, you should
27 // use variable names or more complex expressions (e.g. my_object->mutex_)
28 // that evaluate to a concrete mutex object whenever possible. If the mutex
29 // you want to refer to is not in scope, you may use a member pointer
30 // (e.g. &MyClass::mutex_) to refer to a mutex in some (unknown) object.
32 #ifndef THREAD_ANNOTATIONS_H_
33 #define THREAD_ANNOTATIONS_H_
35 #if defined(__clang__)
36 #define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
38 #define THREAD_ANNOTATION_ATTRIBUTE__(x) // no-op
43 // Documents if a shared field or global variable needs to be protected by a
44 // mutex. GUARDED_BY() allows the user to specify a particular mutex that
45 // should be held when accessing the annotated variable.
50 // int p1 GUARDED_BY(mu);
51 #define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
55 // Documents if the memory location pointed to by a pointer should be guarded
56 // by a mutex when dereferencing the pointer.
60 // int *p1 PT_GUARDED_BY(mu);
62 // Note that a pointer variable to a shared memory location could itself be a
67 // // `q`, guarded by `mu1`, points to a shared memory location that is
68 // // guarded by `mu2`:
69 // int *q GUARDED_BY(mu1) PT_GUARDED_BY(mu2);
70 #define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
72 // ACQUIRED_AFTER() / ACQUIRED_BEFORE()
74 // Documents the acquisition order between locks that can be held
75 // simultaneously by a thread. For any two locks that need to be annotated
76 // to establish an acquisition order, only one of them needs the annotation.
77 // (i.e. You don't have to annotate both locks with both ACQUIRED_AFTER
78 // and ACQUIRED_BEFORE.)
83 // Mutex m2 ACQUIRED_AFTER(m1);
84 #define ACQUIRED_AFTER(...) \
85 THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))
87 #define ACQUIRED_BEFORE(...) \
88 THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))
90 // EXCLUSIVE_LOCKS_REQUIRED() / SHARED_LOCKS_REQUIRED()
92 // Documents a function that expects a mutex to be held prior to entry.
93 // The mutex is expected to be held both on entry to, and exit from, the
99 // int a GUARDED_BY(mu1);
100 // int b GUARDED_BY(mu2);
102 // void foo() EXCLUSIVE_LOCKS_REQUIRED(mu1, mu2) { ... };
103 #define EXCLUSIVE_LOCKS_REQUIRED(...) \
104 THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))
106 #define SHARED_LOCKS_REQUIRED(...) \
107 THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))
111 // Documents the locks acquired in the body of the function. These locks
112 // cannot be held when calling this function (as Abseil's `Mutex` locks are
114 #define LOCKS_EXCLUDED(...) \
115 THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
119 // Documents a function that returns a mutex without acquiring it. For example,
120 // a public getter method that returns a pointer to a private mutex should
121 // be annotated with LOCK_RETURNED.
122 #define LOCK_RETURNED(x) THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
126 // Documents if a class/type is a lockable type (such as the `Mutex` class).
127 #define LOCKABLE THREAD_ANNOTATION_ATTRIBUTE__(lockable)
131 // Documents if a class does RAII locking (such as the `MutexLock` class).
132 // The constructor should use `LOCK_FUNCTION()` to specify the mutex that is
133 // acquired, and the destructor should use `UNLOCK_FUNCTION()` with no
134 // arguments; the analysis will assume that the destructor unlocks whatever the
135 // constructor locked.
136 #define SCOPED_LOCKABLE THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
138 // EXCLUSIVE_LOCK_FUNCTION()
140 // Documents functions that acquire a lock in the body of a function, and do
142 #define EXCLUSIVE_LOCK_FUNCTION(...) \
143 THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))
145 // SHARED_LOCK_FUNCTION()
147 // Documents functions that acquire a shared (reader) lock in the body of a
148 // function, and do not release it.
149 #define SHARED_LOCK_FUNCTION(...) \
150 THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))
154 // Documents functions that expect a lock to be held on entry to the function,
155 // and release it in the body of the function.
156 #define UNLOCK_FUNCTION(...) \
157 THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))
159 // EXCLUSIVE_TRYLOCK_FUNCTION() / SHARED_TRYLOCK_FUNCTION()
161 // Documents functions that try to acquire a lock, and return success or failure
162 // (or a non-boolean value that can be interpreted as a boolean).
163 // The first argument should be `true` for functions that return `true` on
164 // success, or `false` for functions that return `false` on success. The second
165 // argument specifies the mutex that is locked on success. If unspecified, this
166 // mutex is assumed to be `this`.
167 #define EXCLUSIVE_TRYLOCK_FUNCTION(...) \
168 THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))
170 #define SHARED_TRYLOCK_FUNCTION(...) \
171 THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))
173 // ASSERT_EXCLUSIVE_LOCK() / ASSERT_SHARED_LOCK()
175 // Documents functions that dynamically check to see if a lock is held, and fail
176 // if it is not held.
177 #define ASSERT_EXCLUSIVE_LOCK(...) \
178 THREAD_ANNOTATION_ATTRIBUTE__(assert_exclusive_lock(__VA_ARGS__))
180 #define ASSERT_SHARED_LOCK(...) \
181 THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_lock(__VA_ARGS__))
183 // NO_THREAD_SAFETY_ANALYSIS
185 // Turns off thread safety checking within the body of a particular function.
186 // This annotation is used to mark functions that are known to be correct, but
187 // the locking behavior is more complicated than the analyzer can handle.
188 #define NO_THREAD_SAFETY_ANALYSIS \
189 THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
191 //------------------------------------------------------------------------------
192 // Tool-Supplied Annotations
193 //------------------------------------------------------------------------------
195 // TS_UNCHECKED should be placed around lock expressions that are not valid
196 // C++ syntax, but which are present for documentation purposes. These
197 // annotations will be ignored by the analysis.
198 #define TS_UNCHECKED(x) ""
200 // TS_FIXME is used to mark lock expressions that are not valid C++ syntax.
201 // It is used by automated tools to mark and disable invalid expressions.
202 // The annotation should either be fixed, or changed to TS_UNCHECKED.
203 #define TS_FIXME(x) ""
205 // Like NO_THREAD_SAFETY_ANALYSIS, this turns off checking within the body of
206 // a particular function. However, this attribute is used to mark functions
207 // that are incorrect and need to be fixed. It is used by automated tools to
208 // avoid breaking the build when the analysis is updated.
209 // Code owners are expected to eventually fix the routine.
210 #define NO_THREAD_SAFETY_ANALYSIS_FIXME NO_THREAD_SAFETY_ANALYSIS
212 // Similar to NO_THREAD_SAFETY_ANALYSIS_FIXME, this macro marks a GUARDED_BY
213 // annotation that needs to be fixed, because it is producing thread safety
214 // warning. It disables the GUARDED_BY.
215 #define GUARDED_BY_FIXME(x)
217 // Disables warnings for a single read operation. This can be used to avoid
218 // warnings when it is known that the read is not actually involved in a race,
219 // but the compiler cannot confirm that.
220 #define TS_UNCHECKED_READ(x) thread_safety_analysis::ts_unchecked_read(x)
222 namespace thread_safety_analysis {
224 // Takes a reference to a guarded data member, and returns an unguarded
226 template <typename T>
227 inline const T& ts_unchecked_read(const T& v) NO_THREAD_SAFETY_ANALYSIS {
231 template <typename T>
232 inline T& ts_unchecked_read(T& v) NO_THREAD_SAFETY_ANALYSIS {
236 } // namespace thread_safety_analysis
238 #endif // _BASE_THREAD_ANNOTATIONS_H_