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 no analysis is done inside constructors and destructors,
11 // regardless of what attributes are used. See
12 // https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#no-checking-inside-constructors-and-destructors
15 // Note that the annotations we use are described as deprecated in the Clang
16 // documentation, linked below. E.g. we use EXCLUSIVE_LOCKS_REQUIRED where the
17 // Clang docs use REQUIRES.
19 // http://clang.llvm.org/docs/ThreadSafetyAnalysis.html
21 // We use the deprecated Clang annotations to match Abseil (relevant header
22 // linked below) and its ecosystem of libraries. We will follow Abseil with
23 // respect to upgrading to more modern annotations.
25 // https://github.com/abseil/abseil-cpp/blob/master/absl/base/thread_annotations.h
27 // These annotations are implemented using compiler attributes. Using the macros
28 // defined here instead of raw attributes allow for portability and future
31 // When referring to mutexes in the arguments of the attributes, you should
32 // use variable names or more complex expressions (e.g. my_object->mutex_)
33 // that evaluate to a concrete mutex object whenever possible. If the mutex
34 // you want to refer to is not in scope, you may use a member pointer
35 // (e.g. &MyClass::mutex_) to refer to a mutex in some (unknown) object.
37 #ifndef BASE_THREAD_ANNOTATIONS_H_
38 #define BASE_THREAD_ANNOTATIONS_H_
40 #include "base/check_op.h"
41 #include "build/build_config.h"
43 #if defined(__clang__)
44 #define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
46 #define THREAD_ANNOTATION_ATTRIBUTE__(x) // no-op
51 // Documents if a shared field or global variable needs to be protected by a
52 // mutex. GUARDED_BY() allows the user to specify a particular mutex that
53 // should be held when accessing the annotated variable.
58 // int p1 GUARDED_BY(mu);
59 #define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
63 // Documents if the memory location pointed to by a pointer should be guarded
64 // by a mutex when dereferencing the pointer.
68 // int *p1 PT_GUARDED_BY(mu);
70 // Note that a pointer variable to a shared memory location could itself be a
75 // // `q`, guarded by `mu1`, points to a shared memory location that is
76 // // guarded by `mu2`:
77 // int *q GUARDED_BY(mu1) PT_GUARDED_BY(mu2);
78 #define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
80 // ACQUIRED_AFTER() / ACQUIRED_BEFORE()
82 // Documents the acquisition order between locks that can be held
83 // simultaneously by a thread. For any two locks that need to be annotated
84 // to establish an acquisition order, only one of them needs the annotation.
85 // (i.e. You don't have to annotate both locks with both ACQUIRED_AFTER
86 // and ACQUIRED_BEFORE.)
91 // Mutex m2 ACQUIRED_AFTER(m1);
92 #define ACQUIRED_AFTER(...) \
93 THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))
95 #define ACQUIRED_BEFORE(...) \
96 THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))
98 // EXCLUSIVE_LOCKS_REQUIRED() / SHARED_LOCKS_REQUIRED()
100 // Documents a function that expects a mutex to be held prior to entry.
101 // The mutex is expected to be held both on entry to, and exit from, the
107 // int a GUARDED_BY(mu1);
108 // int b GUARDED_BY(mu2);
110 // void foo() EXCLUSIVE_LOCKS_REQUIRED(mu1, mu2) { ... };
111 #define EXCLUSIVE_LOCKS_REQUIRED(...) \
112 THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))
114 #define SHARED_LOCKS_REQUIRED(...) \
115 THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))
119 // Documents the locks acquired in the body of the function. These locks
120 // cannot be held when calling this function (as Abseil's `Mutex` locks are
122 #define LOCKS_EXCLUDED(...) \
123 THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
127 // Documents a function that returns a mutex without acquiring it. For example,
128 // a public getter method that returns a pointer to a private mutex should
129 // be annotated with LOCK_RETURNED.
130 #define LOCK_RETURNED(x) THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
134 // Documents if a class/type is a lockable type (such as the `Mutex` class).
135 #define LOCKABLE THREAD_ANNOTATION_ATTRIBUTE__(lockable)
139 // Documents if a class does RAII locking (such as the `MutexLock` class).
140 // The constructor should use `LOCK_FUNCTION()` to specify the mutex that is
141 // acquired, and the destructor should use `UNLOCK_FUNCTION()` with no
142 // arguments; the analysis will assume that the destructor unlocks whatever the
143 // constructor locked.
144 #define SCOPED_LOCKABLE THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
146 // EXCLUSIVE_LOCK_FUNCTION()
148 // Documents functions that acquire a lock in the body of a function, and do
150 #define EXCLUSIVE_LOCK_FUNCTION(...) \
151 THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))
153 // SHARED_LOCK_FUNCTION()
155 // Documents functions that acquire a shared (reader) lock in the body of a
156 // function, and do not release it.
157 #define SHARED_LOCK_FUNCTION(...) \
158 THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))
162 // Documents functions that expect a lock to be held on entry to the function,
163 // and release it in the body of the function.
164 #define UNLOCK_FUNCTION(...) \
165 THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))
167 // EXCLUSIVE_TRYLOCK_FUNCTION() / SHARED_TRYLOCK_FUNCTION()
169 // Documents functions that try to acquire a lock, and return success or failure
170 // (or a non-boolean value that can be interpreted as a boolean).
171 // The first argument should be `true` for functions that return `true` on
172 // success, or `false` for functions that return `false` on success. The second
173 // argument specifies the mutex that is locked on success. If unspecified, this
174 // mutex is assumed to be `this`.
175 #define EXCLUSIVE_TRYLOCK_FUNCTION(...) \
176 THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))
178 #define SHARED_TRYLOCK_FUNCTION(...) \
179 THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))
181 // ASSERT_EXCLUSIVE_LOCK() / ASSERT_SHARED_LOCK()
183 // Documents functions that dynamically check to see if a lock is held, and fail
184 // if it is not held.
185 #define ASSERT_EXCLUSIVE_LOCK(...) \
186 THREAD_ANNOTATION_ATTRIBUTE__(assert_exclusive_lock(__VA_ARGS__))
188 #define ASSERT_SHARED_LOCK(...) \
189 THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_lock(__VA_ARGS__))
191 // NO_THREAD_SAFETY_ANALYSIS
193 // Turns off thread safety checking within the body of a particular function.
194 // This annotation is used to mark functions that are known to be correct, but
195 // the locking behavior is more complicated than the analyzer can handle.
196 #define NO_THREAD_SAFETY_ANALYSIS \
197 THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
199 //------------------------------------------------------------------------------
200 // Tool-Supplied Annotations
201 //------------------------------------------------------------------------------
203 // TS_UNCHECKED should be placed around lock expressions that are not valid
204 // C++ syntax, but which are present for documentation purposes. These
205 // annotations will be ignored by the analysis.
206 #define TS_UNCHECKED(x) ""
208 // TS_FIXME is used to mark lock expressions that are not valid C++ syntax.
209 // It is used by automated tools to mark and disable invalid expressions.
210 // The annotation should either be fixed, or changed to TS_UNCHECKED.
211 #define TS_FIXME(x) ""
213 // Like NO_THREAD_SAFETY_ANALYSIS, this turns off checking within the body of
214 // a particular function. However, this attribute is used to mark functions
215 // that are incorrect and need to be fixed. It is used by automated tools to
216 // avoid breaking the build when the analysis is updated.
217 // Code owners are expected to eventually fix the routine.
218 #define NO_THREAD_SAFETY_ANALYSIS_FIXME NO_THREAD_SAFETY_ANALYSIS
220 // Similar to NO_THREAD_SAFETY_ANALYSIS_FIXME, this macro marks a GUARDED_BY
221 // annotation that needs to be fixed, because it is producing thread safety
222 // warning. It disables the GUARDED_BY.
223 #define GUARDED_BY_FIXME(x)
225 // Disables warnings for a single read operation. This can be used to avoid
226 // warnings when it is known that the read is not actually involved in a race,
227 // but the compiler cannot confirm that.
228 #define TS_UNCHECKED_READ(x) thread_safety_analysis::ts_unchecked_read(x)
230 namespace thread_safety_analysis {
232 // Takes a reference to a guarded data member, and returns an unguarded
234 template <typename T>
235 inline const T& ts_unchecked_read(const T& v) NO_THREAD_SAFETY_ANALYSIS {
239 template <typename T>
240 inline T& ts_unchecked_read(T& v) NO_THREAD_SAFETY_ANALYSIS {
244 } // namespace thread_safety_analysis
246 // The above is imported as-is from abseil-cpp. The following Chromium-specific
247 // synonyms are added for Chromium concepts (SequenceChecker/ThreadChecker).
250 // Equivalent to GUARDED_BY for SequenceChecker/ThreadChecker. Currently,
251 #define GUARDED_BY_CONTEXT(name) GUARDED_BY(name)
253 // Equivalent to EXCLUSIVE_LOCKS_REQUIRED for SequenceChecker/ThreadChecker.
254 #define VALID_CONTEXT_REQUIRED(name) EXCLUSIVE_LOCKS_REQUIRED(name)
256 #else // DCHECK_IS_ON()
258 #define GUARDED_BY_CONTEXT(name)
259 #define VALID_CONTEXT_REQUIRED(name)
261 #endif // DCHECK_IS_ON()
263 #endif // BASE_THREAD_ANNOTATIONS_H_