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+//
+// Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS.  All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+//
+// Borrowed from
+// https://code.google.com/p/gperftools/source/browse/src/base/thread_annotations.h
+// but adapted for clang attributes instead of the gcc.
+//
+// This header file contains the macro definitions for thread safety
+// annotations that allow the developers to document the locking policies
+// of their multi-threaded code. The annotations can also help program
+// analysis tools to identify potential thread safety issues.
+
+#ifndef BASE_THREAD_ANNOTATIONS_H_
+#define BASE_THREAD_ANNOTATIONS_H_
+
+#if defined(__clang__) && (!defined(SWIG))
+#define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
+#else
+#define THREAD_ANNOTATION_ATTRIBUTE__(x)  // no-op
+#endif
+
+// Document if a shared variable/field needs to be protected by a lock.
+// GUARDED_BY allows the user to specify a particular lock that should be
+// held when accessing the annotated variable, while GUARDED_VAR only
+// indicates a shared variable should be guarded (by any lock). GUARDED_VAR
+// is primarily used when the client cannot express the name of the lock.
+#define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
+#define GUARDED_VAR THREAD_ANNOTATION_ATTRIBUTE__(guarded)
+
+// Document if the memory location pointed to by a pointer should be guarded
+// by a lock when dereferencing the pointer. Similar to GUARDED_VAR,
+// PT_GUARDED_VAR is primarily used when the client cannot express the name
+// of the lock. Note that a pointer variable to a shared memory location
+// could itself be a shared variable. For example, if a shared global pointer
+// q, which is guarded by mu1, points to a shared memory location that is
+// guarded by mu2, q should be annotated as follows:
+//     int *q GUARDED_BY(mu1) PT_GUARDED_BY(mu2);
+#define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(point_to_guarded_by(x))
+#define PT_GUARDED_VAR THREAD_ANNOTATION_ATTRIBUTE__(point_to_guarded)
+
+// Document the acquisition order between locks that can be held
+// simultaneously by a thread. For any two locks that need to be annotated
+// to establish an acquisition order, only one of them needs the annotation.
+// (i.e. You don't have to annotate both locks with both ACQUIRED_AFTER
+// and ACQUIRED_BEFORE.)
+#define ACQUIRED_AFTER(x) THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(x))
+#define ACQUIRED_BEFORE(x) THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(x))
+
+// The following three annotations document the lock requirements for
+// functions/methods.
+
+// Document if a function expects certain locks to be held before it is called
+#define EXCLUSIVE_LOCKS_REQUIRED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))
+
+#define SHARED_LOCKS_REQUIRED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))
+
+// Document the locks acquired in the body of the function. These locks
+// cannot be held when calling this function (as google3's Mutex locks are
+// non-reentrant).
+#define LOCKS_EXCLUDED(x) THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(x))
+
+// Document the lock the annotated function returns without acquiring it.
+#define LOCK_RETURNED(x) THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
+
+// Document if a class/type is a lockable type (such as the Mutex class).
+#define LOCKABLE THREAD_ANNOTATION_ATTRIBUTE__(lockable)
+
+// Document if a class is a scoped lockable type (such as the MutexLock class).
+#define SCOPED_LOCKABLE THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
+
+// The following annotations specify lock and unlock primitives.
+#define EXCLUSIVE_LOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))
+
+#define SHARED_LOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))
+
+#define EXCLUSIVE_TRYLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))
+
+#define SHARED_TRYLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))
+
+#define UNLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))
+
+// An escape hatch for thread safety analysis to ignore the annotated function.
+#define NO_THREAD_SAFETY_ANALYSIS \
+  THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
+
+#endif  // BASE_THREAD_ANNOTATIONS_H_