Expressed the thread-safety annotations in code, replacing the existing comment-based system (by Aaron Jacobs).

include/gtest/internal/gtest-linked_ptr.h

@@ -105,8 +105,8 @@ class linked_ptr_internal {
   // framework.
 
   // Join an existing circle.
-  // L < g_linked_ptr_mutex
-  void join(linked_ptr_internal const* ptr) {
+  void join(linked_ptr_internal const* ptr)
+      GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
     MutexLock lock(&g_linked_ptr_mutex);
 
     linked_ptr_internal const* p = ptr;
@@ -117,8 +117,8 @@ class linked_ptr_internal {
 
   // Leave whatever circle we're part of.  Returns true if we were the
   // last member of the circle.  Once this is done, you can join() another.
-  // L < g_linked_ptr_mutex
-  bool depart() {
+  bool depart()
+      GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
     MutexLock lock(&g_linked_ptr_mutex);
 
     if (next_ == this) return true;

include/gtest/internal/gtest-port.h

@@ -1789,6 +1789,10 @@ typedef TypeWithSize<8>::Int TimeInMillis;  // Represents time in milliseconds.
 #define GTEST_DEFINE_string_(name, default_val, doc) \
     GTEST_API_ ::testing::internal::String GTEST_FLAG(name) = (default_val)
 
+// Thread annotations
+#define GTEST_EXCLUSIVE_LOCK_REQUIRED_(locks)
+#define GTEST_LOCK_EXCLUDED_(locks)
+
 // Parses 'str' for a 32-bit signed integer.  If successful, writes the result
 // to *value and returns true; otherwise leaves *value unchanged and returns
 // false.