+namespace {
+
+#if FOLLY_HAVE_PTHREAD
+pthread_t stdTidToPthreadId(std::thread::id tid) {
+ static_assert(
+ std::is_same<pthread_t, std::thread::native_handle_type>::value,
+ "This assumes that the native handle type is pthread_t");
+ static_assert(
+ sizeof(std::thread::native_handle_type) == sizeof(std::thread::id),
+ "This assumes std::thread::id is a thin wrapper around "
+ "std::thread::native_handle_type, but that doesn't appear to be true.");
+ // In most implementations, std::thread::id is a thin wrapper around
+ // std::thread::native_handle_type, which means we can do unsafe things to
+ // extract it.
+ pthread_t id;
+ std::memcpy(&id, &tid, sizeof(id));
+ return id;
+}
+#endif
+
+} // namespace
+