+@item
+This function is unsafe to call between @code{fork} and @code{exec} if
+the parent process is multi-threaded.
+@item
+It is unspecified whether the effective group id will be included in
+the returned list, nor whether the list will be sorted in any
+particular order. For that matter, some platforms include the
+effective group id twice, if it is also a member of the current
+supplemental group ids.