From my reading of the test source, it seems to be testing the ability to do various async-signal-unsafe things after fork (but without execve) from a multithreaded parent, which has undefined behavior. Does Ruby (and Ruby programs) actually depend on the ability to do this, or is it just a gratuitous test for something that's not supposed to be supported usage. It looks dubious to me that Ruby even exposes a fork operation to the program it's executing; it's really hard to get forking of an interpreter right, and basically impossible if the interpreter process is allowed to be multi-threaded.