Bug #14009: macOS High Sierra and “fork” compatibility - Ruby - Ruby Issue Tracking System

Perhaps it helps if I further clarify this issue for those who are unfamiliar with it. As you probably already know, forking (but without exec'ing) in a multithreaded environment is inherently dangerous and the environment must be carefully written to support such a thing. Apple's Objective-C libraries have traditionally not supported being called in a forked (but not exec'd) child process at all,