> The TCP URG bit came out of this kind of problem. It triggers a SIGURG signal on UNIX which interrupts the process. Oracle works this way.

https://datatracker.ietf.org/doc/html/rfc6093:

“it is strongly recommended that applications do not employ urgent indications. Nevertheless, urgent indications are still retained as a mandatory part of the TCP protocol to support the few legacy applications that employ them. However, it is expected that even these applications will have difficulties in environments with middleboxes.”