It appears that Hubbe tested socketpair() and found it to return EAGAIN and EADDRINUSE on occasion on AmigaOS? Even though all the UNIX manpages list it as incapable of returning either EAGAIN or EADDRINUSE? Anyone here who can still recall the circumstances?
AmigaOS (at the time, not sure about now) probably doesn't have true AF_UNIX sockets, and simulates them with AF_INET sockets (just like socketpair_ultra), which can run out of ports on the loopback-interface, which will fail with EADDRINUSE. Note the following comment in src/modules/files/file.c:
/* Don't try to use socketpair() on AmigaOS, socketpair_ultra works better */
BTW: I don't believe Hubbe ever compiled Pike for AmigaOS himself, but that most of the AmigaOS patches came from Bernhard Fastenrath and Marcus Comstedt. I seem to remember Bernhard Fastenrath reporting lots of bugs in ixemul.library that Pike's testsuite detected.