FCNTL

The FCNTL call controls the operating characteristics of a specified socket.

SOCKET FCNTL,(socket,cmd,arg)
socket
is the address of a fullword integer socket descriptor.
cmd
is the address of a fullword containing the command to perform:
F_SETFL
Sets socket flags. FNDELAY, which is the only valid flag, sets the socket in nonblocking mode.
F_GETFL
Queries the status of socket flags.
arg
is the address of a fullword containing the address of the data argument associated with the command. Only 0 and FNDELAY are supported.
rc
(Output) is a value returned when the socket call completes successfully for the F_GETFL command, which contains the flags set as a bit mask.