Asynchronous I/O Signals
------------------------
The signals listed in this section are used in conjunction with
asynchronous I/O facilities. You have to take explicit action by
calling `fcntl' to enable a particular file descriptor to generate
these signals (Note:Interrupt Input). The default action for these
signals is to ignore them.
- Macro: int SIGIO
This signal is sent when a file descriptor is ready to perform
input or output.
On most operating systems, terminals and sockets are the only
kinds of files that can generate `SIGIO'; other kinds, including
ordinary files, never generate `SIGIO' even if you ask them to.
In the GNU system `SIGIO' will always be generated properly if you
successfully set asynchronous mode with `fcntl'.
- Macro: int SIGURG
This signal is sent when "urgent" or out-of-band data arrives on a
socket. Note:Out-of-Band Data.
- Macro: int SIGPOLL
This is a System V signal name, more or less similar to `SIGIO'.
It is defined only for compatibility.