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The GNU C Library

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24.2.4 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 (see section 13.16 Interrupt-Driven 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. See section 16.9.8 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.


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