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 <h3 class="section">13.16 Interrupt-Driven Input</h3>

 <p><a name="index-interrupt_002ddriven-input-1378"></a>If you set the <code>O_ASYNC</code> status flag on a file descriptor
 (see <a href="File-Status-Flags.html#File-Status-Flags">File Status Flags</a>), a <code>SIGIO</code> signal is sent whenever
 input or output becomes possible on that file descriptor.  The process
 or process group to receive the signal can be selected by using the
 <code>F_SETOWN</code> command to the <code>fcntl</code> function.  If the file
 descriptor is a socket, this also selects the recipient of <code>SIGURG</code>
 signals that are delivered when out-of-band data arrives on that socket;
 see <a href="Out_002dof_002dBand-Data.html#Out_002dof_002dBand-Data">Out-of-Band Data</a>.  (<code>SIGURG</code> is sent in any situation
 where <code>select</code> would report the socket as having an &ldquo;exceptional
 condition&rdquo;.  See <a href="Waiting-for-I_002fO.html#Waiting-for-I_002fO">Waiting for I/O</a>.)

    <p>If the file descriptor corresponds to a terminal device, then <code>SIGIO</code>
 signals are sent to the foreground process group of the terminal.
 See <a href="Job-Control.html#Job-Control">Job Control</a>.

    <p><a name="index-fcntl_002eh-1379"></a>The symbols in this section are defined in the header file
 <samp><span class="file">fcntl.h</span></samp>.

 <!-- fcntl.h -->
 <!-- BSD -->
 <div class="defun">
 &mdash; Macro: int <b>F_GETOWN</b><var><a name="index-F_005fGETOWN-1380"></a></var><br>
 <blockquote><p>This macro is used as the <var>command</var> argument to <code>fcntl</code>, to
 specify that it should get information about the process or process
 group to which <code>SIGIO</code> signals are sent.  (For a terminal, this is
 actually the foreground process group ID, which you can get using
 <code>tcgetpgrp</code>; see <a href="Terminal-Access-Functions.html#Terminal-Access-Functions">Terminal Access Functions</a>.)

         <p>The return value is interpreted as a process ID; if negative, its
 absolute value is the process group ID.

         <p>The following <code>errno</code> error condition is defined for this command:

           <dl>
 <dt><code>EBADF</code><dd>The <var>filedes</var> argument is invalid.
 </dl>
         </p></blockquote></div>

 <!-- fcntl.h -->
 <!-- BSD -->
 <div class="defun">
 &mdash; Macro: int <b>F_SETOWN</b><var><a name="index-F_005fSETOWN-1381"></a></var><br>
 <blockquote><p>This macro is used as the <var>command</var> argument to <code>fcntl</code>, to
 specify that it should set the process or process group to which
 <code>SIGIO</code> signals are sent.  This command requires a third argument
 of type <code>pid_t</code> to be passed to <code>fcntl</code>, so that the form of
 the call is:

      <pre class="smallexample">          fcntl (<var>filedes</var>, F_SETOWN, <var>pid</var>)
 </pre>
         <p>The <var>pid</var> argument should be a process ID.  You can also pass a
 negative number whose absolute value is a process group ID.

         <p>The return value from <code>fcntl</code> with this command is -1
 in case of error and some other value if successful.  The following
 <code>errno</code> error conditions are defined for this command:

           <dl>
 <dt><code>EBADF</code><dd>The <var>filedes</var> argument is invalid.

           <br><dt><code>ESRCH</code><dd>There is no process or process group corresponding to <var>pid</var>.
 </dl>
         </p></blockquote></div>

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	of `The GNU C Library Reference Manual', for version
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	Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002,
	2003, 2007, 2008, 2010 Free Software Foundation, Inc.

	Permission is granted to copy, distribute and/or modify this document
	under the terms of the GNU Free Documentation License, Version 1.3 or
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	Invariant Sections being ``Free Software Needs Free Documentation''
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	Next: <a rel="next" accesskey="n" href="IOCTLs.html#IOCTLs">IOCTLs</a>,
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	<hr>
	</div>

	<h3 class="section">13.16 Interrupt-Driven Input</h3>

	<p><a name="index-interrupt_002ddriven-input-1378"></a>If you set the <code>O_ASYNC</code> status flag on a file descriptor
	(see <a href="File-Status-Flags.html#File-Status-Flags">File Status Flags</a>), a <code>SIGIO</code> signal is sent whenever
	input or output becomes possible on that file descriptor. The process
	or process group to receive the signal can be selected by using the
	<code>F_SETOWN</code> command to the <code>fcntl</code> function. If the file
	descriptor is a socket, this also selects the recipient of <code>SIGURG</code>
	signals that are delivered when out-of-band data arrives on that socket;
	see <a href="Out_002dof_002dBand-Data.html#Out_002dof_002dBand-Data">Out-of-Band Data</a>. (<code>SIGURG</code> is sent in any situation
	where <code>select</code> would report the socket as having an “exceptional
	condition”. See <a href="Waiting-for-I_002fO.html#Waiting-for-I_002fO">Waiting for I/O</a>.)

	<p>If the file descriptor corresponds to a terminal device, then <code>SIGIO</code>
	signals are sent to the foreground process group of the terminal.
	See <a href="Job-Control.html#Job-Control">Job Control</a>.

	<p><a name="index-fcntl_002eh-1379"></a>The symbols in this section are defined in the header file
	<samp><span class="file">fcntl.h</span></samp>.

	<!-- fcntl.h -->
	<!-- BSD -->
	<div class="defun">
	— Macro: int <b>F_GETOWN</b><var><a name="index-F_005fGETOWN-1380"></a></var><br>
	<blockquote><p>This macro is used as the <var>command</var> argument to <code>fcntl</code>, to
	specify that it should get information about the process or process
	group to which <code>SIGIO</code> signals are sent. (For a terminal, this is
	actually the foreground process group ID, which you can get using
	<code>tcgetpgrp</code>; see <a href="Terminal-Access-Functions.html#Terminal-Access-Functions">Terminal Access Functions</a>.)

	<p>The return value is interpreted as a process ID; if negative, its
	absolute value is the process group ID.

	<p>The following <code>errno</code> error condition is defined for this command:

	<dl>
	<dt><code>EBADF</code><dd>The <var>filedes</var> argument is invalid.
	</dl>
	</p></blockquote></div>

	<!-- fcntl.h -->
	<!-- BSD -->
	<div class="defun">
	— Macro: int <b>F_SETOWN</b><var><a name="index-F_005fSETOWN-1381"></a></var><br>
	<blockquote><p>This macro is used as the <var>command</var> argument to <code>fcntl</code>, to
	specify that it should set the process or process group to which
	<code>SIGIO</code> signals are sent. This command requires a third argument
	of type <code>pid_t</code> to be passed to <code>fcntl</code>, so that the form of
	the call is:

	<pre class="smallexample"> fcntl (<var>filedes</var>, F_SETOWN, <var>pid</var>)
	</pre>
	<p>The <var>pid</var> argument should be a process ID. You can also pass a
	negative number whose absolute value is a process group ID.

	<p>The return value from <code>fcntl</code> with this command is -1
	in case of error and some other value if successful. The following
	<code>errno</code> error conditions are defined for this command:

	<dl>
	<dt><code>EBADF</code><dd>The <var>filedes</var> argument is invalid.

	<br><dt><code>ESRCH</code><dd>There is no process or process group corresponding to <var>pid</var>.
	</dl>
	</p></blockquote></div>

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