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<body>
<div id="header">
<h1>
zmq_poll(3) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>zmq_poll -
input/output multiplexing
</p>
</div>
</div>
<div id="content">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="paragraph"><p><strong>int zmq_poll (zmq_pollitem_t <em>*items</em>, int <em>nitems</em>, long <em>timeout</em>);</strong></p></div>
</div>
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph"><p>The <em>zmq_poll()</em> function provides a mechanism for applications to multiplex
input/output events in a level-triggered fashion over a set of sockets. Each
member of the array pointed to by the <em>items</em> argument is a <strong>zmq_pollitem_t</strong>
structure. The <em>nitems</em> argument specifies the number of items in the <em>items</em>
array. The <strong>zmq_pollitem_t</strong> structure is defined as follows:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>typedef struct
{
void <em>*socket</em>;
int <em>fd</em>;
short <em>events</em>;
short <em>revents</em>;
} zmq_pollitem_t;</tt></pre>
</div></div>
<div class="paragraph"><p>For each <strong>zmq_pollitem_t</strong> item, <em>zmq_poll()</em> shall examine either the ØMQ
socket referenced by <em>socket</em> <strong>or</strong> the standard socket specified by the file
descriptor <em>fd</em>, for the event(s) specified in <em>events</em>. If both <em>socket</em> and
<em>fd</em> are set in a single <strong>zmq_pollitem_t</strong>, the ØMQ socket referenced by
<em>socket</em> shall take precedence and the value of <em>fd</em> shall be ignored.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">All ØMQ sockets passed to the <em>zmq_poll()</em> function must share the
same ØMQ <em>context</em> and must belong to the thread calling <em>zmq_poll()</em>.</td>
</tr></table>
</div>
<div class="paragraph"><p>For each <strong>zmq_pollitem_t</strong> item, <em>zmq_poll()</em> shall first clear the <em>revents</em>
member, and then indicate any requested events that have occurred by setting the
bit corresponding to the event condition in the <em>revents</em> member.</p></div>
<div class="paragraph"><p>If none of the requested events have occurred on any <strong>zmq_pollitem_t</strong> item,
<em>zmq_poll()</em> shall wait <em>timeout</em> microseconds for an event to occur on
any of the requested items. If the value of <em>timeout</em> is <tt>0</tt>, <em>zmq_poll()</em>
shall return immediately. If the value of <em>timeout</em> is <tt>-1</tt>, <em>zmq_poll()</em> shall
block indefinitely until a requested event has occurred on at least one
<strong>zmq_pollitem_t</strong>. The resolution of <em>timeout</em> is 1 millisecond.</p></div>
<div class="paragraph"><p>The <em>events</em> and <em>revents</em> members of <strong>zmq_pollitem_t</strong> are bit masks constructed
by OR’ing a combination of the following event flags:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>ZMQ_POLLIN</strong>
</dt>
<dd>
<p>
For ØMQ sockets, at least one message may be received from the <em>socket</em> without
blocking. For standard sockets this is equivalent to the <em>POLLIN</em> flag of the
<em>poll()</em> system call and generally means that at least one byte of data may be
read from <em>fd</em> without blocking.
</p>
</dd>
<dt class="hdlist1">
<strong>ZMQ_POLLOUT</strong>
</dt>
<dd>
<p>
For ØMQ sockets, at least one message may be sent to the <em>socket</em> without
blocking. For standard sockets this is equivalent to the <em>POLLOUT</em> flag of the
<em>poll()</em> system call and generally means that at least one byte of data may be
written to <em>fd</em> without blocking.
</p>
</dd>
<dt class="hdlist1">
<strong>ZMQ_POLLERR</strong>
</dt>
<dd>
<p>
For standard sockets, this flag is passed through <em>zmq_poll()</em> to the
underlying <em>poll()</em> system call and generally means that some sort of error
condition is present on the socket specified by <em>fd</em>. For ØMQ sockets this flag
has no effect if set in <em>events</em>, and shall never be returned in <em>revents</em> by
<em>zmq_poll()</em>.
</p>
</dd>
</dl></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">The <em>zmq_poll()</em> function may be implemented or emulated using operating
system interfaces other than <em>poll()</em>, and as such may be subject to the limits
of those interfaces in ways not defined in this documentation.</td>
</tr></table>
</div>
</div>
<h2 id="_return_value">RETURN VALUE</h2>
<div class="sectionbody">
<div class="paragraph"><p>Upon successful completion, the <em>zmq_poll()</em> function shall return the number
of <strong>zmq_pollitem_t</strong> structures with events signaled in <em>revents</em> or <tt>0</tt> if no
events have been signaled. Upon failure, <em>zmq_poll()</em> shall return <tt>-1</tt> and set
<em>errno</em> to one of the values defined below.</p></div>
</div>
<h2 id="_errors">ERRORS</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
<strong>ETERM</strong>
</dt>
<dd>
<p>
At least one of the members of the <em>items</em> array refers to a <em>socket</em> whose
associated ØMQ <em>context</em> was terminated.
</p>
</dd>
<dt class="hdlist1">
<strong>EFAULT</strong>
</dt>
<dd>
<p>
The provided <em>items</em> was not valid (NULL).
</p>
</dd>
<dt class="hdlist1">
<strong>EINTR</strong>
</dt>
<dd>
<p>
The operation was interrupted by delivery of a signal before any events were
available.
</p>
</dd>
</dl></div>
</div>
<h2 id="_example">EXAMPLE</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="title">Polling indefinitely for input events on both a ØMQ socket and a standard socket.</div>
<div class="content">
<pre><tt>zmq_pollitem_t items [2];
/* First item refers to 0MQ socket 'socket' */
items[0].socket = socket;
items[0].events = ZMQ_POLLIN;
/* Second item refers to standard socket 'fd' */
items[1].socket = NULL;
items[1].fd = fd;
items[1].events = ZMQ_POLLIN;
/* Poll for events indefinitely */
int rc = zmq_poll (items, 2, -1);
assert (rc >= 0);
/* Returned events will be stored in items[].revents */</tt></pre>
</div></div>
</div>
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="zmq_socket.html">zmq_socket(3)</a>
<a href="zmq_send.html">zmq_send(3)</a>
<a href="zmq_recv.html">zmq_recv(3)</a>
<a href="zmq.html">zmq(7)</a></p></div>
<div class="paragraph"><p>Your operating system documentation for the <em>poll()</em> system call.</p></div>
</div>
<h2 id="_authors">AUTHORS</h2>
<div class="sectionbody">
<div class="paragraph"><p>This ØMQ manual page was written by Martin Sustrik <<a href="mailto:sustrik@250bpm.com">sustrik@250bpm.com</a>> and
Martin Lucina <<a href="mailto:mato@kotelna.sk">mato@kotelna.sk</a>>.</p></div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
ØMQ 2.1.10<br />
Last updated 2011-08-23 16:01:49 CDT
</div>
</div>
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