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<body class="manpage">
<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">
<div class="sect1">
<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>
</div>
<div class="sect1">
<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><code>typedef struct
{
void <em>*socket</em>;
int <em>fd</em>;
short <em>events</em>;
short <em>revents</em>;
} zmq_pollitem_t;</code></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="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> milliseconds for an event to occur on
any of the requested items. If the value of <em>timeout</em> is <code>0</code>, <em>zmq_poll()</em>
shall return immediately. If the value of <em>timeout</em> is <code>-1</code>, <em>zmq_poll()</em> shall
block indefinitely until a requested event has occurred on at least one
<strong>zmq_pollitem_t</strong>.</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>
<dt class="hdlist1">
<strong>ZMQ_POLLPRI</strong>
</dt>
<dd>
<p>
For ØMQ sockets this flags is of no use. For standard sockets this means there
is urgent data to read. Refer to the POLLPRI flag for more informations.
For file descriptor, refer to your use case: as an example, GPIO interrupts
are signaled through a POLLPRI event.
This flag has no effect on Windows.
</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>
</div>
<div class="sect1">
<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 <code>0</code> if no
events have been signaled. Upon failure, <em>zmq_poll()</em> shall return <code>-1</code> and set
<em>errno</em> to one of the values defined below.</p></div>
</div>
</div>
<div class="sect1">
<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>
</div>
<div class="sect1">
<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><code>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 */</code></pre>
</div></div>
</div>
</div>
<div class="sect1">
<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>
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<h2 id="_authors">AUTHORS</h2>
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<div class="paragraph"><p>This page was written by the ØMQ community. To make a change please
read the ØMQ Contribution Policy at <a href="http://www.zeromq.org/docs:contributing">http://www.zeromq.org/docs:contributing</a>.</p></div>
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ØMQ 4.3.2<br />
Last updated 2019-07-08 16:19:27 UTC
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