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A pointer to a valid poller must be passed as the <em>poller_p</em> argument of <em>zmq_poller_destroy</em>. In particular, <em>zmq_poller_destroy</em> may not be called multiple times for the same poller instance. <em>zmq_poller_destroy</em> sets the passed pointer to NULL in case of a successful execution. <em>zmq_poller_destroy</em> implicitly unregisters all registered sockets and file descriptors.</p></div> <div class="paragraph"><p><em>zmq_poller_add</em>, <em>zmq_poller_modify</em> and <em>zmq_poller_remove</em> manage the ØMQ sockets registered with a poller.</p></div> <div class="paragraph"><p><em>zmq_poller_add</em> registers a new <em>socket</em> with a given <em>poller</em>. Both <em>poller</em> and <em>socket</em> must point to valid ØMQ objects. The <em>events</em> parameter specifies which event types the client wants to subscribe to. It is legal to specify no events (i.e. 0), and activate them later with <em>zmq_poller_modify</em>. In addition, <em>user_data</em> may be specified, which is not used by the poller, but passed back to the caller when an event was signalled in a call to <em>zmq_poller_wait</em> or <em>zmq_poller_wait_all</em>. <em>user_data</em> may be NULL. If it is not NULL, it must be a valid pointer. Otherwise, behaviour is undefined. <em>zmq_poller_add</em> may not be called multiple times for the same socket (unless <em>zmq_poller_remove</em> has been called for that socket).</p></div> <div class="paragraph"><p><em>zmq_poller_modify</em> modifies the subscribed events for a socket. It is legal to specify no events (i.e. 0) to disable events temporarily, and reactivate them later with another call to <em>zmq_poller_modify</em>.</p></div> <div class="paragraph"><p><em>zmq_poller_remove</em> removes a socket registration completely. <em>zmq_poller_remove</em> must be called before a socket is closed with <em>zmq_close</em>.</p></div> <div class="paragraph"><p>Note that it is not necessary to call <em>zmq_poller_remove</em> for any socket before calling <em>zmq_poller_destroy</em>.</p></div> <div class="paragraph"><p>Also note that calling <em>zmq_poller_remove</em> is not equivalent to calling <em>zmq_poller_modify</em> with no events. <em>zmq_poller_modify</em> does not free resources associated with the socket registration, and requires that the <em>socket</em> remains valid.</p></div> <div class="paragraph"><p><em>zmq_poller_add_fd</em>, <em>zmq_poller_modify_fd</em> and <em>zmq_poller_remove_fd</em> are analogous to the previous functions but manage regular file descriptiors registered with a poller. On Windows, these functions can only be used with WinSock sockets.</p></div> <div class="paragraph"><p>In the following, ØMQ sockets added with <em>zmq_poller_add</em> and file descriptors added with <em>zmq_poller_add_fd</em> are referred to as <em>registered objects</em>.</p></div> <div class="paragraph"><p>The <strong>zmq_poller_event_t</strong> structure is defined as follows:</p></div> <div class="literalblock"> <div class="content"> <pre><code>typedef struct { void *socket; #if defined _WIN32 SOCKET fd; #else int fd; #endif void *user_data; short events; } zmq_poller_event_t;</code></pre> </div></div> <div class="paragraph"><p>For each registered object, <em>zmq_poller_wait_all()</em> shall examine the registered objects for the event(s) currently registered.</p></div> <div class="paragraph"><p>If none of the registered events have occurred, <em>zmq_poller_wait_all</em> shall wait <em>timeout</em> milliseconds for an event to occur on any of the registered objects. If the value of <em>timeout</em> is <code>0</code>, <em>zmq_poller_wait_all</em> shall return immediately. If the value of <em>timeout</em> is <code>-1</code>, <em>zmq_poller_wait_all</em> shall block indefinitely until one event has occurred on any of the registered objects.</p></div> <div class="paragraph"><p>The <em>events</em> argument <em>zmq_poller_wait_all</em> must be a pointer to an array of at least <em>n_events</em> elements. Behaviour is undefined if <em>events</em> does not point to an array of at least <em>n_events</em> elements.</p></div> <div class="paragraph"><p><em>zmq_poller_wait_all</em> returns at most <em>n_events</em> events. If more than <em>n_events</em> events were signalled, only an unspecified subset of the signalled events is returned through <em>events</em>.</p></div> <div class="paragraph"><p>A caller is advised to ensure that <em>n_events</em> is equal to the number of registered objects. Otherwise, a livelock situation may result: If more than <em>n_events</em> registered objects have an active event on each call to <em>zmq_poller_wait_all</em>, it might happen that the same subset of registered objects is always returned, and the caller never notices the events on the others.</p></div> <div class="paragraph"><p><em>zmq_poller_wait_all</em> returns the number of valid elements. The valid elements are placed in positions <em>0</em> to <em>n_events - 1</em> in the <em>events</em> array. All members of a valid element are set to valid values by <em>zmq_poller_wait_all</em>. The client does therefore not need to initialize the contents of the events array before a call to <em>zmq_poller_wait_all</em>. It is unspecified whether the the remaining elements of <em>events</em> are written to by <em>zmq_poller_wait_all</em>.</p></div> </div> </div> <div class="sect1"> <h2 id="_event_types">EVENT TYPES</h2> <div class="sectionbody"> <div class="paragraph"><p>The <em>events</em> parameter of <em>zmq_poller_add</em> and <em>zmq_poller_modify</em>, and the <em>events</em> member of the zmq_poller_event_t structure 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 ØMQ sockets this flag has no effect on the <em>zmq_poller_add</em> and <em>zmq_poller_modify</em> functions, and is never set in the <em>events</em> member of the zmq_poller_event_t structure. For standard sockets, this flag is passed through <em>zmq_poller_wait_all</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>. </p> </dd> <dt class="hdlist1"> <strong>ZMQ_POLLPRI</strong> </dt> <dd> <p> For ØMQ sockets this flag has no effect on the <em>zmq_poller_add</em> and <em>zmq_poller_modify</em> functions, and is never set in the <em>events</em> member of the zmq_poller_event_t structure. For standard sockets this means there is urgent data to read. Refer to the POLLPRI flag for more informations. For a file descriptor, refer to your OS documentation: 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_poller</em>*_ functions 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="_thread_safety">THREAD SAFETY</h2> <div class="sectionbody"> <div class="paragraph"><p>Like most other ØMQ objects, a poller is not thread-safe. All operations must be called from the same thread. Otherwise, behaviour is undefined.</p></div> </div> </div> <div class="sect1"> <h2 id="_return_value">RETURN VALUE</h2> <div class="sectionbody"> <div class="paragraph"><p><em>zmq_poller_new</em> always returns a valid pointer to a poller.</p></div> <div class="paragraph"><p>All functions that return an int, return -1 in case of a failure. In that case, zmq_errno() can be used to query the type of the error as described below.</p></div> <div class="paragraph"><p><em>zmq_poller_wait_all</em> returns the number of events signalled and returned in the events array. It never returns 0.</p></div> <div class="paragraph"><p>All other functions return 0 in case of a successful execution.</p></div> </div> </div> <div class="sect1"> <h2 id="_errors">ERRORS</h2> <div class="sectionbody"> <div class="paragraph"><p>On <em>zmq_poller_new</em>: <strong>ENOMEM</strong>:: A new poller could not be allocated successfully.</p></div> <div class="paragraph"><p>On <em>zmq_poller_destroy</em>: <strong>EFAULT</strong>:: <em>poller_p</em> did not point to a valid poller. Note that passing an invalid pointer (e.g. pointer to deallocated memory) may cause undefined behaviour (e.g. an access violation).</p></div> <div class="paragraph"><p>On <em>zmq_poller_add</em>, <em>zmq_poller_modify</em> and <em>zmq_poller_remove</em>: <strong>EFAULT</strong>:: <em>poller</em> did not point to a valid poller. Note that passing an invalid pointer (e.g. pointer to deallocated memory) may cause undefined behaviour (e.g. an access violation). <strong>ENOTSOCK</strong>:: <em>socket</em> did not point to a valid socket. Note that passing an invalid pointer (e.g. pointer to deallocated memory) may cause undefined behaviour (e.g. an access violation).</p></div> <div class="paragraph"><p>On <em>zmq_poller_add</em>: <strong>EMFILE</strong>:: TODO</p></div> <div class="paragraph"><p>On <em>zmq_poller_add</em> or <em>zmq_poller_add_fd</em>: <strong>ENOMEM</strong>:: Necessary resources could not be allocated. <strong>EINVAL</strong>:: <em>socket</em> resp. <em>fd</em> was already registered with the poller.</p></div> <div class="paragraph"><p>On <em>zmq_poller_modify</em>, <em>zmq_poller_modify_fd</em>, <em>zmq_poller_remove</em> or <em>zmq_poller_remove_fd</em>: <strong>EINVAL</strong>:: <em>socket</em> resp. <em>fd</em> was not registered with the poller.</p></div> <div class="paragraph"><p>On <em>zmq_poller_add_fd</em>, <em>zmq_poller_modify_fd</em> and <em>zmq_poller_remove_fd</em>: <strong>EBADF</strong>*: The <em>fd</em> specified was the retired fd.</p></div> <div class="paragraph"><p>On <em>zmq_poller_wait</em> and <em>zmq_poller_wait_all</em>: <strong>ETERM</strong>:: At least one of the registered objects is a <em>socket</em> whose associated ØMQ <em>context</em> was terminated. <strong>EFAULT</strong>:: The provided <em>events</em> was NULL, or <em>poller</em> did not point to a valid poller, or there are no registered objects and <em>timeout</em> was negative. <strong>EINTR</strong>:: The operation was interrupted by delivery of a signal before any events were available. <strong>EAGAIN</strong>:: No registered event was signalled before the timeout was reached.</p></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>void *poller = zmq_poller_new (); zmq_poller_event_t events [2]; /* First item refers to 0MQ socket 'socket' */ zmq_poller_add (poller, socket, ZMQ_POLLIN, NULL); /* Second item refers to standard socket 'fd' */ zmq_poller_add_fd (poller, fd, ZMQ_POLLIN, NULL); /* Poll for events indefinitely */ int rc = zmq_poller_wait_all (items, events, 2, -1); assert (rc >= 0); /* Returned events will be stored in 'events' */ zmq_poller_destroy (&poller);</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> </div> <div class="sect1"> <h2 id="_authors">AUTHORS</h2> <div class="sectionbody"> <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> </div> </div> </div> <div id="footnotes"><hr /></div> <div id="footer"> <div id="footer-text"> ØMQ 4.3.1<br /> Last updated 2019-01-12 16:17:39 UTC </div> </div> </body> </html>