CZMQ Manual - CZMQ/4.0.3


zpoller - Class for trivial socket poller class


//  This is a stable class, and may not change except for emergencies. It
//  is provided in stable builds.
//  Create new poller, specifying zero or more readers. The list of
//  readers ends in a NULL. Each reader can be a zsock_t instance, a
//  zactor_t instance, a libzmq socket (void *), or a file handle.
CZMQ_EXPORT zpoller_t *
    zpoller_new (void *reader, ...);

//  Destroy a poller
    zpoller_destroy (zpoller_t **self_p);

//  Add a reader to be polled. Returns 0 if OK, -1 on failure. The reader may
//  be a libzmq void * socket, a zsock_t instance, or a zactor_t instance.
    zpoller_add (zpoller_t *self, void *reader);

//  Remove a reader from the poller; returns 0 if OK, -1 on failure. The reader
//  must have been passed during construction, or in an zpoller_add () call.
    zpoller_remove (zpoller_t *self, void *reader);

//  By default the poller stops if the process receives a SIGINT or SIGTERM
//  signal. This makes it impossible to shut-down message based architectures
//  like zactors. This method lets you switch off break handling. The default
//  nonstop setting is off (false).
    zpoller_set_nonstop (zpoller_t *self, bool nonstop);

//  Poll the registered readers for I/O, return first reader that has input.
//  The reader will be a libzmq void * socket, or a zsock_t or zactor_t
//  instance as specified in zpoller_new/zpoller_add. The timeout should be
//  zero or greater, or -1 to wait indefinitely. Socket priority is defined
//  by their order in the poll list. If you need a balanced poll, use the low
//  level zmq_poll method directly. If the poll call was interrupted (SIGINT),
//  or the ZMQ context was destroyed, or the timeout expired, returns NULL.
//  You can test the actual exit condition by calling zpoller_expired () and
//  zpoller_terminated (). The timeout is in msec.
    zpoller_wait (zpoller_t *self, int timeout);

//  Return true if the last zpoller_wait () call ended because the timeout
//  expired, without any error.
    zpoller_expired (zpoller_t *self);

//  Return true if the last zpoller_wait () call ended because the process
//  was interrupted, or the parent context was destroyed.
    zpoller_terminated (zpoller_t *self);

//  Self test of this class.
    zpoller_test (bool verbose);

Please add '@interface' section in './../src/zpoller.c'.


The zpoller class provides a minimalist interface to ZeroMQ's zmq_poll API, for the very common case of reading from a number of sockets. It does not provide polling for output, nor polling on file handles. If you need either of these, use the zmq_poll API directly.

The class implements the poller using the zmq_poller API if that exists, else does the work itself.


From zpoller_test method

// Create a few sockets
zsock_t *vent = zsock_new (ZMQ_PUSH);
assert (vent);
int port_nbr = zsock_bind (vent, "tcp://*");
assert (port_nbr != -1);
zsock_t *sink = zsock_new (ZMQ_PULL);
assert (sink);
int rc = zsock_connect (sink, "tcp://", port_nbr);
assert (rc != -1);
zsock_t *bowl = zsock_new (ZMQ_PULL);
assert (bowl);
zsock_t *dish = zsock_new (ZMQ_PULL);
assert (dish);

// Set up poller
zpoller_t *poller = zpoller_new (bowl, dish, NULL);
assert (poller);

// Add a reader to the existing poller
rc = zpoller_add (poller, sink);
assert (rc == 0);

zstr_send (vent, "Hello, World");

// We expect a message only on the sink
zsock_t *which = (zsock_t *) zpoller_wait (poller, -1);
assert (which == sink);
assert (zpoller_expired (poller) == false);
assert (zpoller_terminated (poller) == false);
char *message = zstr_recv (which);
assert (streq (message, "Hello, World"));
zstr_free (&message);

// Stop polling reader
rc = zpoller_remove (poller, sink);
assert (rc == 0);

// Removing a non-existent reader shall fail
rc = zpoller_remove (poller, sink);
assert (rc == -1);
assert (errno == EINVAL);

// Check we can poll an FD
rc = zsock_connect (bowl, "tcp://", port_nbr);
assert (rc != -1);
SOCKET fd = zsock_fd (bowl);
rc = zpoller_add (poller, (void *) &fd);
assert (rc != -1);
zstr_send (vent, "Hello again, world");
assert (zpoller_wait (poller, 500) == &fd);

// Check zpoller_set_nonstop ()
zsys_interrupted = 1;
zpoller_wait (poller, 0);
assert (zpoller_terminated (poller));
zpoller_set_nonstop (poller, true);
zpoller_wait (poller, 0);
assert (!zpoller_terminated (poller));
zsys_interrupted = 0;

zpoller_destroy (&poller);
zsock_destroy (&vent);
zsock_destroy (&sink);
zsock_destroy (&bowl);
zsock_destroy (&dish);

// Check thread safe sockets
zpoller_destroy (&poller);
zsock_t *client = zsock_new (ZMQ_CLIENT);
assert (client);
zsock_t *server = zsock_new (ZMQ_SERVER);
assert (server);
poller = zpoller_new (client, server, NULL);
assert (poller);
port_nbr = zsock_bind (server, "tcp://*");
assert (port_nbr != -1);
rc = zsock_connect (client, "tcp://", port_nbr);
assert (rc != -1);

zstr_send (client, "Hello, World");

// We expect a message only on the server
which = (zsock_t *) zpoller_wait (poller, -1);
assert (which == server);
assert (zpoller_expired (poller) == false);
assert (zpoller_terminated (poller) == false);
message = zstr_recv (which);
assert (streq (message, "Hello, World"));
zstr_free (&message);

zpoller_destroy (&poller);
zsock_destroy (&client);
zsock_destroy (&server);

#if defined (__WINDOWS__)
zsys_shutdown(); #endif


The czmq manual was written by the authors in the AUTHORS file.


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Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for ØMQ: http://czmq.zeromq.org. This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/. LICENSE included with the czmq distribution.