Scroll to navigation



zloop - Class for event-driven reactor


//  This is a stable class, and may not change except for emergencies. It
//  is provided in stable builds.
// Callback function for reactor socket activity
typedef int (zloop_reader_fn) (

zloop_t *loop, zsock_t *reader, void *arg); // Callback function for reactor events (low-level) typedef int (zloop_fn) (
zloop_t *loop, zmq_pollitem_t *item, void *arg); // Callback for reactor timer events typedef int (zloop_timer_fn) (
zloop_t *loop, int timer_id, void *arg); // Create a new zloop reactor CZMQ_EXPORT zloop_t *
zloop_new (void); // Destroy a reactor CZMQ_EXPORT void
zloop_destroy (zloop_t **self_p); // Register socket reader with the reactor. When the reader has messages, // the reactor will call the handler, passing the arg. Returns 0 if OK, -1 // if there was an error. If you register the same socket more than once, // each instance will invoke its corresponding handler. CZMQ_EXPORT int
zloop_reader (zloop_t *self, zsock_t *sock, zloop_reader_fn handler, void *arg); // Cancel a socket reader from the reactor. If multiple readers exist for // same socket, cancels ALL of them. CZMQ_EXPORT void
zloop_reader_end (zloop_t *self, zsock_t *sock); // Configure a registered reader to ignore errors. If you do not set this, // then readers that have errors are removed from the reactor silently. CZMQ_EXPORT void
zloop_reader_set_tolerant (zloop_t *self, zsock_t *sock); // Register low-level libzmq pollitem with the reactor. When the pollitem // is ready, will call the handler, passing the arg. Returns 0 if OK, -1 // if there was an error. If you register the pollitem more than once, each // instance will invoke its corresponding handler. A pollitem with // socket=NULL and fd=0 means 'poll on FD zero'. CZMQ_EXPORT int
zloop_poller (zloop_t *self, zmq_pollitem_t *item, zloop_fn handler, void *arg); // Cancel a pollitem from the reactor, specified by socket or FD. If both // are specified, uses only socket. If multiple poll items exist for same // socket/FD, cancels ALL of them. CZMQ_EXPORT void
zloop_poller_end (zloop_t *self, zmq_pollitem_t *item); // Configure a registered poller to ignore errors. If you do not set this, // then poller that have errors are removed from the reactor silently. CZMQ_EXPORT void
zloop_poller_set_tolerant (zloop_t *self, zmq_pollitem_t *item); // Register a timer that expires after some delay and repeats some number of // times. At each expiry, will call the handler, passing the arg. To run a // timer forever, use 0 times. Returns a timer_id that is used to cancel the // timer in the future. Returns -1 if there was an error. CZMQ_EXPORT int
zloop_timer (zloop_t *self, size_t delay, size_t times, zloop_timer_fn handler, void *arg); // Cancel a specific timer identified by a specific timer_id (as returned by // zloop_timer). CZMQ_EXPORT int
zloop_timer_end (zloop_t *self, int timer_id); // Register a ticket timer. Ticket timers are very fast in the case where // you use a lot of timers (thousands), and frequently remove and add them. // The main use case is expiry timers for servers that handle many clients, // and which reset the expiry timer for each message received from a client. // Whereas normal timers perform poorly as the number of clients grows, the // cost of ticket timers is constant, no matter the number of clients. You // must set the ticket delay using zloop_set_ticket_delay before creating a // ticket. Returns a handle to the timer that you should use in // zloop_ticket_reset and zloop_ticket_delete. CZMQ_EXPORT void *
zloop_ticket (zloop_t *self, zloop_timer_fn handler, void *arg); // Reset a ticket timer, which moves it to the end of the ticket list and // resets its execution time. This is a very fast operation. CZMQ_EXPORT void
zloop_ticket_reset (zloop_t *self, void *handle); // Delete a ticket timer. We do not actually delete the ticket here, as // other code may still refer to the ticket. We mark as deleted, and remove // later and safely. CZMQ_EXPORT void
zloop_ticket_delete (zloop_t *self, void *handle); // Set the ticket delay, which applies to all tickets. If you lower the // delay and there are already tickets created, the results are undefined. CZMQ_EXPORT void
zloop_set_ticket_delay (zloop_t *self, size_t ticket_delay); // Set hard limit on number of timers allowed. Setting more than a small // number of timers (10-100) can have a dramatic impact on the performance // of the reactor. For high-volume cases, use ticket timers. If the hard // limit is reached, the reactor stops creating new timers and logs an // error. CZMQ_EXPORT void
zloop_set_max_timers (zloop_t *self, size_t max_timers); // Set verbose tracing of reactor on/off. The default verbose setting is // off (false). CZMQ_EXPORT void
zloop_set_verbose (zloop_t *self, bool verbose); // By default the reactor 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). CZMQ_EXPORT void
zloop_set_nonstop (zloop_t *self, bool nonstop); // Start the reactor. Takes control of the thread and returns when the 0MQ // context is terminated or the process is interrupted, or any event handler // returns -1. Event handlers may register new sockets and timers, and // cancel sockets. Returns 0 if interrupted, -1 if canceled by a handler. CZMQ_EXPORT int
zloop_start (zloop_t *self); // Self test of this class. CZMQ_EXPORT void
zloop_test (bool verbose); Please add '@interface' section in './../src/zloop.c'.


The zloop class provides an event-driven reactor pattern. The reactor handles zmq_pollitem_t items (pollers or writers, sockets or fds), and once-off or repeated timers. Its resolution is 1 msec. It uses a tickless timer to reduce CPU interrupts in inactive processes.

Please add @discuss section in ./../src/zloop.c.


From zloop_test method.

//  Create two PAIR sockets and connect over inproc
zsock_t *output = zsock_new (ZMQ_PAIR);
assert (output);
zsock_bind (output, "inproc://zloop.test");
zsock_t *input = zsock_new (ZMQ_PAIR);
assert (input);
zsock_connect (input, "inproc://zloop.test");
zloop_t *loop = zloop_new ();
assert (loop);
zloop_set_verbose (loop, verbose);
//  Create a timer that will be cancelled
int timer_id = zloop_timer (loop, 1000, 1, s_timer_event, NULL);
zloop_timer (loop, 5, 1, s_cancel_timer_event, &timer_id);
//  After 20 msecs, send a ping message to output3
zloop_timer (loop, 20, 1, s_timer_event, output);
//  Set up some tickets that will never expire
zloop_set_ticket_delay (loop, 10000);
void *ticket1 = zloop_ticket (loop, s_timer_event, NULL);
void *ticket2 = zloop_ticket (loop, s_timer_event, NULL);
void *ticket3 = zloop_ticket (loop, s_timer_event, NULL);
//  When we get the ping message, end the reactor
rc = zloop_reader (loop, input, s_socket_event, NULL);
assert (rc == 0);
zloop_reader_set_tolerant (loop, input);
zloop_start (loop);
zloop_ticket_delete (loop, ticket1);
zloop_ticket_delete (loop, ticket2);
zloop_ticket_delete (loop, ticket3);
//  Check whether loop properly ignores zsys_interrupted flag
//  when asked to
zloop_destroy (&loop);
loop = zloop_new ();
bool timer_event_called = false;
zloop_timer (loop, 1, 1, s_timer_event3, &timer_event_called);
zsys_interrupted = 1;
zloop_start (loop);
//  zloop returns immediately without giving any handler a chance to run
assert (!timer_event_called);
zloop_set_nonstop (loop, true);
zloop_start (loop);
//  zloop runs the handler which will terminate the loop
assert (timer_event_called);
zsys_interrupted = 0;
//  Check if reader removed in timer is not called
zloop_destroy (&loop);
loop = zloop_new ();
bool socket_event_called = false;
zloop_reader (loop, output, s_socket_event1, &socket_event_called);
zloop_timer (loop, 0, 1, s_timer_event5, output);
zstr_send (input, "PING");
zloop_start (loop);
assert (!socket_event_called);
//  cleanup
zloop_destroy (&loop);
assert (loop == NULL);
zsock_destroy (&input);
zsock_destroy (&output);
#if defined (__WINDOWS__)


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


Main web site:

Report bugs to the email <[1]>


Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for 0MQ: 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 LICENSE included with the czmq distribution.


01/17/2021 CZMQ 4.2.1