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Created March 26, 2013 18:51
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// The Meerkat Pattern
// In which we address the slow subscriber problem by asking for
// a show of hands before we start publishing.
#include "czmq.h"
static void
publisher_task (void *args, zctx_t *ctx, void *pipe)
zctx_set_linger (ctx, 1000);
void *publisher = zsocket_new (ctx, ZMQ_XPUB);
zsocket_set_xpub_verbose (publisher, 1);
zsocket_bind (publisher, "tcp://*:6001");
// Calling thread tells us the population size
char *population = zstr_recv (pipe);
int still_waiting = atoi (population);
byte meerkat [] = { 1, 'M', 'e', 'e', 'r', 'k', 'a', 't' };
while (still_waiting) {
zframe_t *frame = zframe_recv (publisher);
if (!frame)
break; // Interrupted
if (zframe_size (frame) == sizeof (meerkat)
&& memcmp (zframe_data (frame), meerkat, sizeof (meerkat)) == 0)
// Dump the frame contents for the benefit of the reader
zframe_print (frame, NULL);
zframe_destroy (&frame);
// Now broadcast our message
zstr_send (publisher, "Hello, World!");
zclock_sleep (250);
zstr_send (pipe, "DONE");
// .split subscriber task
// The subscriber sends a "Meerkat" subscription and then
// any other subscriptions it wants:
static void
subscriber_task (void *args, zctx_t *ctx, void *pipe)
void *subscriber = zsocket_new (ctx, ZMQ_XSUB);
zsocket_connect (subscriber, "tcp://localhost:6001");
// Tell publisher we're here
byte meerkat [] = { 1, 'M', 'e', 'e', 'r', 'k', 'a', 't' };
zmq_send (subscriber, &meerkat, sizeof (meerkat), 0);
// Subscribe to everything as well (empty subscription)
zmq_send (subscriber, &meerkat, 1, 0);
char *hello = zstr_recv (subscriber);
puts (hello);
free (hello);
// .split main task
// The main task starts publisher task and then the subscribers:
int main (void)
zctx_t *ctx = zctx_new ();
// Size of target population
srand ((unsigned) time (NULL));
int population = randof (10) + 1;
// Start publisher task
void *pipe = zthread_fork (ctx, publisher_task, NULL);
zstr_send (pipe, "%d", population);
// Start target population
while (population--)
zthread_fork (ctx, subscriber_task, NULL);
// Wait for publisher to complete
free (zstr_recv (pipe));
zctx_destroy (&ctx);
return 0;
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