Monitoring a couchbase bucket with libevent - c

Question

I'm trying to implement a C application that will monitor writes / modifications / new documents events happening on a couchbase remote cluster coming from a different application. I am now familiar with couchbase C SDK and synchronous instances but I have trouble combining it with libevent for asynchronous I/O.
I read couchbase libevent plugin documentation and the external event loop integration example but I cannot grasp how I would tell my event_base that, for instance:
Monitor this file on this bucket and send me a callback when it's modified
Here's what I do so far:
Firstly, I create my libevent IO option
struct event_base *mEvbase = event_base_new();
lcb_t instance;
lcb_error_t err;
struct lcb_create_io_ops_st ciops;
lcb_io_opt_t ioops;
memset(&ciops, 0, sizeof(ciops));
ciops.v.v0.type = LCB_IO_OPS_LIBEVENT;
ciops.v.v0.cookie = mEvbase;
err = lcb_create_libevent_io_opts(0, &ioops, mEvbase);
if (err != LCB_SUCCESS) {
ERRORMSG0("Failed to create an IOOPS structure for libevent: %s\n", lcb_strerror(NULL, error));
}
and then I create my instance:
struct lcb_create_st create_options;
std::string host = std::string("couchbase://192.168.130.10/");
host.append(bucket);
const char password[] = "password";
create_options.version = 3;
create_options.v.v3.connstr = host.c_str();
create_options.v.v3.passwd = password;
create_options.v.v3.io = ioops;
//Creating a lcb instance
err = lcb_create(&instance, &create_options);
if (err != LCB_SUCCESS) {
die(NULL, "Couldn't create couchbase handler\n", err);
return;
}
/* Assign the handlers to be called for the operation types */
lcb_set_bootstrap_callback(instance, bootstrap_callback);
lcb_set_get_callback(instance, generic_get_callback);
lcb_set_store_callback(instance, generic_store_callback);
and then I schedule a connection.
//We now schedule a connection to the server
err = lcb_connect(instance);
if (err != LCB_SUCCESS) {
die(instance, "Couldn't schedule connection\n", err);
lcb_destroy(instance);
}
lcb_set_cookie(instance, mEvbase);
I use libcouchbase version 2.0.17, libevent core version 2.0.so.5.1.9 and libevent extra version 2.0.so.5.1.9. With the code above, my instance cannot connect to couchbase. I get the following warnings:
event_pending: event has no event_base set.
event_add: event has no event_base set.
So two problems here: I can't connect using the above code and I don't know which direction to go to start receiving events. If anyone point me towards a link or a coded example of this simple case that would unblock me.

Answer 1

Ensure that you are using the same libevent version for both the library and your application. Installing the packages from the repository, you will need to align with the libevent version used therein (e.g. ldd /usr/lib64/libcouchbase_libevent.so). Keep in mind that this must be of the same ABI (so for example, using libevent's 2.0 -> 1.4 compat layer will not work, as the two versions contain different ABIs, and using a libcouchbase_libevent.so linked against 1.4 will break under 2.0).
For the full exchange, see the the comments on the question :)