[repo] Add a publish/subscribe mechanism for inter-instance communication using zmq
Each repo can have a publishing and any number of subscribing sockets
whose addresses are specified in the instance's configuration. An
application or cube can subscribe to some 'topics', and give a callback
that gets called when a message matching that topic is received.
As a proof of concept, this introduces a hook to clean up the caches
associated with the repository when an entity is deleted.
A subscription is added using Repository::zmq::add_subscription;
the callback receives a list representing the received multi-part
message as argument (the first element of the message is its topic).
function datetuple(d) {
return [d.getFullYear(), d.getMonth()+1, d.getDate(),
d.getHours(), d.getMinutes()];
}
function pprint(obj) {
print('{');
for(k in obj) {
print(' ' + k + ' = ' + obj[k]);
}
print('}');
}
function arrayrepr(array) {
return '[' + array.join(', ') + ']';
}
function assertArrayEquals(array1, array2) {
if (array1.length != array2.length) {
throw new crosscheck.AssertionFailure(array1.join(', ') + ' != ' + array2.join(', '));
}
for (var i=0; i<array1.length; i++) {
if (array1[i] != array2[i]) {
throw new crosscheck.AssertionFailure(arrayrepr(array1) + ' and ' + arrayrepr(array2)
+ ' differs at index ' + i);
}
}
}