165 Inter-instance communication

   166 ----------------------------

   167 

   168 If your application consists of several instances, you may need some means to

   169 communicate between them.  Cubicweb provides a publish/subscribe mechanism

   170 using ØMQ_.  In order to use it, use

   171 :meth:`~cubicweb.server.cwzmq.ZMQComm.add_subscription` on the

   172 `repo.app_instances_bus` object.  The `callback` will get the message (as a

   173 list).  A message can be sent by calling

   174 :meth:`~cubicweb.server.cwzmq.ZMQComm.publish` on `repo.app_instances_bus`.

   175 The first element of the message is the topic which is used for filtering and

   176 dispatching messages.

   177 

   178 .. _ØMQ: http://www.zeromq.org/

   179 

   180 .. sourcecode:: python

   181 

   182   class FooHook(hook.Hook):

   183       events = ('server_startup',)

   184       __regid__ = 'foo_startup'

   185 

   186       def __call__(self):

   187           def callback(msg):

   188               self.info('received message: %s', ' '.join(msg))

   189           self.repo.app_instances_bus.subscribe('hello', callback)

   190 

   191 .. sourcecode:: python

   192 

   193   def do_foo(self):

   194       actually_do_foo()

   195       self._cw.repo.app_instances_bus.publish(['hello', 'world'])

   196 

   197 The `zmq-address-pub` configuration variable contains the address used

   198 by the instance for sending messages, e.g. `tcp://*:1234`.  The

   199 `zmq-address-sub` variable contains a comma-separated list of addresses

   200 to listen on, e.g. `tcp://localhost:1234, tcp://192.168.1.1:2345`.

   201 

   202