I have a Pyro4 distributed system with multiple clients connecting to a single server. These clients connect to a remote object, and that object may allocate some resources in the system (virtual devices, in my case).
Once a client disconnects (let's say because of a crash), I need to release those resources. What is the proper way to detect that an specific client has disconnected from an specific object?
I've tried different things:
Daemon.clientDisconnected method. I get a connection parameter from this method. But I can't correlate that to an object, because I have no access to which remote object that connection refers to.Pyro4.current_context in Daemon.clientDisconnected. This doesn't work because that is a thread-local object. That in place, if I have more clients connected than threads in my pool, I get repeated contexts.Proxy._pyroAnnotations as in the "usersession" example available by the Pyro4 project, doesn't help me, because again, I get the annotation from the Pyro4.core.current_context.annotations attribute, which shows me wrong annotations when Daemon.clientDisconnected is called (I imagine due to a thread related issues).instance_mode="session" and the __del__ method in the remote class (as each client would have a separate instance of the class, so the instance is supposed to be destroyed once the client disconnects). But this relies on the __del__ method, which has some problems as some Python programmers would point out.I added my current solution as an answer, but I really would like to know if there's a more elegant way of doing this with Pyro4, as this scenario is a recurrent pattern in network programming.
Pyro 4.63 will probably have some built-in support for this to make it easier to do. You can read about it here http://pyro4.readthedocs.io/en/latest/tipstricks.html#automatically-freeing-resources-when-client-connection-gets-closed and try it out if you clone the current master from Github. Maybe you can take a look and see if that would make your use case simpler?