FAQ¶

Q: Who develops n3rv ?¶

A: My name is Clément Gamé and i am the main and only developper of n3rv framework.

Q: I did a useful code modification , can i send it ?¶

A: Yes, feel free to send a pull request on the main n3rv code repository, on github.

Q: How can i contact the developper ?¶

A: You can contact me by mail at clement.game[__at__]gmail.com, or via twitter (@WintermeW)

Q: What happens when a service controller goes down ?¶

A: Not much actually, you running nodes will keep going as if nothing happened. The only problem is that new nodes and node bindings won’t be able to register, therefore the other nodes will not be aware of them.

Q: Can i attach multiple receive callbacks to a single ZMQ socket ?¶

A: No, you can’t. If you call service::attach() more than once on the same qhandler*, the last attached callback will win! But you can break your message processing logics into multiple functions that your single callback will call conditionally.

Q: Inversly, can i attach the same callback on multiple sockets ?¶

A: Yes you can, no problem. You can even have a single receive callback for all your sockets, but that would be poor design.

Q: In many cases, ZeroMQ allows a single socket to connect to multiple endpoints. Can i do that with n3rv ?¶

A: Yes you can ! n3rv::service::connect() has a qhandler* ref overloading, which means you can use it to connect multiple times with the same handler (& incidentally zeroMQ socket) reference.

Q: Can i use multiple service controllers inside a n3rv cluster, for redundency purpose ?¶

A: Well, yes and no..You can perfectly instanciate multiple service controllers on the same network and subscribe some nodes on all of them, but as we speak a given node can’t connect to multiple service controllers at the same time and use indiferently one or the other (by the usual means at least).

Q: Given that a node’s service_class is always named after its implemented C++ class name, why do we have to set it manually in uid ?¶

A: Mainly because of C++’s lack of reflection capacities, and because:

• typeid(this) return value is dependant of the compiler’s implementation (g++ for instance returns the mangled class name)
• typeid(this) does not see inheritence and returns the object’s parent class.

Q: Why do n3rv receive callbacks have to be static methods ?¶

A: Again this is due to a language limitation. At compile time, the signature of a non static method changes (mangling, this pointer adding,..), this is why they can’t be used as callbacks. The only way to go is to declare a static method and pass the calling object pointer as a void*, casting it back in its true type later in the callback.

Q: why do most of your object-returning functions don’t return refs ?¶

A: Copy elision, baby ! ;)

Q: Why is the n3rv library not released as a “headers only” source, as most of the other C++ libs do nowadays ?¶

A: Good question, i just thought that since multiple library linkings are necessary in order to use n3rv, one more wouldn’t make much difference.