einaros / dynobot

The dynobot experiment

Goal

Host an EventEmitter like object with an additional API in a server process, and let a client process make calls against a proxy of it - as if it all happened in the client process. The fact that an object in another process is actually used should be completely transparent.

What can this be used for

An example of its use would be in an IRC bot. By exposing an identical proxy object in a client process, the server process can stay up (and connected to an IRC server) indefinitely, while a client process spawns, does some stuff and shuts back down. Whenever the client shuts down, all traces of it should be removed.

The same should apply for other EventEmitter like scenarios, such as HTTP handler processes be plugged and removed at will, while the actual HTTP server stays up all along.

How it works right now

This application will proxy function calls from a client process to a server server process.

Arguments of type function will be replaced with tokens, which allow the server to establish new callbacks on the server side. When these callbacks are called, the server will send a message back to the client - including the token - which enables the client to fire its intended callback. Effectively, cross-process calls and callbacks work.

Furthermore, event handlers can be registered by the client, and have them transparently be added on the server instead. These will work like the callbacks described above. Running someProxy.on('event', function(arg) { console.log(arg); }); will cause the server to pass notifications back whenever event is raised on the proxied object.

In order to avoid leaking resources on the client side, weak references are used on the server. When a callback is no longer required, a situation which is left up to the garbage collector to detect, a message is passed to the client instructing it to release all handles to the callback. Should the client side of the callback as a result of this no longer be referenced by anything, it too will be garbage collected.

Next, to also enable the client to do something like:

function handler() {}
proxyObject.on('foo', handler);
proxyObject.removeListener('foo', handler);

.. and consequently have the server garbage collect its side of the handler callback, references to the same function is detected on the client side, and an existing callback id will be passed, rather than a new one being created.

Finally, when a client disconnects, the server will attempt to automatically remove all EventEmitter-like handlers it has attached. This is done by taking note of all calls to on type functions, and passing them all to removeListener after the client has disconnected.

See also

Notes in child.js.

Todos

• Track function arguments passed recursively in arguments - from both sides.
• Write tests (rather than the current manual verification) of the relayed garbage collection info in effect.