# CEP 21 - Agent Identification and Discovery¶

CEP: 21 Agent Identification and Distribution 2014-05-05 Robert Carlsen Accepted Standards Track Robert Carlsen

## Abstract¶

Cyclus is designed to have plugin modules that can be easily distributed and installed. A “module” is a shared library containing one or more compiled Cyclus agents. Agents within mouldes must be uniquely identifiable and discoverable by both users managing their Cyclus installation and by the Cyclus kernel itself. A user wishing to use certain modules must install them in a desired location and then identify specific agents in them to Cyclus. This CEP explains where modules can/should be installed and how Cyclus finds and identifies agents in them.

## Agent Spec¶

Agents will be uniquely identified by 3 components together referred to as an “agent spec”:

1. path: e.g. my/module/path

A slash-delimited, valid filesystem path relative to CYCLUS_PATH (see Module Discovery below).

2. library: e.g. MyModule

Name of the compiled shared object library file without the “lib” prefix and without the file extension. If empty, is expanded to the agent class. The example above would correspond to a library file named “libMyModule.so” (linux), “libMyModule.dylib” (darwin), etc.

3. agent class: e.g. MyAgent

The name of the agent’s c++ class as compiled into the shared library file.

An agent spec also has a single-string form composed of the three components separated by colons:

[path]:[library]:[agent-class]

e.g. "my/module/path:MyModule:MyAgent"


Example linux agent specs with corresponding filepath expansions:

my/path:MyModule:MyAgent -> my/path/libMyModule.so
my/path::MyAgent         -> my/path/libMyAgent.so
:MyModule:MyAgent        -> libMyModule.so
::MyAgent                -> libMyAgent.so


## Module Discovery¶

When running a simulation, Cyclus will search the following candidate directories (in order) for each given agent spec:

1. Each colon-separated directory in the CYCLUS_PATH environment variable.
2. The default Cyclus module install directory: [install-dir]/lib/cyclus.

Cyclus will check for the library by building consecutive paths with the following composition:

[candidate-dir]/[path]/lib[library][extension]


Cyclus uses the first matching shared library file found and assumes the specified agent class exists inside it.

## Conventions¶

The path should consist of only alpha-numeric characters, slashes, underscores, and dashes. No spaces. If there are resource files that must be installed with the shared library file, the library and resources should be placed in their own directory.

The shared library name should consist of only alpha-numeric characters, slashes, underscores. No spaces. If the shared library only has a single agent in it, the library should be the same as the agent class. For example, if my agent was named MyAgent, then the library file should be named libMyAgent.so on a linux system. This allows the defaults to prevent stuttering in the agent’s module spec.