Presently the components of OpenVisualizer operate within a single process. We wish to experiment with extending this operation across processes and machines, as shown in the diagram below.
Messaging
Presently we implement EventBus messaging with PyDispatch, which provides communication between threads in a single process.
Between Processes
On an embedded LBR, we plan to use the native POSIX message queue due to its built-in availability. The posix_ipc module for Python provides access to this functionality.
Remote GUI host and LBR
We wish to minimize the processing required by the LBR due to its limited resources, particularly for a sub-Linux implementation. Therefore, the LBR pushes information to the Remote GUI. However, the GUI also may signal to the LBR, for example to toggle DAGroot status.
WebSockets (RFC 6455) supports our proposed bi-directional messaging protocol, and as a standard, supports OpenWSN's goals.
Tools
| Role | Tool | Notes |
|---|---|---|
| WebSocket client | websocket-client | Installed with pip. |
Other Implementations
Nanomsg and ZeroMQ provides a common messaging API for a variety of endpoints – threads, processes, and machines. They are open source, but not standards. However, it would be efficient to use a single tool for messaging across all domains.
Nanomsg is developed by Martin Sústrik, the original author of ZeroMQ. Sústrik left ZeroMQ due to a dispute over trademarks, as described in a Linux Weekly News article.
Celery provides a distributed message queue, but is more heavy-duty and requires a message broker.