Two features of open625451 enable realtime Pubsub: The custom state machine for PubSub-Components and the generation of offset tables for the PubSub NetworkMessage. Both features are showcased in the respective examples for Publishers and Subscribers.

Custom State Machine

The custom state machine mechanism lets user-defined code control the state of the PubSub-Components (PubSubConnection, ReaderGroup, Reader, ...). Hence the user-defined code is also responsible to register time-based events, network connections, and so on.

This allows the integration with non-POSIX networking APIs for publishers and subscribers. Note that the provided examples are still POSIX based, but handle all sockets in userland.

NetworkMessage Offset Table

Typically realtime PubSub is used together with the periodic-fixed header layout where the position of the content in the NetworkMessage does not change between publish cycles. Then the NetworkMessage offset tables can be generated to speed up the updating and parsing of NetworkMessages. For the relevant fields, the well-known offsets are computed ahead of time. Each offset furthermore has a known source (the NodeId of the respective PubSub-Component in the information model).

The NetworkMessage offset table is usually generated when the ReaderGroup/WriterGroup changes its state to OPERATIONAL. At this time, from the offset table, each field of the NetworkMessage is resolved to point to a backend information source with fast access. Then the updating/parsing of the NetworkMessage in the publish interval is simply a matter of looping over the offset table and performing mostly memcpy steps.