Implement threading

[minecrawler]

Browsers can use WebWorkers and NodJS can use a Cluster.

Ideas:

• cache all data and logic in the workers, however that would mean that all components have to be synchronized after every batch of systems is finished
• upload the whole world to every worker whenever it is run, while simple it means a lot of overhead

[minecrawler]

Better: set up a worker per system and use the communication channel to sync the data set. Then execute the workers per execution group in the execution pipeline, so that everything inside a group is truely executed in parallel.

Which still asks for a way to sync the components :/

I also wonder how efficient syncing would be, especially for worlds where the groups are small, but there is plenty of data to sync.

[minecrawler]

I think, since 2020Q2 a lo happened and with v0.5.0, a lot of things are in place to come up with a more concrete plan.

• (generic, automated) serialization support is in place
• sync-points aid with synchronization and proper schedule planning
• Bevy released its "Extraction" points architecture in 0.6, which feels doable with sim-ecs 0.5.0 (and better support comes in 0.5.1)

What's left is to create an API for scheduling and syncing multiple worlds easily and still have a certain degree of determinism and overview. Spawning of threads (service workers or process-clusters) should be under the hood, just for the extra comfort!