# objectloader2 for the Speckle viewer

This is an updated object loader for the Speckle viewer rewritten in Typescript.

The main aim for the objectloader is:

- download Speckle objects as JSON
- cache in IndexedDB so the same objects aren't downloaded twice
- give data to the viewer, as returned by the `getObjectIterator` generator, as soon as possible
- do the above as concurrently as a browser allows

## Architecture

To achieve increased concurrency, the different phases of the objectloader are divided into pools of workers with queues to feed them.

```mermaid
flowchart TD
  start(Root Commit)
  getIds(Parse Root to get all IDs)
  cached{Cached?}
  download(Download IDs)
  save(Write to Cache)
  load(Load from Cache)
  generate(Generate to Viewer!)

  start --> getIds
  getIds --> cached
  cached -->|Yes| load
  cached -->|No| download
  load --> generate
  download --> generate
  download --> save

```

From the list of IDs, they are moved to a queue to be begin checking the cache from a pool of readers.

Results are then sent to the viewer, if found, else they're send to the download queue.

The download queue is a batching mechanism that gets what is available, up to a limit or a timeout. The results are parsed and given to the generator and written to another queue.

The write cache queue is processed with a single writer to the indexeddb.