fixes https://github.com/TryGhost/Toolbox/issues/370
- we no longer need `bthreads` because we can use native
`worker_threads` now we don't have to support Node 10 any longer
- this allows us to clean up a dependency and stick with native
libraries
- the referenced node-sqlite3 issue should be fixed (or at least, we now
maintain it so we can fix it if not)
no issue
- When jobs are performing CPU intensive tasks they block main process'
event loop. They also can cause memory leaks or unexpected crashes
effectively crashing the parent proccess. To address these issues jobs need to be performed off of main
process. Worker Threads (https://nodejs.org/dist/latest-v12.x/docs/api/worker_threads.html)
are the best candidate for such work.
- These changes introduce an integration on top of bree
(https://github.com/breejs/bree/) which allows to run recurring
jobs in worker thereads. It falls back to child process execution for
Node v10 running without `--experimental-worker` flag.
- bree was chosen not only because it gives a polyfill for older Node
versions. It has support for some of the future use-cases Ghost is looking to
implement, like scheduled jobs.
- This changeset also includes a complete example of job running on an
interval with a possibility for graceful shutdown
