Spawn jobs from within other jobs

[optimise]

I would like official to make it possible to spawn jobs from within other jobs for job system in future editor engine release. This will enable much more possibilities but also to address the main thread job stalling issue at dots physics that can’t be solved without this job system improvement as following:

If you are referring to the Job.Complete() call we can see in my comment here, this one is currently necessary because the solver does not know yet how many jobs to spawn while the phasing algorithm is still operating, which decides how many parallel phases there will be.
In a previous version, this Job.Complete() call was not present, which caused the solver to spawn as many jobs as there could be maximally required, which was way too much and overwhelmed the job system with unnecessary job schedules and executions (max “solver iteration” times “32 phases” many job executions), which in the end effectively slowed the physics pipeline down significantly. This is no longer the case.

Ideally, we would launch a solver job that then launches the correct amount of solver phase jobs once the information comes in, freeing up the main thread. However, since in the C# job system there is currently no way to spawn jobs from within other jobs, this is not something that we can do at the moment.
We do have an eye on that though as a general area of improvement.

[JohnPontoco]

I would also like to +1 this feature, although I recognize that it’s not very likely. There’s an old manual page on why they don’t allow this:
https://docs.unity3d.com/Packages/com.unity.jobs@0.51/manual/scheduling_a_job_from_a_job.html

But hopefully this could be revisited, or allowed with an ‘unsafe’ designator?

[kevinmv]

Copied from my response on Discord:

We have some internal plans on exploring this area, however there is no timeline for it since there is a bunch of care to be taken when allowing for the current level of job safety we provide and allowing jobs to schedule jobs. It’s not impossible and is something we want to add as you are correct there are lots of potential benefits, however if you’re not careful we can enter a deadlocking, unsafe, non-deterministic disaster which we want to ensure we don’t provide