feat(dot/parachain): create worker pool for PVF host

[edwardmack]

Changes

This creates a PVF host which will be called for candidate validation. It enables the use of a worker pool that will contain workers that will preform the candidate validation task.

• The candidate validation subsystem creates and starts an instance of the PVF Host.
• The PVF host contains a pool of candidate validation workers (one for each of the validation code instances)
• The candidate validation subsystem calls the Validate method of the PVF host to validate candidates as needed.
• The PVF host initializes validation workers when needed

Tests

go test github.com/ChainSafe/gossamer/dot/parachain/candidate-validation

Issues

closes #3934

[EclesioMeloJunior]

Hey @edwardmack could you explain how the candidate validation workers are instantiated? what is the logic to start a new worker?

[edwardmack]

Hey @edwardmack could you explain how the candidate validation workers are instantiated? what is the logic to start a new worker?

Hi @EclesioMeloJunior when a call to host.Validate is made the validate function calls poolContainsWorker to determine if there is a worker with the given code hash, if not, then one is created by calling workerPool.newValidationWorker.

[kishansagathiya]

You can put more comments explaining code, that would help us understand the code and design better while reviewing.

[EclesioMeloJunior]

LGTM! Great work Ed 🚀

[axaysagathiya]

I have reviewed a few files and made some comments. I will look into other files later.

[edwardmack]

@kishansagathiya and @axaysagathiya, I think I've addressed all comments, so they can be resolved, and this is ready for a re-review. If you still find changes that need to be done before approval please let me know.

[kishansagathiya]

🎉
I have some small comments. Approving to avoid one more iteration. So, you can resolve those yourself and merge this PR.

[kishansagathiya]

All the concurrency related code has been removed from this PR. So, this is basically same as previously in terms of behaviour but the code has been moved around.

If we were to merge this we need to have a separate issue to actually put concurrency in this an make pvf host functional.

I want to get a nod from @timwu20 and @EclesioMeloJunior on whether you are okay to merge this in. I am asking because I am bit confused on this.

[edwardmack]

If we were to merge this we need to have a separate issue to actually put concurrency in this an make pvf host functional.

Issue #4185 has been created to track this issue.