Improve the no-op hashing performance

[nkolev92]

Currently the no-op hash is calculated by creating a json string of the dependency graph spec for said project.
This involves a lot of duplicate + using jsonwriter for hash is not ideal.

This issue tracks the investigation for improving that hashing performance.

I discussed with @cristinamanum and @zivkan

The suggestion is move to a normal hashing function instead of using the package specwriter.
The challenge is that we don't know if the package spec is mutated during restore.

Given that here are the options.

• Consider setting a Locked property, to disable mutation after a certain point.
• Use an intermediate class that can generate the hashcode on demand (this will require coordination to ensure the hash generation is synchronized).
• Restore Runner before invoking the restore command can prepopulate the hash code for all the package specs.

This is expected to be a long investigation, because while perf is one goal, we need to ensure this doesn't get regressed in the future.

I did prototype these changes and it showed a significant improvement for large slns with deep project graphs, up to 2-4x faster hash generation. The hash generation right now is about ~30% of the time spent in the restore part (not dg spec generation).

So cmd could see numbers like 7s to 6.8s, but VS will relatively better perf, example, 1.1s -> 900ms.

[nkolev92]

Setting the estimate to 30-ish, but likely I will only spend 5 on it in S177.

[nkolev92]

Moving to S178.

[nkolev92]

deprioritizing for now.

[KirillOsenkov]

I've done research on string hashing for MSBuild and we settled on a very decent hash function:
https://github.com/KirillOsenkov/MSBuildStructuredLog/wiki/String-Hashing

This is what MSBuild uses for string hashing:
https://github.com/dotnet/msbuild/blob/8da5fc70969354a2849e4dcec20cf59b98f4d2c3/src/Build/Logging/BinaryLogger/BuildEventArgsWriter.cs#L1319

It's also combineable:
https://github.com/dotnet/msbuild/blob/8da5fc70969354a2849e4dcec20cf59b98f4d2c3/src/Build/Logging/BinaryLogger/BuildEventArgsWriter.cs#L1335

[KirillOsenkov]

I'd love to see this prioritized because it does seem like we could speed up restore significantly.

[nkolev92]

In this branch, I'm caching the hash generation for the package spec https://github.com/NuGet/NuGet.Client/compare/dev-nkolev92-storePackageSpecHashes.

There's another change for the algorithm itself: NuGet/NuGet.Client#5655.

[KirillOsenkov]

@jeffkl

[nkolev92]

I rebased my branch to get NuGet/NuGet.Client@89f1251.

I'll probably need @jeffkl or @GenelleM to rerun the no-op tests with my change to see how much of a dent they're making.