Threadpool autorelease

[jkoritzinsky]

Implement feature switch to set up NSAutoreleasePools on threadpool threads for each job dispatch.

[jkoritzinsky]

Timeouts are #47850

Can I get another review pass.

@eerhardt can you validate that I set up the feature switch correctly?

[eerhardt]

I think this needs to be the other way. false is the default in the code. The feature switch is usually the opposite of the default. See GlobalizationMode.Invariant above. The default in the code is false and setting the feature switch to true trims away ICU dependencies.

Which value for this setting trims code? true or false?

[jkoritzinsky]

Setting this switch to false (which is the default in code) should trim out the call to DispatchItemWithAutoreleasePool.

[eerhardt]

Ok. Just know that the code won't be trimmed unless someone explicitly sets the switch.

[eerhardt]

I think the feature switch is now set up correctly.

I'm wondering how much code is actually going to be trimmed. It looks like only the ThreadPoolWorkQueue.DispatchItemWithAutoreleasePool static method, and 2 extern methods will be able to be trimmed. I still question if this is worth the effort of defining and maintaining a feature switch here.

[jkoritzinsky]

The thread pool's performance is very sensitive to inlining and branching decisions. By enabling trimming here, we can make some of these branches disappear and eek out a little more performance. This one isn't particularly focused on size reduction.

[eerhardt]

This is a partial class. Isn't there a file where you can put this property so it doesn't need to be duplicated?

[jkoritzinsky]

There actually isn't. ThreadPool.cs didn't actually have the ThreadPool type and I don't want to make a new ThreadPool.cs in the same PR where I'm renaming the old one because once it's squashed, the git history will get all messed up.

[jkotas]

Can we put it in ThreadPoolWorkQueue.AutoreleasePool.OSX.cs?

public static partial class ThreadPool
{
    internal static bool EnableDispatchAutoreleasePool { get; } = AppContextConfigHelper.GetBooleanConfig("System.Threading.ThreadPool.EnableDispatchAutoreleasePool", false);
}

I understand that it is a minor violation of coding conventions, but I think it is acceptable.

Also, we won't be unnecessarily reading the property on non-OSX platforms anymore.

[jkoritzinsky]

Done!

[jkoritzinsky]

Anyone have any more feedback here before we merge this in?

[AaronRobinsonMSFT]

@jkoritzinsky I think @stephentoub's request at #47592 (comment) is the only outstanding question I have.

[jkoritzinsky]

Ok. Should I just run the benchmarks locally or is there a way I can run them on the benchmark lab machines for more reliable comparisons? Given that this is the threadpool and the possible perf change is extremely small, I don't know if I trust my personal machine to give stable enough results.

[jkoritzinsky]

iOS test run didn't time out on the second run, so I'll merge this in.