Add RegexOptions.Compiled option to RegexRouteConstraint

[eugeneogongo]

Add RegexOptions.Compiled option to RegexRouteConstraint

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Summary of the changes (Less than 80 chars)

Description

Add RegexOptions.Compiled option to RegexRouteConstraint

Fixes #46154

[ghost]

Thanks for your PR, @eugeneogongo. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[eugeneogongo]

@surayya-MS would you go through this PR?
Thank you.

[danmoseley]

thanks

[mkArtakMSFT]

@surayya-MS can you please review this? Thanks!

[mkArtakMSFT]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[surayya-MS]

Thanks for the contribution

[JamesNK]

I looked back in time, and we've never used RegexOptions.Compiled. Not even from the first commit:

aspnetcore/src/Microsoft.AspNet.Routing/RegexConstraint.cs

Line 18 in a917cbd

Constraint = new Regex(regexPattern, RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);

Maybe Compiled was left out accidentally, but it could have been purposefully removed. I worry about web app startup time. For example, an app could have thousands of routes with regex constraints. Are they all compiled when the app starts up? That could really hurt time to first request.

Edit: I'm going to reopen #46154. Make sure we aren't helping one area by hurting another.

[eugeneogongo]

@JamesNK The cost of constructing the Regex object may be higher, but the cost of performing matches with it is likely to be much smaller.

[ghost]

Hi @eugeneogongo. It looks like you just commented on a closed PR. The team will most probably miss it. If you'd like to bring something important up to their attention, consider filing a new issue and add enough details to build context.

[JamesNK]

@eugeneogongo The performance improvement in matching the constraint is great, but I think we should take some time to verify that nothing else (startup time, total app memory usage) has regressed when there are a lot of routes with regex constraints.

If measuring highlights RegexOptions.Compiled is a problem, there might be ways to have the best of both worlds. For example, waiting to create the Regex instance until the first time the route constraint is evaluated.