RegexOptions.Compiled impacts Android startup

[jonathanpeppers]

Description

Reviewing a customer issue, we noticed usage of RegexOptions.Compiled impacts startup quite a bit:

This was coming from the AppCenter SDK in the customer's app:

https://github.com/microsoft/appcenter-sdk-dotnet/blob/b19ec99e16e554eb1382342b2852b16f7d8f0084/SDK/AppCenter/Microsoft.AppCenter.Shared/AppCenter.cs#L26

This shows up as a regression from Xamarin.Android -> .NET 6, because RegexOptions.Compiled was not implemented at all in mono/mono.

The question here, is how do we get the previous behavior from mono/mono? Is there a way to toggle RuntimeFeature.IsDynamicCodeCompiled?

runtime/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.cs

Line 105 in 807d091

if (RuntimeFeature.IsDynamicCodeCompiled && (options & RegexOptions.Compiled) != 0)

If there is a way to toggle RuntimeFeature.IsDynamicCodeCompiled, should we consider turning on this flag by default on Android? I've found System.Reflection.Emit to be very impactful to startup.

Reproduction Steps

1. dotnet new android
2. Open MainActivity.cs and put _ = new Regex(@"([^;=]+)=([^;]+)(?:;\s*)?", RegexOptions.Compiled); in the OnCreate() method.
3. Build/run with dotnet build -c Release -t:Run

Expected behavior

RegexOptions.Compiled doesn't have a significant impact to Android startup. (Or we have a feature flag to turn it off)

Actual behavior

RegexOptions.Compiled has a significant impact to Android startup.

Regression?

From a customer's perspective they might say this is startup performance regression from Xamarin.Android to .NET 6.

Known Workarounds

Don't use RegexOptions.Compiled, use Normal.

Configuration

I tested this with the .NET 6.0.400-preview.22301.10 SDK, and the SR 1 version of .NET MAUI.

Other information

dotnet trace output: regexoptions.compiled.zip

Tagging subscribers to this area: @dotnet/area-system-text-regularexpressions
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

Reviewing a customer issue, we noticed usage of RegexOptions.Compiled impacts startup quite a bit:

This was coming from the AppCenter SDK:

https://github.com/microsoft/appcenter-sdk-dotnet/blob/b19ec99e16e554eb1382342b2852b16f7d8f0084/SDK/AppCenter/Microsoft.AppCenter.Shared/AppCenter.cs#L26

This shows up as a regression from Xamarin.Android -> .NET 6, because RegexOptions.Compiled was not implemented at all in mono/mono.

The question here, is how do we get the previous behavior from mono/mono? Is there a way to toggle RuntimeFeature.IsDynamicCodeCompiled?

runtime/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.cs

Line 105 in 807d091

if (RuntimeFeature.IsDynamicCodeCompiled && (options & RegexOptions.Compiled) != 0)

If there is a way to toggle RuntimeFeature.IsDynamicCodeCompiled, should we consider turning on this flag by default on Android? I've found System.Reflection.Emit to be very impactful to startup.

Reproduction Steps

1. dotnet new android
2. Open MainActivity.cs and put _ = new Regex(@"([^;=]+)=([^;]+)(?:;\s*)?", RegexOptions.Compiled); in the OnCreate() method.
3. Build/run with dotnet build -c Release -t:Run

Expected behavior

RegexOptions.Compiled don'ts have a significant impact to Android startup. (Or we have a feature flag to turn it off)

Actual behavior

RegexOptions.Compiled has a significant impact to Android startup.

Regression?

From a customer's perspective they might say this is startup performance regression from Xamarin.Android to .NET 6.

Known Workarounds

Don't use RegexOptions.Compiled, use Normal.

Configuration

I tested this with the .NET 6.0.400-preview.22301.10 SDK, and the SR 1 version of .NET MAUI.

Other information

dotnet trace output: regexoptions.compiled.zip

Author:	jonathanpeppers
Assignees:	-
Labels:	area-System.Text.RegularExpressions
Milestone:	-

[stephentoub]

RegexOptions.Compiled is a tradeoff between startup overhead and throughput: it adds overhead to constructing the Regex in exchange for making regexes execute faster. Are you seeing this construction cost increase but throughput not also increase? If they both go up, then the opt-in flag is doing what it's supposed to do, and if a customer doesn't want to tradeoff that construction overhead for throughput, they shouldn't be setting Compiled to opt-in. (And if they want both, they should consider using the regex source generator in .NET 7 instead; this will give them both the construction perf and the throughput perf, at the expense of a bit larger IL size.)

[jonathanpeppers]

In this case, the customer's use of RegexOptions.Compiled was coming from a NuGet owned by Microsoft. I was curious if there is some way to opt out of RuntimeFeature.IsDynamicCodeCompiled? Or some way to get back to the behavior they had from Xamarin.Android (mono/mono)?

[danmoseley]

Just curious, why do they not pass it when targeting .NET Standard?

#if NETSTANDARD
        static readonly Regex _secretsRegex = new Regex(SecretsPattern);
#else
        static readonly Regex _secretsRegex = new Regex(SecretsPattern, RegexOptions.Compiled);
#endif

[jonathanpeppers]

If you look at blame, it doesn't actually give much detail:

microsoft/appcenter-sdk-dotnet@70f7944

I'm not sure what issue they're trying to solve here either. It seems like the old code would have worked in Xamarin.Android in 2019 to me?

[danmoseley]

My guess is that they thought it was still broken. I think the to-do here is to just pass on Stephen's guidance. Startup time, throughput, on disk size - pick two!

If there is a way to toggle RuntimeFeature.IsDynamicCodeCompiled, should we consider turning on this flag by default on Android? I've found System.Reflection.Emit to be very impactful to startup.

Question for @steveisok I think.

[jonathanpeppers]

On Android, we would pretty much never want throughput for anything. So that is why the default setting might be interesting.

Tagging subscribers to 'arch-android': @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

Reviewing a customer issue, we noticed usage of RegexOptions.Compiled impacts startup quite a bit:

This was coming from the AppCenter SDK in the customer's app:

https://github.com/microsoft/appcenter-sdk-dotnet/blob/b19ec99e16e554eb1382342b2852b16f7d8f0084/SDK/AppCenter/Microsoft.AppCenter.Shared/AppCenter.cs#L26

This shows up as a regression from Xamarin.Android -> .NET 6, because RegexOptions.Compiled was not implemented at all in mono/mono.

The question here, is how do we get the previous behavior from mono/mono? Is there a way to toggle RuntimeFeature.IsDynamicCodeCompiled?

runtime/src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/Regex.cs

Line 105 in 807d091

if (RuntimeFeature.IsDynamicCodeCompiled && (options & RegexOptions.Compiled) != 0)

If there is a way to toggle RuntimeFeature.IsDynamicCodeCompiled, should we consider turning on this flag by default on Android? I've found System.Reflection.Emit to be very impactful to startup.

Reproduction Steps

1. dotnet new android
2. Open MainActivity.cs and put _ = new Regex(@"([^;=]+)=([^;]+)(?:;\s*)?", RegexOptions.Compiled); in the OnCreate() method.
3. Build/run with dotnet build -c Release -t:Run

Expected behavior

RegexOptions.Compiled doesn't have a significant impact to Android startup. (Or we have a feature flag to turn it off)

Actual behavior

RegexOptions.Compiled has a significant impact to Android startup.

Regression?

From a customer's perspective they might say this is startup performance regression from Xamarin.Android to .NET 6.

Known Workarounds

Don't use RegexOptions.Compiled, use Normal.

Configuration

I tested this with the .NET 6.0.400-preview.22301.10 SDK, and the SR 1 version of .NET MAUI.

Other information

dotnet trace output: regexoptions.compiled.zip

Author:	jonathanpeppers
Assignees:	-
Labels:	area-System.Text.RegularExpressions, os-android, untriaged
Milestone:	-

[steveisok]

If we were to do anything, I think it would have to be through a runtime feature switch. @jonathanpeppers, how significant are we talking vs what was in mono/mono?

[teo-tsirpanis]

Just curious, why do they not pass it when targeting .NET Standard?

@danmoseley they are targeting .NET Standard 1.0 only, which does not have Compiled.

https://github.com/microsoft/appcenter-sdk-dotnet/blob/b19ec99e16e554eb1382342b2852b16f7d8f0084/SDK/AppCenter/Microsoft.AppCenter/Microsoft.AppCenter.csproj#L6