[EventGrid] Generate switch expressions instead of dictionary lookups

[danielmarbach]

This PR refactors the SystemEventExtensions.AsSystemEventData method by replacing the existing dictionary-based lookup with a switch expression. This change directly maps event type strings to their corresponding deserialization methods.

While the performance gains are relatively small and mostly noticeable in microbenchmarks or hot-path scenarios, this change streamlines the code and enables the runtime to produce more efficient IL. The overall design remains functionally equivalent, ensuring a smooth transition without breaking existing functionality.

Assumptions

• Performance Improvements: The if statements reduce overhead by eliminating the need for dictionary lookups and indirect delegate calls. This leads to fewer IL-level indirections and leverages direct branch optimizations, which are advantageous in frequently executed code paths.
• Optimized IL Code: The if statements compiles into more predictable branching logic. This allows the JIT compiler to apply inlining and other optimizations more effectively, further enhancing runtime performance.
• Code Clarity and Maintainability: Directly associating event types with their deserialization logic in an if statement improves readability. The intent of the code becomes clearer, making it easier to maintain and less error-prone compared to managing a separate dictionary.

Before

    internal class SystemEventExtensions
    {
        public static object AsSystemEventData(string eventType, JsonElement data)
        {
            if (s_systemEventDeserializers.TryGetValue(eventType, out Func<JsonElement, object> systemDeserializationFunction))
            {
                return systemDeserializationFunction(data);
            }
            else
            {
                return null;
            }
        }

        internal static readonly IReadOnlyDictionary<string, Func<JsonElement, object>> s_systemEventDeserializers = new Dictionary<string, Func<JsonElement, object>>(StringComparer.OrdinalIgnoreCase)
        {
            { SystemEventNames.AcsRecordingFileStatusUpdated, AcsRecordingFileStatusUpdatedEventData.DeserializeAcsRecordingFileStatusUpdatedEventData },
            { SystemEventNames.AcsRouterJobClassificationFailed, AcsRouterJobClassificationFailedEventData.DeserializeAcsRouterJobClassificationFailedEventData },
            ...
        }

After

    internal class SystemEventExtensions
    {
        public static object AsSystemEventData(string eventType, JsonElement data)
        {
            var eventTypeSpan = eventType.AsSpan();
            if (eventTypeSpan.Equals(SystemEventNames.AcsRecordingFileStatusUpdated.AsSpan(), StringComparison.OrdinalIgnoreCase))
                return AcsRecordingFileStatusUpdatedEventData.DeserializeAcsRecordingFileStatusUpdatedEventData(data);
            if (eventTypeSpan.Equals(SystemEventNames.AcsRouterJobClassificationFailed.AsSpan(), StringComparison.OrdinalIgnoreCase))
                ...
            return null;
        }
    }       

[github-actions]

Thank you for your contribution @danielmarbach! We will review the pull request and get back to you soon.

[danielmarbach]

Pinging @m-nash @jsquire @JoshLove-msft @weshaggard since you have reviewed / worked on the previous PR

[azure-sdk]

API change check

API changes are not detected in this pull request.

[JoshLove-msft]

Thanks for the enhancement @danielmarbach! It looks like there are some test failures. Can you please take a look?

[danielmarbach]

@JoshLove-msft I looked at those on my machine on macos and they all passed on Net8 and net9 I can give it another look later

[danielmarbach]

@JoshLove-msft this should work. I missed the ordinal ignore case comparison

[danielmarbach]

@JoshLove-msft in case you are bored ;) #49445