Optimize MessageCracker.IsHandlerMethod for memory

[vasily-balansea]

MessageCracker.IsHandlerMethod is calling MethodInfo.GetParameters() method three times leading to minor memory waste. This is because GetParameters() is allocating a new array when method has parameters. If we cache parameters array then we save a bit of memory and make method a bit faster. IL code is also a bit smaller: 119 bytes vs 127.

Unit tests are passing.

Benchmark results:

| Method | Runtime            | Mean     | Error   | StdDev  | Allocated |
|------- |------------------- |---------:|--------:|--------:|----------:|
| Old    | .NET 8.0           | 194.1 ns | 1.63 ns | 1.44 ns |     480 B |
| New    | .NET 8.0           | 124.3 ns | 0.58 ns | 0.54 ns |     240 B |

| Old    | .NET Framework 4.8 | 518.1 ns | 0.91 ns | 0.76 ns |     481 B |
| New    | .NET Framework 4.8 | 350.0 ns | 1.26 ns | 1.12 ns |     241 B |

Benchmark code:

[SimpleJob(RuntimeMoniker.Net48)]
[SimpleJob(RuntimeMoniker.Net80)]
[MemoryDiagnoser]
[HideColumns("Job", "Gen0")]
public class IsHandlerMethodBenchmark
{
    // UnitTests.MessageCrackerTests.TheseMightBeHandlerMethods
    MethodInfo[] methods = typeof(TheseMightBeHandlerMethods).GetMethods();

    [Benchmark]
    public int Old()
    {
        int count = 0;

        foreach (MethodInfo m in methods)
        {
            if (IsHandlerMethodOld(m))
            {
                count++;
            }
        }

        return count;
    }

    [Benchmark]
    public int New()
    {
        int count = 0;

        foreach (MethodInfo m in methods)
        {
            if (IsHandlerMethodNew(m))
            {
                count++;
            }
        }

        return count;
    }

    private bool IsHandlerMethodOld(MethodInfo m)
    {
        return m.IsPublic
               && m.Name.Equals("OnMessage")
               && m.GetParameters().Length == 2
               && m.GetParameters()[0].ParameterType.IsSubclassOf(typeof(Message))
               && typeof(SessionID).IsAssignableFrom(m.GetParameters()[1].ParameterType)
               && m.ReturnType == typeof(void);
    }

    private bool IsHandlerMethodNew(MethodInfo m)
    {
        ParameterInfo[] parameters;
        return m.IsPublic
                && m.ReturnType == typeof(void)
                && m.Name.Equals("OnMessage")
                && (parameters = m.GetParameters()).Length == 2
                && parameters[0].ParameterType.IsSubclassOf(typeof(Message))
                && typeof(SessionID).IsAssignableFrom(parameters[1].ParameterType);
    }
}

This is obviously a micro optimization since gains (memory and time) are small and unlikely to have any visible effect on application performance. Still I hope you would accept PR.

[CLAassistant]

All committers have signed the CLA.

[gbirchmeier]

It's small, but I like it! You also made it 3 times faster. 😆

FYI, I force-pushed a release-notes update into your branch. (I don't know why I did that instead of a separate commit. I shouldn't do that to other peoples' branches.)

Thanks!