IPGlobalProperties.GetActiveUdpListeners() hangs in .NET 5 preview 2

[martincostello]

Using .NET 5.0.100-preview.2.20176.6, calls to IPGlobalProperties.GetActiveUdpListeners() seem to hang indefinitely.

I can repro this with the following, where the Console output never occurs with .NET 5 preview 2 (the method does not block with .NET Core 3.1).

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
    <RootNamespace>GetActiveUdpListenersHangRepro</RootNamespace>
  </PropertyGroup>
</Project>

using System;
using System.Net.NetworkInformation;

namespace GetActiveUdpListenersHangRepro
{
    internal static class Program
    {
        internal static void Main()
        {
            var properties = IPGlobalProperties.GetIPGlobalProperties();
            properties.GetActiveUdpListeners();

            Console.Write("Press any key to exit...");
            Console.Read();
        }
    }
}

Partial output from dotnet --info:

> dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   5.0.100-preview.2.20176.6
 Commit:    d752c3e07b

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\5.0.100-preview.2.20176.6\

Host (useful for support):
  Version: 5.0.0-preview.2.20160.6
  Commit:  d12f79a4d1

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[martincostello]

Here's a summary of the repro while it's running from Process Explorer:

[martincostello]

Looks like the test for this method isn't run on Windows at all:

runtime/src/libraries/System.Net.NetworkInformation/tests/FunctionalTests/IPGlobalPropertiesTest.cs

Lines 30 to 38 in 110282c

	[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsSubsystemForLinux))] // [ActiveIssue("https://github.com/dotnet/runtime/issues/18258")]
	[PlatformSpecific(TestPlatforms.AnyUnix)]
	public void IPGlobalProperties_AccessAllMethods_NoErrors()
	{
	IPGlobalProperties gp = IPGlobalProperties.GetIPGlobalProperties();
	Assert.NotNull(gp.GetActiveTcpConnections());
	Assert.NotNull(gp.GetActiveTcpListeners());
	Assert.NotNull(gp.GetActiveUdpListeners());

[wfurt]

I could not reproduce it with 5.0 alpha1 but I do see it with preview4 build. So it looks like very recent regression. It is curious as I did not see any recent change in the windows code.