Add additional TFM's to package

build/scripts/Targets.fs

@@ -119,7 +119,7 @@ let private generateApiChanges _ =
                 "assembly-differ"
                 $"previous-nuget|%s{p}|%s{currentVersion}|%s{tfm}";
                 //$"directory|.artifacts/bin/%s{p}/release/%s{tfm}";
-                $"directory|.artifacts/bin/%s{p}/release";
+                $"directory|.artifacts/bin/%s{p}/release_net8.0";
                 "-a"; "true"; "--target"; p; "-f"; "github-comment"; "--output"; outputFile
             ]
         exec { run "dotnet" args }

src/Elastic.OpenTelemetry/AgentBuilder.Build.cs

@@ -67,7 +67,7 @@ internal class EmptyAgent : IAgent
 {
 	public void Dispose() { }
 
-	public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+	public ValueTask DisposeAsync() => default;
 }
 
 internal class ElasticAgent(

src/Elastic.OpenTelemetry/AgentBuilder.cs

@@ -99,8 +99,7 @@ public AgentBuilder SkipOtlpExporter()
 	/// </summary>
 	public void ConfigureOtlpExporter(Action<OtlpExporterOptions> configure, string? name = null)
 	{
-		ArgumentNullException.ThrowIfNull(configure);
-		OtlpExporterConfiguration = configure;
+		OtlpExporterConfiguration = configure ?? throw new ArgumentNullException(nameof(configure));
 		OtlpExporterName = name;
 	}
 }

src/Elastic.OpenTelemetry/Diagnostics/LoggerMessages.cs

@@ -37,7 +37,11 @@ public static void LogAgentPreamble(this ILogger logger)
 
 		logger.LogInformation("Process ID: {ProcessId}", process.Id);
 		logger.LogInformation("Process name: {ProcessName}", process.ProcessName);
+#if NET6_0_OR_GREATER
 		logger.LogInformation("Process path: {ProcessPath}", Environment.ProcessPath);
+#else
+		logger.LogInformation("Process path: {ProcessPath}", "<Unknown>");
+#endif
 
 		logger.LogInformation("Process started: {ProcessStartTime:yyyy-MM-dd HH:mm:ss.fff}", process.StartTime.ToUniversalTime());
 		logger.LogInformation("Machine name: {MachineName}", Environment.MachineName);

src/Elastic.OpenTelemetry/Diagnostics/Logging/FileLogger.cs

@@ -49,11 +49,9 @@ public FileLogger()
 		if (!Directory.Exists(path))
 			Directory.CreateDirectory(path);
 
-		_streamWriter = new StreamWriter(LogFilePath, Encoding.UTF8, new FileStreamOptions
-		{
-			Access = FileAccess.Write,
-			Mode = FileMode.OpenOrCreate,
-		});
+		//StreamWriter.Dispose disposes underlying stream too
+		var stream = new FileStream(LogFilePath, FileMode.OpenOrCreate, FileAccess.Write);
+		_streamWriter = new StreamWriter(stream, Encoding.UTF8);
 
 		WritingTask = Task.Run(async () =>
 		{
@@ -117,7 +115,13 @@ public async ValueTask DisposeAsync()
 			await WritingTask.ConfigureAwait(false);
 
 		if (_streamWriter != null)
+		{
+#if NETSTANDARD2_0 || NETFRAMEWORK
+			_streamWriter.Dispose();
+#else
 			await _streamWriter.DisposeAsync().ConfigureAwait(false);
+#endif
+		}
 	}
 
 }

src/Elastic.OpenTelemetry/Diagnostics/Logging/ScopedCompositeLogger.cs

@@ -20,7 +20,7 @@ public void Dispose()
 	}
 
 	/// <summary> TODO </summary>
-	public ValueTask DisposeAsync() => additionalLogger is IAsyncDisposable d ? d.DisposeAsync() : ValueTask.CompletedTask;
+	public ValueTask DisposeAsync() => additionalLogger is IAsyncDisposable d ? d.DisposeAsync() : default;
 
 	/// <summary> TODO </summary>
 	public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)

src/Elastic.OpenTelemetry/Diagnostics/LoggingEventListener.cs

@@ -16,8 +16,15 @@ internal sealed partial class LoggingEventListener : EventListener, IAsyncDispos
 	private readonly ILogger _logger;
 	private readonly EventLevel _eventLevel = EventLevel.Informational;
 
-	[GeneratedRegex("^\\d{2}-[a-f0-9]{32}-[a-f0-9]{16}-\\d{2}$")]
+	private const string TraceParentRegularExpressionString = "^\\d{2}-[a-f0-9]{32}-[a-f0-9]{16}-\\d{2}$";
+#if NET8_0_OR_GREATER
+	[GeneratedRegex(TraceParentRegularExpressionString)]
 	private static partial Regex TraceParentRegex();
+#else
+
+	private static Regex _traceParentRegex = new Regex(TraceParentRegularExpressionString);
+	private static Regex TraceParentRegex() => _traceParentRegex;
+#endif
 
 	public LoggingEventListener(ILogger logger)
 	{
@@ -44,7 +51,7 @@ public override void Dispose()
 	}
 
 	public ValueTask DisposeAsync() =>
-		_logger is IAsyncDisposable d ? d.DisposeAsync() : ValueTask.CompletedTask;
+		_logger is IAsyncDisposable d ? d.DisposeAsync() : default;
 
 
 	protected override void OnEventSourceCreated(EventSource eventSource)
@@ -69,20 +76,20 @@ protected override void OnEventWritten(EventWrittenEventArgs eventData)
 		// to a rented array and Span<char> if required.
 		var builder = StringBuilderCache.Acquire();
 
-		var spanId = CreateLogMessage(eventData, builder);
+#if NETSTANDARD2_0 || NETFRAMEWORK
+		var timestamp = DateTime.UtcNow; //best effort in absense of real event timestamp
+		var osThreadId = 0L;
+#else
+		var timestamp = eventData.TimeStamp;
+		var osThreadId = eventData.OSThreadId;
+#endif
 
-		try
-		{
-			// TODO - We can only get the OS thread ID from the args - Do we send that instead??
-			// As per this issue - https://github.com/dotnet/runtime/issues/13125 - OnEventWritten may be on a different thread
-			// so we can't use the Environment.CurrentManagedThreadId value here.
-			_logger.WriteLogLine(null, -1, eventData.TimeStamp, GetLogLevel(eventData), StringBuilderCache.GetStringAndRelease(builder), spanId);
-		}
-		catch (Exception)
-		{
-			// TODO - We might want to block writing further events if we reach here as it's
-			// likely a file access issue
-		}
+		var spanId = CreateLogMessage(eventData, builder, osThreadId);
+
+		// TODO - We can only get the OS thread ID from the args - Do we send that instead??
+		// As per this issue - https://github.com/dotnet/runtime/issues/13125 - OnEventWritten may be on a different thread
+		// so we can't use the Environment.CurrentManagedThreadId value here.
+		_logger.WriteLogLine(null, -1, timestamp, GetLogLevel(eventData), StringBuilderCache.GetStringAndRelease(builder), spanId);
 
 		static LogLevel GetLogLevel(EventWrittenEventArgs eventData) =>
 			eventData.Level switch
@@ -96,13 +103,13 @@ static LogLevel GetLogLevel(EventWrittenEventArgs eventData) =>
 				_ => LogLevel.None
 			};
 
-		static string? CreateLogMessage(EventWrittenEventArgs eventData, StringBuilder builder)
+		static string? CreateLogMessage(EventWrittenEventArgs eventData, StringBuilder builder, long threadId)
 		{
 			string? spanId = null;
 
 			if (eventData.EventSource.Name.StartsWith(OpenTelemetrySdkEventSourceNamePrefix) && eventData.Message is not null)
 			{
-				builder.Append($"OTEL-SDK: [{eventData.OSThreadId}] ");
+				builder.Append($"OTEL-SDK: [{threadId}] ");
 
 				if (eventData.Payload is null)
 				{

src/Elastic.OpenTelemetry/Elastic.OpenTelemetry.csproj

@@ -2,10 +2,11 @@
 
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net8.0;net6.0;net462</TargetFrameworks>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <IsPackable>True</IsPackable>
+    <PolyPublic>false</PolyPublic>
   </PropertyGroup>
 
   <ItemGroup>
@@ -18,10 +19,16 @@
     <PackageReference Include="OpenTelemetry.Instrumentation.EntityFrameworkCore" Version="1.0.0-beta.9" />
     <PackageReference Include="OpenTelemetry.Instrumentation.Runtime" Version="1.7.0" />
     <PackageReference Include="OpenTelemetry.Instrumentation.Process" Version="0.5.0-beta.4" />
+    <PackageReference Include="Polyfill" Version="3.0.0" PrivateAssets="All" 
+                      IncludeAssets="runtime; build; native; contentfiles; analyzers; buildtransitive"/>
+  </ItemGroup>
+
+  <ItemGroup Condition="$(TargetFramework.StartsWith('netstandard2')) OR $(TargetFramework.StartsWith('net4'))">
+    <PackageReference Include="System.Threading.Channels" Version="8.0.0" />
   </ItemGroup>
 
   <ItemGroup>
-    <InternalsVisibleTo Include="Elastic.OpenTelemetry.Tests" Key="$(ExposedPublicKey)" />
+    <InternalsVisibleTo Include="Elastic.OpenTelemetry.Tests" Key="$(ExposedPublicKey)"/>
   </ItemGroup>
-  
+
 </Project>

src/Elastic.OpenTelemetry/Processors/SpanCompressionProcessor.cs

@@ -13,7 +13,7 @@ namespace Elastic.OpenTelemetry.Processors;
 /// <summary> A processor that can mark spans as compressed/composite </summary>
 public class SpanCompressionProcessor : BaseProcessor<Activity>
 {
-    private readonly ConditionalWeakTable<Activity, Activity> _compressionBuffer = [];
+    private readonly ConditionalWeakTable<Activity, Activity> _compressionBuffer = new();
 
 	/// <inheritdoc cref="OnStart"/>
     public override void OnStart(Activity data)