Feature (#189)

* Add xml comment

* fix: LocalSegment relationship error when use Task.WhenAll

build/common.props

-<Project>
+<Project>
   <Import Project="sign.props" />
   <Import Project="version.props" />
   <PropertyGroup>
@@ -15,6 +15,8 @@
     <GenerateAssemblyCompanyAttribute>True</GenerateAssemblyCompanyAttribute>
     <GenerateAssemblyProductAttribute>True</GenerateAssemblyProductAttribute>
     <GeneratePackageOnBuild>False</GeneratePackageOnBuild>
-    <PackageRequireLicenseAcceptance>True</PackageRequireLicenseAcceptance>  
+    <PackageRequireLicenseAcceptance>True</PackageRequireLicenseAcceptance>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <NoWarn>1591</NoWarn>
   </PropertyGroup>
-</Project>
+</Project>
\ No newline at end of file

src/SkyApm.Abstractions/Tracing/Segments/SegmentSpan.cs

-/*
+/*
  * Licensed to the SkyAPM under one or more
  * contributor license agreements.  See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
@@ -42,8 +42,8 @@ namespace SkyApm.Tracing.Segments
 
         public SpanLayer SpanLayer { get; set; }
 
+        /// <summary>Limiting values. Please see <see cref="Components" /> or see <seealso href="https://github.com/apache/incubator-skywalking/blob/master/oap-server/server-starter/src/main/resources/component-libraries.yml"/></summary>
         public StringOrIntValue Component { get; set; }
-
         public bool IsError { get; set; }
         public TagCollection Tags { get; } = new TagCollection();
 
@@ -187,4 +187,4 @@ namespace SkyApm.Tracing.Segments
             return new LogEvent("stack", value);
         }
     }
-}
+}
\ No newline at end of file

src/SkyApm.Core/Tracing/LocalSegmentContextAccessor.cs

-/*
+/*
  * Licensed to the SkyAPM under one or more
  * contributor license agreements.  See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
@@ -16,55 +16,34 @@
  *
  */
 
-using System.Collections.Concurrent;
-using System.Threading;
 using SkyApm.Tracing.Segments;
+using System.Runtime.CompilerServices;
+using System.Threading;
 
 namespace SkyApm.Tracing
 {
     public class LocalSegmentContextAccessor : ILocalSegmentContextAccessor
     {
-        private readonly AsyncLocal<ConcurrentStack<SegmentContext>> _segmentContextStack =
-            new AsyncLocal<ConcurrentStack<SegmentContext>>();
+        private readonly ConditionalWeakTable<SegmentContext, SegmentContext> _parent = new ConditionalWeakTable<SegmentContext, SegmentContext>();
+        private readonly AsyncLocal<SegmentContext> _segmentContext = new AsyncLocal<SegmentContext>();
 
         public SegmentContext Context
         {
-            get
-            {
-                var stack = _segmentContextStack.Value;
-                if (stack == null)
-                {
-                    return null;
-                }
-                stack.TryPeek(out var context);
-                return context;
-            }
+            get => _segmentContext.Value;
             set
             {
-                var stack = _segmentContextStack.Value;
-                if (stack == null)
+                var current = _segmentContext.Value;
+                if (value == null)
                 {
-                    if (value == null) return;
-                    stack = new ConcurrentStack<SegmentContext>();
-                    stack.Push(value);
-                    _segmentContextStack.Value = stack;
+                    if (_parent.TryGetValue(current, out var parent))
+                        _segmentContext.Value = parent;
                 }
                 else
                 {
-                    if (value == null)
-                    {
-                        stack.TryPop(out _);
-                        if (stack.IsEmpty)
-                        {
-                            _segmentContextStack.Value = null;
-                        }
-                    }
-                    else
-                    {
-                        stack.Push(value);
-                    }
+                    _parent.Add(value, current);
+                    _segmentContext.Value = value;
                 }
             }
         }
     }
-}
+}
\ No newline at end of file