fix threading issue in TracingHttpModule (#655)

DataDog · Feb 21, 2020 · b43d97a · b43d97a
1 parent 12f2f6b
commit b43d97a
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Showing 2 changed files with 16 additions and 9 deletions.
diff --git a/samples-aspnet/Samples.AspNetMvc5/Web.config b/samples-aspnet/Samples.AspNetMvc5/Web.config
@@ -56,18 +56,19 @@
       <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
     </providers>
   </entityFramework>
-  
+
   <system.codedom>
     <compilers>
       <compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701" />
       <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=2.0.1.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" />
     </compilers>
   </system.codedom>
-<system.webServer>
+  <system.webServer>
     <handlers>
       <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
       <remove name="OPTIONSVerbHandler" />
       <remove name="TRACEVerbHandler" />
       <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
     </handlers>
-  </system.webServer></configuration>
+  </system.webServer>
+</configuration>
diff --git a/src/Datadog.Trace.AspNet/TracingHttpModule.cs b/src/Datadog.Trace.AspNet/TracingHttpModule.cs
@@ -1,5 +1,5 @@
 using System;
-using System.Collections.Generic;
+using System.Collections.Concurrent;
 using System.Web;
 using Datadog.Trace.ExtensionMethods;
 using Datadog.Trace.Logging;
@@ -19,7 +19,9 @@ public class TracingHttpModule : IHttpModule
 
         private static readonly Vendors.Serilog.ILogger Log = DatadogLogging.GetLogger(typeof(TracingHttpModule));
 
-        private static HashSet<HttpApplication> registeredEventHandlers = new HashSet<HttpApplication>();
+        // there is no ConcurrentHashSet, so use a ConcurrentDictionary
+        // where we only care about the key, not the value
+        private static ConcurrentDictionary<HttpApplication, byte> registeredEventHandlers = new ConcurrentDictionary<HttpApplication, byte>();
 
         private readonly string _httpContextScopeKey;
         private readonly string _requestOperationName;
@@ -56,7 +58,7 @@ public void Init(HttpApplication httpApplication)
             //         I've discovered that not letting each of these unique application objects be added, and thus
             //         the event handlers be registered within each HttpApplication object, leads to the runtime
             //         weirdness: at one point it crashed consistently for me, and later, I saw no spans at all.
-            if (registeredEventHandlers.Add(httpApplication))
+            if (registeredEventHandlers.TryAdd(httpApplication, 1))
             {
                 _httpApplication = httpApplication;
                 httpApplication.BeginRequest += OnBeginRequest;
@@ -68,9 +70,13 @@ public void Init(HttpApplication httpApplication)
         /// <inheritdoc />
         public void Dispose()
         {
-            // Remove the HttpApplication mapping so we don't keep the object alive
-            registeredEventHandlers.Remove(_httpApplication);
-            _httpApplication = null;
+            // defend against multiple calls to Dispose()
+            if (_httpApplication != null)
+            {
+                // Remove the HttpApplication mapping so we don't keep the object alive
+                registeredEventHandlers.TryRemove(_httpApplication, out var _);
+                _httpApplication = null;
+            }
         }
 
         private void OnBeginRequest(object sender, EventArgs eventArgs)