From f652c222028ebd504203dce6a68e67b416465aab Mon Sep 17 00:00:00 2001
From: Javier Calvarro Nelson <jacalvar@microsoft.com>
Date: Sat, 15 Jun 2019 00:54:14 +0200
Subject: [PATCH] [Fixes #11183] Race condition in RouteBase.EnsureLoggers
 (#11218)

[Fixes #11183] Race condition in RouteBase.EnsureLoggers
---
 src/Http/Routing/src/RouteBase.cs | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/src/Http/Routing/src/RouteBase.cs b/src/Http/Routing/src/RouteBase.cs
index c12eaae75b..75d393a5d4 100644
--- a/src/Http/Routing/src/RouteBase.cs
+++ b/src/Http/Routing/src/RouteBase.cs
@@ -3,20 +3,19 @@
 
 using System;
 using System.Collections.Generic;
-using System.Text.Encodings.Web;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Routing.Internal;
 using Microsoft.AspNetCore.Routing.Logging;
 using Microsoft.AspNetCore.Routing.Template;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
-using Microsoft.Extensions.ObjectPool;
 
 namespace Microsoft.AspNetCore.Routing
 {
     public abstract class RouteBase : IRouter, INamedRouter
     {
+        private readonly object _loggersLock = new object();
+
         private TemplateMatcher _matcher;
         private TemplateBinder _binder;
         private ILogger _logger;
@@ -259,11 +258,25 @@ namespace Microsoft.AspNetCore.Routing
 
         private void EnsureLoggers(HttpContext context)
         {
+            // We check first using the _logger to see if the loggers have been initialized to avoid taking
+            // the lock on the most common case.
             if (_logger == null)
             {
-                var factory = context.RequestServices.GetRequiredService<ILoggerFactory>();
-                _logger = factory.CreateLogger(typeof(RouteBase).FullName);
-                _constraintLogger = factory.CreateLogger(typeof(RouteConstraintMatcher).FullName);
+                // We need to lock here to ensure that _constraintLogger and _logger get initialized atomically.
+                lock (_loggersLock)
+                {
+                    if (_logger != null)
+                    {
+                        // Multiple threads might have tried to accquire the lock at the same time. Technically
+                        // there is nothing wrong if things get reinitialized by a second thread, but its easy
+                        // to prevent by just rechecking and returning here.
+                        return;
+                    }
+
+                    var factory = context.RequestServices.GetRequiredService<ILoggerFactory>();
+                    _constraintLogger = factory.CreateLogger(typeof(RouteConstraintMatcher).FullName);
+                    _logger = factory.CreateLogger(typeof(RouteBase).FullName);
+                }
             }
         }