Don't use a GUID for request ID because it's slow:

- FastHttpRequestIdentifierFeature uses an incrementing long with an int seed
- Everything is lazy so no computer incurred if ID is not asked for
- Optimized routine to stringify the ID
- #306

src/Microsoft.AspNet.Hosting/Internal/FastHttpRequestIdentifierFeature.cs

@@ -0,0 +1,60 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Threading;
+using Microsoft.AspNet.Http.Features;
+
+namespace Microsoft.AspNet.Hosting.Internal
+{
+    public class FastHttpRequestIdentifierFeature : IHttpRequestIdentifierFeature
+    {
+        private static readonly string _hexChars = "0123456789ABCDEF";
+        // Seed the _requestId for this application instance with a random int
+        private static long _requestId = new Random().Next();
+        
+        private string _id = null;
+        
+        public string TraceIdentifier
+        {
+            get
+            {
+                // Don't incur the cost of generating the request ID until it's asked for
+                if (_id == null)
+                {
+                    _id = GenerateRequestId(Interlocked.Increment(ref _requestId));
+                }
+                return _id;
+            }
+            set
+            {
+                _id = value;
+            }
+        }
+
+        private static string GenerateRequestId(long id)
+        {
+            // The following routine is ~33% faster than calling long.ToString() when testing in tight loops of
+            // 1 million iterations.
+            var charBuffer = new char[sizeof(long) * 2];
+            charBuffer[0] = _hexChars[(int)(id >> 60) & 0x0f];
+            charBuffer[1] = _hexChars[(int)(id >> 56) & 0x0f];
+            charBuffer[2] = _hexChars[(int)(id >> 52) & 0x0f];
+            charBuffer[3] = _hexChars[(int)(id >> 48) & 0x0f];
+            charBuffer[4] = _hexChars[(int)(id >> 44) & 0x0f];
+            charBuffer[5] = _hexChars[(int)(id >> 40) & 0x0f];
+            charBuffer[6] = _hexChars[(int)(id >> 36) & 0x0f];
+            charBuffer[7] = _hexChars[(int)(id >> 32) & 0x0f];
+            charBuffer[8] = _hexChars[(int)(id >> 28) & 0x0f];
+            charBuffer[9] = _hexChars[(int)(id >> 24) & 0x0f];
+            charBuffer[10] = _hexChars[(int)(id >> 20) & 0x0f];
+            charBuffer[11] = _hexChars[(int)(id >> 16) & 0x0f];
+            charBuffer[12] = _hexChars[(int)(id >> 12) & 0x0f];
+            charBuffer[13] = _hexChars[(int)(id >> 8) & 0x0f];
+            charBuffer[14] = _hexChars[(int)(id >> 4) & 0x0f];
+            charBuffer[15] = _hexChars[(int)(id >> 0) & 0x0f];
+
+            return new string(charBuffer);
+        }
+    }
+}

src/Microsoft.AspNet.Hosting/Internal/HostingEngine.cs

@@ -12,7 +12,6 @@ using Microsoft.AspNet.Hosting.Server;
 using Microsoft.AspNet.Hosting.Startup;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Http.Features;
-using Microsoft.AspNet.Http.Features.Internal;
 using Microsoft.AspNet.Server.Features;
 using Microsoft.Dnx.Runtime;
 using Microsoft.Extensions.Configuration;
@@ -278,10 +277,7 @@ namespace Microsoft.AspNet.Hosting.Internal
             var requestIdentifierFeature = httpContext.Features.Get<IHttpRequestIdentifierFeature>();
             if (requestIdentifierFeature == null)
             {
-                requestIdentifierFeature = new HttpRequestIdentifierFeature()
-                {
-                    TraceIdentifier = Guid.NewGuid().ToString()
-                };
+                requestIdentifierFeature = new FastHttpRequestIdentifierFeature();
                 httpContext.Features.Set(requestIdentifierFeature);
             }
 

test/Microsoft.AspNet.Hosting.Tests/HostingEngineTests.cs

@@ -305,7 +305,7 @@ namespace Microsoft.AspNet.Hosting
 
             // Assert
             Assert.NotNull(httpContext);
-            Assert.IsType<HttpRequestIdentifierFeature>(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
+            Assert.IsType<FastHttpRequestIdentifierFeature>(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
         }
 
         [Fact]
@@ -328,7 +328,7 @@ namespace Microsoft.AspNet.Hosting
 
             // Assert
             Assert.NotNull(httpContext);
-            Assert.IsType<HttpRequestIdentifierFeature>(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
+            Assert.IsType<FastHttpRequestIdentifierFeature>(httpContext.Features.Get<IHttpRequestIdentifierFeature>());
         }
 
         [Fact]

test/Microsoft.AspNet.Hosting.Tests/Internal/FastHttpRequestIdentifierFeatureTests.cs

@@ -0,0 +1,44 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNet.Hosting.Internal;
+using Xunit;
+
+namespace Microsoft.AspNet.Hosting.Tests.Internal
+{
+    public class FastHttpRequestIdentifierFeatureTests
+    {
+        [Fact]
+        public void TraceIdentifier_ReturnsId()
+        {
+            var feature = new FastHttpRequestIdentifierFeature();
+
+            var id = feature.TraceIdentifier;
+
+            Assert.NotNull(id);
+        }
+
+        [Fact]
+        public void TraceIdentifier_ReturnsStableId()
+        {
+            var feature = new FastHttpRequestIdentifierFeature();
+
+            var id1 = feature.TraceIdentifier;
+            var id2 = feature.TraceIdentifier;
+
+            Assert.Equal(id1, id2);
+        }
+
+        [Fact]
+        public void TraceIdentifier_ReturnsUniqueIdForDifferentInstances()
+        {
+            var feature1 = new FastHttpRequestIdentifierFeature();
+            var feature2 = new FastHttpRequestIdentifierFeature();
+
+            var id1 = feature1.TraceIdentifier;
+            var id2 = feature2.TraceIdentifier;
+
+            Assert.NotEqual(id1, id2);
+        }
+    }
+}