Increase HttpClientHandler.MaxConnectionsPerServer to 64 to improve PM UI performance in Visual Studio

src/NuGet.Core/NuGet.Protocol/HttpSource/HttpHandlerResourceV3Provider.cs

@@ -48,6 +48,13 @@ private static HttpHandlerResourceV3 CreateResource(PackageSource packageSource)
                 AutomaticDecompression = (DecompressionMethods.GZip | DecompressionMethods.Deflate)
             };
 
+#if IS_DESKTOP
+            if (packageSource.MaxHttpRequestsPerSource > 0)
+            {
+                clientHandler.MaxConnectionsPerServer = packageSource.MaxHttpRequestsPerSource;
+            }
+#endif
+
             // Setup http client handler client certificates
             if (packageSource.ClientCertificates != null)
             {

src/NuGet.Core/NuGet.Protocol/HttpSource/HttpSourceResourceProvider.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Concurrent;
 using System.Diagnostics;
+using System.Net;
 using System.Threading;
 using System.Threading.Tasks;
 using NuGet.Configuration;
@@ -13,6 +14,9 @@ namespace NuGet.Protocol
 {
     public class HttpSourceResourceProvider : ResourceProvider
     {
+#if IS_DESKTOP
+        private const int DefaultMaxHttpRequestsPerSource = 64;
+#endif
         // Only one HttpSource per source should exist. This is to reduce the number of TCP connections.
         private readonly ConcurrentDictionary<PackageSource, HttpSourceResource> _cache
             = new ConcurrentDictionary<PackageSource, HttpSourceResource>();
@@ -47,6 +51,12 @@ public override Task<Tuple<bool, INuGetResource>> TryCreate(SourceRepository sou
                 {
                     throttle = SemaphoreSlimThrottle.CreateSemaphoreThrottle(source.PackageSource.MaxHttpRequestsPerSource);
                 }
+#if IS_DESKTOP
+                else if (ServicePointManager.DefaultConnectionLimit == ServicePointManager.DefaultPersistentConnectionLimit)
+                {
+                    source.PackageSource.MaxHttpRequestsPerSource = DefaultMaxHttpRequestsPerSource;
+                }
+#endif
 
                 curResource = _cache.GetOrAdd(
                     source.PackageSource,

test/NuGet.Core.Tests/NuGet.Protocol.Tests/HttpHandlerResourceV3ProviderTests.cs

@@ -0,0 +1,85 @@
+// 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.Collections.Generic;
+using System.Threading.Tasks;
+using NuGet.Configuration;
+using NuGet.Protocol.Core.Types;
+using NuGet.Test.Utility;
+using Xunit;
+
+namespace NuGet.Protocol.Tests
+{
+    public class HttpHandlerResourceV3ProviderTests
+    {
+        private readonly string _testPackageSourceURL = "https://contoso.test/v3/index.json";
+
+#if IS_DESKTOP
+        [PlatformFact(Platform.Windows)]
+        public async Task DefaultMaxHttpRequestsPerSourceIsForwardedToV3HttpClientHandler_SuccessAsync()
+        {
+            // Arrange
+            var packageSource = new PackageSource(_testPackageSourceURL);
+            var sourceRepository = new SourceRepository(packageSource, new List<INuGetResourceProvider>() { new HttpSourceResourceProvider(), new HttpHandlerResourceV3Provider() });
+
+            // HttpSourceResourceProvider updates PackageSource.MaxHttpRequestsPerSource value for .NET Framework code paths
+            // HttpSource constructor accepts a delegate that creates HttpHandlerResource and it stores the delegate in a private variable.
+            // Hence used discard to ignore the return value and fetched HttpHandlerResource from the source repository to verify behavior. 
+            _ = await sourceRepository.GetResourceAsync<HttpSourceResource>();
+
+            // Act
+            HttpHandlerResource httpHandlerResource = await sourceRepository.GetResourceAsync<HttpHandlerResource>();
+
+            // Assert
+            Assert.NotNull(httpHandlerResource);
+            Assert.Equal(64, httpHandlerResource.ClientHandler.MaxConnectionsPerServer);
+        }
+
+        [PlatformTheory(Platform.Windows)]
+        [InlineData(128)]
+        [InlineData(256)]
+        public async Task PackageSourceMaxHttpRequestsPerSourceIsForwardedToV3HttpClientHandler_SuccessAsync(int maxHttpRequestsPerSource)
+        {
+            // Arrange
+            var packageSource = new PackageSource(_testPackageSourceURL) { MaxHttpRequestsPerSource = maxHttpRequestsPerSource };
+            var sourceRepository = new SourceRepository(packageSource, new List<INuGetResourceProvider>() { new HttpSourceResourceProvider(), new HttpHandlerResourceV3Provider() });
+
+            // HttpSourceResourceProvider updates PackageSource.MaxHttpRequestsPerSource value for .NET Framework code paths
+            // HttpSource constructor accepts a delegate that creates HttpHandlerResource and it stores the delegate in a private variable.
+            // Hence used discard to ignore the return value and fetched HttpHandlerResource from the source repository to verify behavior.
+            _ = await sourceRepository.GetResourceAsync<HttpSourceResource>();
+
+            // Act            
+            HttpHandlerResource httpHandlerResource = await sourceRepository.GetResourceAsync<HttpHandlerResource>();
+
+            // Assert
+            Assert.NotNull(httpHandlerResource);
+            Assert.Equal(maxHttpRequestsPerSource, httpHandlerResource.ClientHandler.MaxConnectionsPerServer);
+        }
+#elif IS_CORECLR
+
+        [Theory]
+        [InlineData(64)]
+        [InlineData(128)]
+        [InlineData(2)]
+        public async Task PackageSourceMaxHttpRequestsPerSourceIsNotForwardedToV3HttpClientHandler_SuccessAsync(int maxHttpRequestsPerSource)
+        {
+            // Arrange
+            var packageSource = new PackageSource(_testPackageSourceURL) { MaxHttpRequestsPerSource = maxHttpRequestsPerSource };
+            var sourceRepository = new SourceRepository(packageSource, new[] { new HttpHandlerResourceV3Provider() });
+
+            // HttpSourceResourceProvider updates PackageSource.MaxHttpRequestsPerSource value for .NET Framework code paths
+            // HttpSource constructor accepts a delegate that creates HttpHandlerResource and it stores the delegate in a private variable.
+            // Hence used discard to ignore the return value and fetched HttpHandlerResource from the source repository to verify behavior.
+            _ = await sourceRepository.GetResourceAsync<HttpSourceResource>();
+
+            // Act            
+            HttpHandlerResource httpHandlerResource = await sourceRepository.GetResourceAsync<HttpHandlerResource>();
+
+            // Assert
+            Assert.NotNull(httpHandlerResource);
+            Assert.NotEqual(maxHttpRequestsPerSource, httpHandlerResource.ClientHandler.MaxConnectionsPerServer);
+        }
+#endif
+    }
+}

test/NuGet.Core.Tests/NuGet.Protocol.Tests/HttpSourceResourceProviderTests.cs

@@ -0,0 +1,65 @@
+// 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.Threading.Tasks;
+using NuGet.Configuration;
+using NuGet.Protocol.Core.Types;
+using NuGet.Test.Utility;
+using Xunit;
+
+namespace NuGet.Protocol.Tests
+{
+    public class HttpSourceResourceProviderTests
+    {
+        private readonly string _testPackageSourceURL = "https://contoso.test/v3/index.json";
+
+#if IS_DESKTOP
+        [PlatformFact(Platform.Windows)]
+        public async Task WhenMaxHttpRequestsPerSourceIsNotConfiguredThenItsValueIsSetToDefault_SuccessAsync()
+        {
+            // Arrange
+            var packageSource = new PackageSource(_testPackageSourceURL);
+            var sourceRepository = new SourceRepository(packageSource, new[] { new HttpSourceResourceProvider() });
+
+            // Act
+            HttpSourceResource httpSourceResource = await sourceRepository.GetResourceAsync<HttpSourceResource>();
+
+            // Assert
+            Assert.NotNull(httpSourceResource);
+            Assert.Equal(64, sourceRepository.PackageSource.MaxHttpRequestsPerSource);
+        }
+#elif IS_CORECLR
+        [Fact]
+        public async Task WhenMaxHttpRequestsPerSourceIsNotConfiguredThenItsValueWillNotBeUpdated_SuccessAsync()
+        {
+            // Arrange
+            var packageSource = new PackageSource(_testPackageSourceURL);
+            var sourceRepository = new SourceRepository(packageSource, new[] { new HttpSourceResourceProvider() });
+
+            // Act
+            HttpSourceResource httpSourceResource = await sourceRepository.GetResourceAsync<HttpSourceResource>();
+
+            // Assert
+            Assert.NotNull(httpSourceResource);
+            Assert.Equal(0, sourceRepository.PackageSource.MaxHttpRequestsPerSource);
+        }
+#endif
+
+        [PlatformTheory]
+        [InlineData(128)]
+        [InlineData(256)]
+        public async Task WhenMaxHttpRequestsPerSourceIsConfiguredThenItsValueWillNotBeUpdated_SuccessAsync(int maxHttpRequestsPerSource)
+        {
+            // Arrange
+            var packageSource = new PackageSource(_testPackageSourceURL) { MaxHttpRequestsPerSource = maxHttpRequestsPerSource };
+            var sourceRepository = new SourceRepository(packageSource, new[] { new HttpSourceResourceProvider() });
+
+            // Act
+            HttpSourceResource httpSourceResource = await sourceRepository.GetResourceAsync<HttpSourceResource>();
+
+            // Assert
+            Assert.NotNull(httpSourceResource);
+            Assert.Equal(maxHttpRequestsPerSource, sourceRepository.PackageSource.MaxHttpRequestsPerSource);
+        }
+    }
+}