Provide an (at least temporary) non-global ManagedHandler opt-in mechanism

src/CoreFx.Private.TestUtilities/ref/CoreFx.Private.TestUtilities.cs

@@ -134,6 +134,7 @@ protected RemoteExecutorTestBase() { }
         public static System.Diagnostics.RemoteExecutorTestBase.RemoteInvokeHandle RemoteInvoke(System.Func<string, string, string, string, int> method, string arg1, string arg2, string arg3, string arg4, System.Diagnostics.RemoteInvokeOptions options=null) { throw null; }
         public static System.Diagnostics.RemoteExecutorTestBase.RemoteInvokeHandle RemoteInvoke(System.Func<string, string, string, string, string, int> method, string arg1, string arg2, string arg3, string arg4, string arg5, System.Diagnostics.RemoteInvokeOptions options=null) { throw null; }
         public static System.Diagnostics.RemoteExecutorTestBase.RemoteInvokeHandle RemoteInvoke(System.Func<System.Threading.Tasks.Task<int>> method, System.Diagnostics.RemoteInvokeOptions options=null) { throw null; }
+        public static System.Diagnostics.RemoteExecutorTestBase.RemoteInvokeHandle RemoteInvoke(System.Func<string, System.Threading.Tasks.Task<int>> method, string arg, System.Diagnostics.RemoteInvokeOptions options=null) { throw null; }
         public static System.Diagnostics.RemoteExecutorTestBase.RemoteInvokeHandle RemoteInvokeRaw(System.Delegate method, string unparsedArg, System.Diagnostics.RemoteInvokeOptions options=null) { throw null; }
         public sealed partial class RemoteInvokeHandle : System.IDisposable
         {

src/CoreFx.Private.TestUtilities/src/System/Diagnostics/RemoteExecutorTestBase.cs

@@ -42,6 +42,17 @@ public static RemoteInvokeHandle RemoteInvoke(
             return RemoteInvoke(GetMethodInfo(method), Array.Empty<string>(), options);
         }
 
+        /// <summary>Invokes the method from this assembly in another process using the specified arguments.</summary>
+        /// <param name="method">The method to invoke.</param>
+        /// <param name="options">Options to use for the invocation.</param>
+        public static RemoteInvokeHandle RemoteInvoke(
+            Func<string, Task<int>> method,
+            string arg,
+            RemoteInvokeOptions options = null)
+        {
+            return RemoteInvoke(GetMethodInfo(method), new[] { arg }, options);
+        }
+
         /// <summary>Invokes the method from this assembly in another process using the specified arguments.</summary>
         /// <param name="method">The method to invoke.</param>
         /// <param name="arg1">The first argument to pass to the method.</param>

src/System.IO.MemoryMappedFiles/tests/MemoryMappedFile.CrossProcess.cs

@@ -27,7 +27,7 @@ public void DataShared()
                 acc.Flush();
 
                 // Spawn and then wait for the other process, which will verify the data and write its own known pattern
-                RemoteInvoke(DataShared_OtherProcess, file.Path).Dispose();
+                RemoteInvoke(new Func<string, int>(DataShared_OtherProcess), file.Path).Dispose();
 
                 // Now verify we're seeing the data from the other process
                 for (int i = 0; i < capacity; i++)

src/System.Net.Http/src/System.Net.Http.csproj

@@ -450,6 +450,7 @@
     <Reference Include="System.Text.Encoding" />
     <Reference Include="System.Text.Encoding.Extensions" />
     <Reference Include="System.Threading" />
+    <Reference Include="System.Threading.Thread" />
     <Reference Include="System.Threading.Tasks" />
     <Reference Include="System.Threading.Tasks.Extensions" />
     <Reference Include="System.Threading.Timer" />

src/System.Net.Http/src/System/Net/Http/HttpClientHandler.cs

@@ -2,16 +2,52 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics;
 using System.Net.Security;
 using System.Security.Cryptography.X509Certificates;
+using System.Threading;
 
 namespace System.Net.Http
 {
     public partial class HttpClientHandler : HttpMessageHandler
     {
         // This partial implementation contains members common to all HttpClientHandler implementations.
-
-        private static bool UseManagedHandler => Environment.GetEnvironmentVariable("COMPlus_UseManagedHttpClientHandler") == "true";
+        private const string ManagedHandlerSettingName = "COMPlus_UseManagedHttpClientHandler";
+
+        private static LocalDataStoreSlot s_useManagedHandlerSlot;
+
+        private static bool UseManagedHandler
+        {
+            get
+            {
+                // Check the environment variable to see if it's been set to true.  If it has, use the managed handler.
+                if (Environment.GetEnvironmentVariable(ManagedHandlerSettingName) == "true")
+                {
+                    return true;
+                }
+
+                // Then check whether a thread local has been set with the same name.
+                // If it's been set to a Boolean true, also use the managed handler.
+                LocalDataStoreSlot slot = LazyInitializer.EnsureInitialized(ref s_useManagedHandlerSlot, () =>
+                {
+                    LocalDataStoreSlot local = Thread.GetNamedDataSlot(ManagedHandlerSettingName);
+                    if (local == null)
+                    {
+                        try
+                        {
+                            local = Thread.AllocateNamedDataSlot(ManagedHandlerSettingName);
+                        }
+                        catch (ArgumentException)
+                        {
+                            local = Thread.GetNamedDataSlot(ManagedHandlerSettingName);
+                        }
+                    }
+                    return local;
+                });
+                Debug.Assert(slot != null);
+                return Thread.GetData(slot) is bool result && result;
+            }
+        }
 
         public static Func<HttpRequestMessage, X509Certificate2, X509Chain, SslPolicyErrors, bool> DangerousAcceptAnyServerCertificateValidator { get; } = delegate { return true; };
     }

src/System.Net.Http/tests/FunctionalTests/CancellationTest.cs

@@ -13,7 +13,7 @@
 
 namespace System.Net.Http.Functional.Tests
 {
-    public class CancellationTest
+    public class CancellationTest : HttpClientTestBase
     {
         private readonly ITestOutputHelper _output;
 
@@ -37,8 +37,10 @@ public async Task GetAsync_ResponseContentRead_CancelUsingTimeoutOrToken_TaskCan
             TimeSpan timeout = useTimeout ? new TimeSpan(0, 0, 1) : Timeout.InfiniteTimeSpan;
             CancellationToken cancellationToken = useTimeout ? CancellationToken.None : cts.Token;
 
-            using (var client = new HttpClient() { Timeout = timeout })
+            using (HttpClient client = CreateHttpClient())
             {
+                client.Timeout = timeout;
+
                 var triggerResponseWrite = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
                 var triggerRequestCancel = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
 
@@ -107,7 +109,7 @@ public Task ReadAsStreamAsync_ReadAsync_Cancel_BodyNeverStarted_TaskCanceledQuic
         [InlineData(true)]
         public async Task ReadAsStreamAsync_ReadAsync_Cancel_TaskCanceledQuickly(bool startResponseBody)
         {
-            using (var client = new HttpClient())
+            using (HttpClient client = CreateHttpClient())
             {
                 await LoopbackServer.CreateServerAsync(async (server, url) =>
                 {

src/System.Net.Http/tests/FunctionalTests/DefaultCredentialsTest.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Net.Test.Common;
 using System.Security.Principal;
 using System.Threading.Tasks;
 
@@ -16,7 +15,7 @@ namespace System.Net.Http.Functional.Tests
     // TODO: #2383 - Consolidate the use of the environment variable settings to Common/tests.
     [SkipOnTargetFramework(TargetFrameworkMonikers.Uap, "dotnet/corefx #20010")]
     [PlatformSpecific(TestPlatforms.Windows)]
-    public class DefaultCredentialsTest
+    public class DefaultCredentialsTest : HttpClientTestBase
     {
         private static string DomainJoinedTestServer => Configuration.Http.DomainJoinedHttpHost;
         private static bool DomainJoinedTestsEnabled => !string.IsNullOrEmpty(DomainJoinedTestServer);
@@ -51,7 +50,7 @@ public DefaultCredentialsTest(ITestOutputHelper output)
         [InlineData(true)]
         public async Task UseDefaultCredentials_DefaultValue_Unauthorized(bool useProxy)
         {
-            var handler = new HttpClientHandler();
+            HttpClientHandler handler = CreateHttpClientHandler();
             handler.UseProxy = useProxy;
 
             using (var client = new HttpClient(handler))
@@ -68,7 +67,9 @@ public async Task UseDefaultCredentials_DefaultValue_Unauthorized(bool useProxy)
         [InlineData(true)]
         public async Task UseDefaultCredentials_SetFalse_Unauthorized(bool useProxy)
         {
-            var handler = new HttpClientHandler { UseProxy = useProxy, UseDefaultCredentials = false };
+            HttpClientHandler handler = CreateHttpClientHandler();
+            handler.UseProxy = useProxy;
+            handler.UseDefaultCredentials = false;
 
             using (var client = new HttpClient(handler))
             using (HttpResponseMessage response = await client.GetAsync(s_authenticatedServer))
@@ -84,7 +85,9 @@ public async Task UseDefaultCredentials_SetFalse_Unauthorized(bool useProxy)
         [InlineData(true)]
         public async Task UseDefaultCredentials_SetTrue_ConnectAsCurrentIdentity(bool useProxy)
         {
-            var handler = new HttpClientHandler { UseProxy = useProxy, UseDefaultCredentials = true };
+            HttpClientHandler handler = CreateHttpClientHandler();
+            handler.UseProxy = useProxy;
+            handler.UseDefaultCredentials = true;
 
             using (var client = new HttpClient(handler))
             using (HttpResponseMessage response = await client.GetAsync(s_authenticatedServer))
@@ -105,7 +108,9 @@ public async Task UseDefaultCredentials_SetTrue_ConnectAsCurrentIdentity(bool us
         [InlineData(true)]
         public async Task UseDefaultCredentials_SetTrueAndServerOffersMultipleSchemes_Ok(bool useProxy)
         {
-            var handler = new HttpClientHandler { UseProxy = useProxy, UseDefaultCredentials = true };
+            HttpClientHandler handler = CreateHttpClientHandler();
+            handler.UseProxy = useProxy;
+            handler.UseDefaultCredentials = true;
 
             using (var client = new HttpClient(handler))
             using (HttpResponseMessage response = await client.GetAsync(s_multipleSchemesAuthenticatedServer))
@@ -126,10 +131,10 @@ public async Task UseDefaultCredentials_SetTrueAndServerOffersMultipleSchemes_Ok
         [InlineData(true)]
         public async Task Credentials_SetToSpecificCredential_ConnectAsSpecificIdentity(bool useProxy)
         {
-            var handler = new HttpClientHandler {
-                UseProxy = useProxy,
-                UseDefaultCredentials = false,
-                Credentials = _specificCredential };
+            HttpClientHandler handler = CreateHttpClientHandler();
+            handler.UseProxy = useProxy;
+            handler.UseDefaultCredentials = false;
+            handler.Credentials = _specificCredential;
 
             using (var client = new HttpClient(handler))
             using (HttpResponseMessage response = await client.GetAsync(s_authenticatedServer))
@@ -148,7 +153,7 @@ public async Task Credentials_SetToSpecificCredential_ConnectAsSpecificIdentity(
         [InlineData(true)]
         public async Task Credentials_SetToWrappedDefaultCredential_ConnectAsCurrentIdentity(bool useProxy)
         {
-            var handler = new HttpClientHandler();
+            HttpClientHandler handler = CreateHttpClientHandler();
             handler.UseProxy = useProxy;
             handler.Credentials = new CredentialWrapper
             {
@@ -172,7 +177,7 @@ public async Task Credentials_SetToWrappedDefaultCredential_ConnectAsCurrentIden
         [ConditionalFact(nameof(DomainProxyTestsEnabled))]
         public async Task Proxy_UseAuthenticatedProxyWithNoCredentials_ProxyAuthenticationRequired()
         {
-            var handler = new HttpClientHandler();
+            HttpClientHandler handler = CreateHttpClientHandler();
             handler.Proxy = new AuthenticatedProxy(null);
 
             using (var client = new HttpClient(handler))
@@ -187,7 +192,7 @@ public async Task Proxy_UseAuthenticatedProxyWithNoCredentials_ProxyAuthenticati
         [ConditionalFact(nameof(DomainProxyTestsEnabled))]
         public async Task Proxy_UseAuthenticatedProxyWithDefaultCredentials_OK()
         {
-            var handler = new HttpClientHandler();
+            HttpClientHandler handler = CreateHttpClientHandler();
             handler.Proxy = new AuthenticatedProxy(CredentialCache.DefaultCredentials);
 
             using (var client = new HttpClient(handler))
@@ -206,7 +211,7 @@ public async Task Proxy_UseAuthenticatedProxyWithWrappedDefaultCredentials_OK()
                 InnerCredentials = CredentialCache.DefaultCredentials
             };
 
-            var handler = new HttpClientHandler();
+            HttpClientHandler handler = CreateHttpClientHandler();
             handler.Proxy = new AuthenticatedProxy(wrappedCreds);
 
             using (var client = new HttpClient(handler))