Make IHealthCheckService work in ST-sync-context

\n\nCommit migrated from 2b673c89c2

src/HealthChecks/HealthChecks/src/DefaultHealthCheckService.cs

@@ -54,7 +54,7 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
             {
                 foreach (var registration in registrations)
                 {
-                    tasks[index++] = RunCheckAsync(scope, registration, cancellationToken);
+                    tasks[index++] = Task.Run(() => RunCheckAsync(scope, registration, cancellationToken), cancellationToken);
                 }
 
                 await Task.WhenAll(tasks).ConfigureAwait(false);
@@ -75,8 +75,6 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
 
         private async Task<HealthReportEntry> RunCheckAsync(IServiceScope scope, HealthCheckRegistration registration, CancellationToken cancellationToken)
         {
-            await Task.Yield();
-
             cancellationToken.ThrowIfCancellationRequested();
 
             var healthCheck = registration.Factory(scope.ServiceProvider);
@@ -104,7 +102,7 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
                         checkCancellationToken = timeoutCancellationTokenSource.Token;
                     }
 
-                    result = await healthCheck.CheckHealthAsync(context, checkCancellationToken);
+                    result = await healthCheck.CheckHealthAsync(context, checkCancellationToken).ConfigureAwait(false);
 
                     var duration = stopwatch.GetElapsedTime();
 
@@ -118,7 +116,6 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
                     Log.HealthCheckEnd(_logger, registration, entry, duration);
                     Log.HealthCheckData(_logger, registration, entry);
                 }
-
                 catch (OperationCanceledException ex) when (!cancellationToken.IsCancellationRequested)
                 {
                     var duration = stopwatch.GetElapsedTime();

src/HealthChecks/HealthChecks/test/DefaultHealthCheckServiceTest.cs

@@ -8,6 +8,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Testing;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Internal;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Testing;
 using Microsoft.Extensions.Options;
@@ -450,6 +451,39 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
                 });
         }
 
+        [Fact]
+        public void CheckHealthAsync_WorksInSingleThreadedSyncContext()
+        {
+            // Arrange
+            var service = CreateHealthChecksService(b =>
+            {
+                b.AddAsyncCheck("test", async () =>
+                {
+                    await Task.Delay(1).ConfigureAwait(false);
+                    return HealthCheckResult.Healthy();
+                });
+            });
+
+            var hangs = true;
+
+            // Act
+            using (var cts = new CancellationTokenSource(TimeSpan.FromSeconds(3)))
+            {
+                var token = cts.Token;
+                token.Register(() => throw new OperationCanceledException(token));
+
+                SingleThreadedSynchronizationContext.Run(() =>
+                {
+                    // Act
+                    service.CheckHealthAsync(token).GetAwaiter().GetResult();
+                    hangs = false;
+                });
+            }
+
+            // Assert
+            Assert.False(hangs);
+        }
+
         private static DefaultHealthCheckService CreateHealthChecksService(Action<IHealthChecksBuilder> configure)
         {
             var services = new ServiceCollection();

src/HealthChecks/HealthChecks/test/Microsoft.Extensions.Diagnostics.HealthChecks.Tests.csproj

@@ -12,4 +12,8 @@
     <Reference Include="Microsoft.Extensions.Logging.Testing" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Compile Include="..\..\..\Shared\test\SingleThreadedSynchronizationContext.cs" Link="Shared\SingleThreadedSynchronizationContext.cs"/>
+  </ItemGroup>
+
 </Project>