[release/9.4] Force async execution of resource startup (#10360)

* Force async execution of resource startup - Previously we didn't preemptively dispatch to the threadpool per resource on startup. That causes issues blocking other resource's startup because of a single blocking call. This change dispatching preemptively before creating the dcp resource.

* Refactor ParameterResource to use Lazy initialization for value retrieval (#10361)

---------

Co-authored-by: David Fowler <davidfowl@gmail.com>

Author: github-actions[bot]

src/Aspire.Hosting/ApplicationModel/ParameterResource.cs

@@ -8,8 +8,7 @@ namespace Aspire.Hosting.ApplicationModel;
 /// </summary>
 public class ParameterResource : Resource, IResourceWithoutLifetime, IManifestExpressionProvider, IValueProvider
 {
-    private string? _value;
-    private bool _hasValue;
+    private readonly Lazy<string> _lazyValue;
     private readonly Func<ParameterDefault?, string> _valueGetter;
     private string? _configurationKey;
 
@@ -25,6 +24,7 @@ public ParameterResource(string name, Func<ParameterDefault?, string> callback,
         ArgumentNullException.ThrowIfNull(callback);
 
         _valueGetter = callback;
+        _lazyValue = new Lazy<string>(() => _valueGetter(Default));
         Secret = secret;
     }
 
@@ -33,18 +33,7 @@ public ParameterResource(string name, Func<ParameterDefault?, string> callback,
     /// </summary>
     public string Value => GetValueAsync(default).AsTask().GetAwaiter().GetResult()!;
 
-    internal string ValueInternal
-    {
-        get
-        {
-            if (!_hasValue)
-            {
-                _value = _valueGetter(Default);
-                _hasValue = true;
-            }
-            return _value!;
-        }
-    }
+    internal string ValueInternal => _lazyValue.Value;
 
     /// <summary>
     /// Represents how the default value of the parameter should be retrieved.

src/Aspire.Hosting/Dcp/DcpExecutor.cs

@@ -1097,6 +1097,9 @@ async Task CreateResourceExecutablesAsyncCore(IResource resource, IEnumerable<Ap
 
     private async Task CreateExecutableAsync(AppResource er, ILogger resourceLogger, CancellationToken cancellationToken)
     {
+        // Force async execution
+        await Task.Yield();
+
         if (er.DcpResource is not Executable exe)
         {
             throw new InvalidOperationException($"Expected an Executable resource, but got {er.DcpResource.Kind} instead");
@@ -1348,6 +1351,9 @@ async Task CreateContainerAsyncCore(AppResource cr, CancellationToken cancellati
 
     private async Task CreateContainerAsync(AppResource cr, ILogger resourceLogger, CancellationToken cancellationToken)
     {
+        // Force async execution
+        await Task.Yield();
+
         await _executorEvents.PublishAsync(new OnResourceStartingContext(cancellationToken, KnownResourceTypes.Container, cr.ModelResource, cr.DcpResource.Metadata.Name)).ConfigureAwait(false);
 
         var dcpContainerResource = (Container)cr.DcpResource;