From e73d0fb5754319bf3fc25aa961ebc34435bdd0a8 Mon Sep 17 00:00:00 2001
From: Pranav K <prkrishn@hotmail.com>
Date: Tue, 28 Apr 2020 12:28:55 -0700
Subject: [PATCH] Fixup ProcessAsync_AwaitersUseTheResultOfExecutor (#21274)

This test simulates concurrent calls on a CacheTagHelper to ensure only one enters a critical section.
However it re-uses a TagHelperOutput instance that's modified concurrently which isn't valid or what happens at runtime.

Fixes https://github.com/dotnet/aspnetcore/issues/20825
---
 .../Mvc.TagHelpers/test/CacheTagHelperTest.cs | 30 ++++++++++---------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/src/Mvc/Mvc.TagHelpers/test/CacheTagHelperTest.cs b/src/Mvc/Mvc.TagHelpers/test/CacheTagHelperTest.cs
index 3ddffe5bd3..90313c0efa 100644
--- a/src/Mvc/Mvc.TagHelpers/test/CacheTagHelperTest.cs
+++ b/src/Mvc/Mvc.TagHelpers/test/CacheTagHelperTest.cs
@@ -908,26 +908,28 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             };
 
             var invokeCount = 0;
-            var tagHelperOutput = new TagHelperOutput(
-                "cache",
-                new TagHelperAttributeList(),
-                getChildContentAsync: (useCachedResult, _) =>
-                {
-                    invokeCount++;
 
-                    var content = new DefaultTagHelperContent();
-                    content.SetContent(expected);
-                    return Task.FromResult<TagHelperContent>(content);
-                });
+            Func<bool, HtmlEncoder, Task<TagHelperContent>> getChildContentAsync = (useCachedResult, _) =>
+            {
+                invokeCount++;
+
+                var content = new DefaultTagHelperContent();
+                content.SetContent(expected);
+                return Task.FromResult<TagHelperContent>(content);
+            };
+
+            var tagHelperOutput1 = new TagHelperOutput("cache", new TagHelperAttributeList(), getChildContentAsync);
+            var tagHelperOutput2 = new TagHelperOutput("cache", new TagHelperAttributeList(), getChildContentAsync);
 
             // Act
-            var task1 = Task.Run(() => cacheTagHelper1.ProcessAsync(GetTagHelperContext(cache.Key1), tagHelperOutput));
-            var task2 = Task.Run(() => cacheTagHelper2.ProcessAsync(GetTagHelperContext(cache.Key2), tagHelperOutput));
+            var task1 = Task.Run(() => cacheTagHelper1.ProcessAsync(GetTagHelperContext(cache.Key1), tagHelperOutput1));
+            var task2 = Task.Run(() => cacheTagHelper2.ProcessAsync(GetTagHelperContext(cache.Key2), tagHelperOutput2));
 
             // Assert
             await Task.WhenAll(task1, task2);
-            Assert.Equal(encoder.Encode(expected), tagHelperOutput.Content.GetContent());
-            Assert.Equal(1, invokeCount);
+            Assert.Equal(1, invokeCount); // We expect getChildContentAsync to be invoked exactly once.
+            Assert.Equal(encoder.Encode(expected), tagHelperOutput1.Content.GetContent());
+            Assert.Equal(encoder.Encode(expected), tagHelperOutput2.Content.GetContent());
         }
 
         private static ViewContext GetViewContext()