Fix race with TestApplicationErrorLogger (#26385)

BrennanConroy · web-flow · commit 60f159f4f6fa · 2020-09-28T12:28:02.000-07:00
diff --git a/src/Servers/Kestrel/shared/test/TestApplicationErrorLogger.cs b/src/Servers/Kestrel/shared/test/TestApplicationErrorLogger.cs
@@ -106,8 +106,11 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except
 
             if (_messageFilter?.Invoke(logMessage) == true)
             {
-                _messageFilterTcs.TrySetResult(logMessage);
+                var localTcs = _messageFilterTcs;
+                // need to set tcs to null before calling TrySetResult
+                // to prevent the next WaitForMessage possibly throwing for a non-null tcs
                 _messageFilterTcs = null;
+                localTcs.TrySetResult(logMessage);
             }
         }
 

Original file line number	Diff line number	Diff line change
`@@ -106,8 +106,11 @@ public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Except`
`106`	`106`
`107`	`107`	`if (_messageFilter?.Invoke(logMessage) == true)`
`108`	`108`	`{`
`109`		`- _messageFilterTcs.TrySetResult(logMessage);`
	`109`	`+ var localTcs = _messageFilterTcs;`
	`110`	`+ // need to set tcs to null before calling TrySetResult`
	`111`	`+ // to prevent the next WaitForMessage possibly throwing for a non-null tcs`
`110`	`112`	`_messageFilterTcs = null;`
	`113`	`+ localTcs.TrySetResult(logMessage);`
`111`	`114`	`}`
`112`	`115`	`}`
`113`	`116`