Fix Heartbeat logging after disposal (#47580)

Author: mconnew

src/Servers/Kestrel/Core/src/Internal/Infrastructure/Heartbeat.cs

@@ -62,17 +62,20 @@ internal void OnHeartbeat()
         }
         catch (Exception ex)
         {
-            _trace.LogError(0, ex, $"{nameof(Heartbeat)}.{nameof(OnHeartbeat)}");
+            if (!_stopped)
+            {
+                _trace.LogError(0, ex, $"{nameof(Heartbeat)}.{nameof(OnHeartbeat)}");
+            }
         }
     }
 
     private void TimerLoop()
     {
+        Thread.Sleep(_interval);
         while (!_stopped)
         {
-            Thread.Sleep(_interval);
-
             OnHeartbeat();
+            Thread.Sleep(_interval);
         }
     }
 

src/Servers/Kestrel/Core/test/HeartbeatTests.cs

@@ -123,4 +123,20 @@ public void ExceptionFromHeartbeatHandlerIsLoggedAsError()
 
         Assert.Equal(ex, TestSink.Writes.Single(message => message.LogLevel == LogLevel.Error).Exception);
     }
+
+    [Fact]
+    public void ExceptionFromHeartbeatHandlerIsNotLoggedIfDisposed()
+    {
+        var systemClock = new MockSystemClock();
+        var heartbeatHandler = new Mock<IHeartbeatHandler>();
+        var debugger = new Mock<IDebugger>();
+        var kestrelTrace = new KestrelTrace(LoggerFactory);
+        var ex = new Exception();
+        heartbeatHandler.Setup(h => h.OnHeartbeat(systemClock.UtcNow)).Throws(ex);
+        debugger.Setup(d => d.IsAttached).Returns(true);
+        var heartbeat = new Heartbeat(new[] { heartbeatHandler.Object }, systemClock, debugger.Object, kestrelTrace);
+        heartbeat.Dispose();
+        heartbeat.OnHeartbeat();
+        Assert.Empty(TestSink.Writes);
+    }
 }