Allow heartbeat to restart the pipe thread with only sync commands

src/StackExchange.Redis/PhysicalBridge.cs

@@ -615,7 +615,7 @@ internal void OnHeartbeat(bool ifConnectedOnly)
                                 Interlocked.Exchange(ref connectTimeoutRetryCount, 0);
                                 tmp.BridgeCouldBeNull?.ServerEndPoint?.ClearUnselectable(UnselectableFlags.DidNotRespond);
                             }
-                            int timedOutThisHeartbeat = tmp.OnBridgeHeartbeat();
+                            tmp.OnBridgeHeartbeat(out int asyncTimeoutThisHeartbeat, out int syncTimeoutThisHeartbeat);
                             int writeEverySeconds = ServerEndPoint.WriteEverySeconds;
                             bool configCheckDue = ServerEndPoint.ConfigCheckSeconds > 0 && ServerEndPoint.LastInfoReplicationCheckSecondsAgo >= ServerEndPoint.ConfigCheckSeconds;
 
@@ -664,14 +664,15 @@ internal void OnHeartbeat(bool ifConnectedOnly)
                             }
 
                             // This is an "always" check - we always want to evaluate a dead connection from a non-responsive sever regardless of the need to heartbeat above
-                            if (timedOutThisHeartbeat > 0
+                            var totalTimeoutThisHeartbeat = asyncTimeoutThisHeartbeat + syncTimeoutThisHeartbeat;
+                            if ((totalTimeoutThisHeartbeat > 0)
                                 && tmp.LastReadSecondsAgo * 1_000 > (tmp.BridgeCouldBeNull?.Multiplexer.AsyncTimeoutMilliseconds * 4))
                             {
                                 // If we've received *NOTHING* on the pipe in 4 timeouts worth of time and we're timing out commands, issue a connection failure so that we reconnect
                                 // This is meant to address the scenario we see often in Linux configs where TCP retries will happen for 15 minutes.
                                 // To us as a client, we'll see the socket as green/open/fine when writing but we'll bet getting nothing back.
                                 // Since we can't depend on the pipe to fail in that case, we want to error here based on the criteria above so we reconnect broken clients much faster.
-                                tmp.BridgeCouldBeNull?.Multiplexer.Logger?.LogWarningDeadSocketDetected(tmp.LastReadSecondsAgo, timedOutThisHeartbeat);
+                                tmp.BridgeCouldBeNull?.Multiplexer.Logger?.LogWarningDeadSocketDetected(tmp.LastReadSecondsAgo, totalTimeoutThisHeartbeat);
                                 OnDisconnected(ConnectionFailureType.SocketFailure, tmp, out _, out State oldState);
                                 tmp.Dispose(); // Cleanup the existing connection/socket if any, otherwise it will wait reading indefinitely
                             }

src/StackExchange.Redis/PhysicalConnection.cs

@@ -746,10 +746,12 @@ internal void GetStormLog(StringBuilder sb)
         /// <summary>
         /// Runs on every heartbeat for a bridge, timing out any commands that are overdue and returning an integer of how many we timed out.
         /// </summary>
-        /// <returns>How many commands were overdue and threw timeout exceptions.</returns>
-        internal int OnBridgeHeartbeat()
+        /// <param name="asyncTimeoutDetected">How many async commands were overdue and threw timeout exceptions.</param>
+        /// <param name="syncTimeoutDetected">How many sync commands were overdue. No exception are thrown for these commands here.</param>
+        internal void OnBridgeHeartbeat(out int asyncTimeoutDetected, out int syncTimeoutDetected)
         {
-            var result = 0;
+            asyncTimeoutDetected = 0;
+            syncTimeoutDetected = 0;
             var now = Environment.TickCount;
             Interlocked.Exchange(ref lastBeatTickCount, now);
 
@@ -776,7 +778,13 @@ internal int OnBridgeHeartbeat()
                                 multiplexer.OnMessageFaulted(msg, timeoutEx);
                                 msg.SetExceptionAndComplete(timeoutEx, bridge); // tell the message that it is doomed
                                 multiplexer.OnAsyncTimeout();
-                                result++;
+                                asyncTimeoutDetected++;
+                            }
+                            else
+                            {
+                                // Only count how many sync timeouts we detect here.
+                                // The actual timeout is handled in ConnectionMultiplexer.ExecuteSyncImpl().
+                                syncTimeoutDetected++;
                             }
                         }
                         else
@@ -791,7 +799,6 @@ internal int OnBridgeHeartbeat()
                     }
                 }
             }
-            return result;
         }
 
         internal void OnInternalError(Exception exception, [CallerMemberName] string? origin = null)