CalculatorServiceHandler.patch

 import com.example.calculator.protocol.TOperation;
+import com.google.common.util.concurrent.*;
 import org.springframework.stereotype.Component;
 
 import com.example.calculator.service.CalculatorService;
 import org.springframework.beans.factory.annotation.Autowired;
 
+import java.util.concurrent.*;
+
 @Component
 public class CalculatorServiceHandler implements TCalculatorService {
 
     @Autowired
     CalculatorService calculatorService;
 
+    ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(10);
+
     @Override
-    public int calculate(int num1, int num2, TOperation op) throws TDivisionByZeroException {
+    public ListenableFuture<Integer> calculate(int num1, int num2, TOperation op) throws TDivisionByZeroException {
+        return JdkFutureAdapters.listenInPoolThread(
+                scheduledExecutorService.schedule(() -> {
         switch(op) {
             case ADD:
                 return calculatorService.add(num1, num2);
@@ -32,5 +40,7 @@
             default:
                 throw new IllegalArgumentException("Unknown operation " + op);
         }
+                }, 2, TimeUnit.SECONDS)
+        );
     }
 }