better exit

src/main/java/ru/lionarius/Main.java

@@ -6,6 +6,11 @@ import java.util.Scanner;
 import java.util.function.Function;
 
 public class Main {
+    /**
+     * Flag to indicate whether the application is running or not.
+     */
+    private static boolean isRunning = true;
+
     /**
      * Counter to assign unique IDs to each calculation thread.
      */
@@ -23,7 +28,7 @@ public class Main {
 
         var scanner = new Scanner(System.in);
 
-        while (true) {
+        while (isRunning) {
             System.out.println("Enter desired command (start <e>, stop <n>, await <n>, exit):");
             var input = scanner.nextLine().trim();
             var command = input.split(" ");
@@ -129,6 +134,14 @@ public class Main {
     private static void handleExitCommand() {
         System.out.println("Shutting down...");
         threads.values().forEach(CalculationThread::interrupt);
-        System.exit(0);
+
+        for (var thread : threads.values()) {
+            try {
+                thread.join();
+            } catch (InterruptedException ignored) {
+            }
+        }
+
+        isRunning = false;
     }
 }