diff --git a/study/src/main/resources/application.yml b/study/src/main/resources/application.yml
index 8b74bdfd88..c566b7ab5c 100644
--- a/study/src/main/resources/application.yml
+++ b/study/src/main/resources/application.yml
@@ -3,8 +3,8 @@ handlebars:
 
 server:
   tomcat:
-    accept-count: 1
-    max-connections: 1
+    accept-count: 0
+    max-connections: 2
     threads:
       min-spare: 2
       max: 2
diff --git a/study/src/test/java/thread/stage0/SynchronizationTest.java b/study/src/test/java/thread/stage0/SynchronizationTest.java
index 0333c18e3b..b463c2b984 100644
--- a/study/src/test/java/thread/stage0/SynchronizationTest.java
+++ b/study/src/test/java/thread/stage0/SynchronizationTest.java
@@ -41,7 +41,7 @@ private static final class SynchronizedMethods {
 
         private int sum = 0;
 
-        public void calculate() {
+        public synchronized void calculate() {
             setSum(getSum() + 1);
         }
 
diff --git a/study/src/test/java/thread/stage0/ThreadPoolsTest.java b/study/src/test/java/thread/stage0/ThreadPoolsTest.java
index 238611ebfe..03efdabc8d 100644
--- a/study/src/test/java/thread/stage0/ThreadPoolsTest.java
+++ b/study/src/test/java/thread/stage0/ThreadPoolsTest.java
@@ -31,8 +31,8 @@ void testNewFixedThreadPool() {
         executor.submit(logWithSleep("hello fixed thread pools"));
 
         // 올바른 값으로 바꿔서 테스트를 통과시키자.
-        final int expectedPoolSize = 0;
-        final int expectedQueueSize = 0;
+        final int expectedPoolSize = 2;
+        final int expectedQueueSize = 1;
 
         assertThat(expectedPoolSize).isEqualTo(executor.getPoolSize());
         assertThat(expectedQueueSize).isEqualTo(executor.getQueue().size());
@@ -46,7 +46,7 @@ void testNewCachedThreadPool() {
         executor.submit(logWithSleep("hello cached thread pools"));
 
         // 올바른 값으로 바꿔서 테스트를 통과시키자.
-        final int expectedPoolSize = 0;
+        final int expectedPoolSize = 3;
         final int expectedQueueSize = 0;
 
         assertThat(expectedPoolSize).isEqualTo(executor.getPoolSize());
diff --git a/study/src/test/java/thread/stage2/AppTest.java b/study/src/test/java/thread/stage2/AppTest.java
index e253c4a249..cfc8e27a3b 100644
--- a/study/src/test/java/thread/stage2/AppTest.java
+++ b/study/src/test/java/thread/stage2/AppTest.java
@@ -1,5 +1,6 @@
 package thread.stage2;
 
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import java.net.http.HttpResponse;
@@ -21,6 +22,7 @@ class AppTest {
      * - http call count
      * - 테스트 결과값
      */
+    @Disabled // 테스트를 실행시키기 위해서 thred.stage2.App을 실행하고 @Disabled를 제거하세요.
     @Test
     void test() throws Exception {
         final var NUMBER_OF_THREAD = 10;
diff --git a/tomcat/src/main/java/org/apache/catalina/connector/Connector.java b/tomcat/src/main/java/org/apache/catalina/connector/Connector.java
index 3b2c4dda7c..a1b6a277fc 100644
--- a/tomcat/src/main/java/org/apache/catalina/connector/Connector.java
+++ b/tomcat/src/main/java/org/apache/catalina/connector/Connector.java
@@ -1,13 +1,14 @@
 package org.apache.catalina.connector;
 
-import org.apache.coyote.http11.Http11Processor;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.net.ServerSocket;
 import java.net.Socket;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import org.apache.coyote.http11.Http11Processor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 public class Connector implements Runnable {
 
@@ -15,17 +16,20 @@ public class Connector implements Runnable {
 
     private static final int DEFAULT_PORT = 8080;
     private static final int DEFAULT_ACCEPT_COUNT = 100;
+    private static final int DEFAULT_MAX_THREADS = 250;
 
     private final ServerSocket serverSocket;
+    private final ExecutorService executorService;
     private boolean stopped;
 
     public Connector() {
-        this(DEFAULT_PORT, DEFAULT_ACCEPT_COUNT);
+        this(DEFAULT_PORT, DEFAULT_ACCEPT_COUNT, DEFAULT_MAX_THREADS);
     }
 
-    public Connector(final int port, final int acceptCount) {
+    public Connector(final int port, final int acceptCount, final int maxThreads) {
         this.serverSocket = createServerSocket(port, acceptCount);
         this.stopped = false;
+        this.executorService = Executors.newFixedThreadPool(maxThreads);
     }
 
     private ServerSocket createServerSocket(final int port, final int acceptCount) {
@@ -67,13 +71,14 @@ private void process(final Socket connection) {
             return;
         }
         var processor = new Http11Processor(connection);
-        new Thread(processor).start();
+        executorService.submit(processor);
     }
 
     public void stop() {
         stopped = true;
         try {
             serverSocket.close();
+            executorService.shutdown();
         } catch (IOException e) {
             log.error(e.getMessage(), e);
         }
diff --git a/tomcat/src/main/java/org/apache/catalina/session/SessionManager.java b/tomcat/src/main/java/org/apache/catalina/session/SessionManager.java
index 4c5a27a0d7..0c2eb4706e 100644
--- a/tomcat/src/main/java/org/apache/catalina/session/SessionManager.java
+++ b/tomcat/src/main/java/org/apache/catalina/session/SessionManager.java
@@ -1,7 +1,7 @@
 package org.apache.catalina.session;
 
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import lombok.AccessLevel;
 import lombok.NoArgsConstructor;
 
@@ -9,7 +9,7 @@
 public class SessionManager {
 
     private static final SessionManager INSTANCE = new SessionManager();
-    private static final Map<String, Session> SESSIONS = new HashMap<>();
+    private static final Map<String, Session> SESSIONS = new ConcurrentHashMap<>();
 
     public static SessionManager getInstance() {
         return INSTANCE;