From 70d5788077acd578064ad497ff0ec42ce6d5ee0d Mon Sep 17 00:00:00 2001
From: KANISHKMAKKAR <102965884+KANISHKMAKKAR@users.noreply.github.com>
Date: Tue, 29 Sep 2026 15:54:04 +0530
Subject: [PATCH 1/2] fix: replace busy-wait in BallThread with wait/notify
 (#2977)

---
 .../java/com/iluwatar/twin/BallThread.java    | 34 ++++++++++++++-----
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/twin/src/main/java/com/iluwatar/twin/BallThread.java b/twin/src/main/java/com/iluwatar/twin/BallThread.java
index 7768d3ebbb99..b7b99b489ad0 100644
--- a/twin/src/main/java/com/iluwatar/twin/BallThread.java
+++ b/twin/src/main/java/com/iluwatar/twin/BallThread.java
@@ -36,6 +36,8 @@ public class BallThread extends Thread {
 
   @Setter private BallItem twin;
 
+  private final Object lock = new Object();
+
   private volatile boolean isSuspended;
 
   private volatile boolean isRunning = true;
@@ -44,12 +46,18 @@ public class BallThread extends Thread {
   public void run() {
 
     while (isRunning) {
-      if (!isSuspended) {
-        twin.draw();
-        twin.move();
-      }
       try {
-        Thread.sleep(250);
+        synchronized (lock) {
+          // Wait to be notified instead of polling, so resuming takes effect immediately.
+          while (isSuspended && isRunning) {
+            lock.wait();
+          }
+        }
+        if (isRunning) {
+          twin.draw();
+          twin.move();
+          Thread.sleep(250);
+        }
       } catch (InterruptedException e) {
         throw new RuntimeException(e);
       }
@@ -57,17 +65,25 @@ public void run() {
   }
 
   public void suspendMe() {
-    isSuspended = true;
+    synchronized (lock) {
+      isSuspended = true;
+    }
     LOGGER.info("Begin to suspend BallThread");
   }
 
   public void resumeMe() {
-    isSuspended = false;
+    synchronized (lock) {
+      isSuspended = false;
+      lock.notifyAll();
+    }
     LOGGER.info("Begin to resume BallThread");
   }
 
   public void stopMe() {
-    this.isRunning = false;
-    this.isSuspended = true;
+    synchronized (lock) {
+      this.isRunning = false;
+      this.isSuspended = true;
+      lock.notifyAll();
+    }
   }
 }

From 7c10feca57f39c3493857bedb4c3437d72f62062 Mon Sep 17 00:00:00 2001
From: KANISHKMAKKAR <102965884+KANISHKMAKKAR@users.noreply.github.com>
Date: Tue, 29 Sep 2026 15:54:11 +0530
Subject: [PATCH 2/2] docs: update twin README to match BallThread fix

---
 twin/README.md | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/twin/README.md b/twin/README.md
index f6fb6923c069..d07f49d20a01 100644
--- a/twin/README.md
+++ b/twin/README.md
@@ -88,17 +88,24 @@ public class BallItem extends GameItem {
 public class BallThread extends Thread {
   @Setter
   private BallItem twin;
+  private final Object lock = new Object();
   private volatile boolean isSuspended;
   private volatile boolean isRunning = true;
 
   public void run() {
     while (isRunning) {
-      if (!isSuspended) {
-        twin.draw();
-        twin.move();
-      }
       try {
-        Thread.sleep(250);
+        synchronized (lock) {
+          // Wait to be notified instead of polling, so resuming takes effect immediately.
+          while (isSuspended && isRunning) {
+            lock.wait();
+          }
+        }
+        if (isRunning) {
+          twin.draw();
+          twin.move();
+          Thread.sleep(250);
+        }
       } catch (InterruptedException e) {
         throw new RuntimeException(e);
       }
@@ -106,18 +113,26 @@ public class BallThread extends Thread {
   }
 
   public void suspendMe() {
-    isSuspended = true;
+    synchronized (lock) {
+      isSuspended = true;
+    }
     LOGGER.info("Begin to suspend BallThread");
   }
 
   public void resumeMe() {
-    isSuspended = false;
+    synchronized (lock) {
+      isSuspended = false;
+      lock.notifyAll();
+    }
     LOGGER.info("Begin to resume BallThread");
   }
 
   public void stopMe() {
-    this.isRunning = false;
-    this.isSuspended = true;
+    synchronized (lock) {
+      this.isRunning = false;
+      this.isSuspended = true;
+      lock.notifyAll();
+    }
   }
 }
 ```