From 163056b1ca75f656c02ef282689424ace59cc485 Mon Sep 17 00:00:00 2001
From: timis1 <12120641+timis1@users.noreply.github.com>
Date: Wed, 22 Mar 2023 10:26:22 +0200
Subject: [PATCH] =?UTF-8?q?JAVA-18228=20Potential=20issue=20in=20"Producer?=
 =?UTF-8?q?-Consumer=20Problem=20With=20Example=E2=80=A6=20(#13582)?=
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JAVA-18228 Potential issue in "Producer-Consumer Problem With Example in Java" article
---
 .../baeldung/producerconsumer/Consumer.java   | 31 +++++++++----------
 .../baeldung/producerconsumer/DataQueue.java  |  2 ++
 .../baeldung/producerconsumer/Producer.java   | 30 +++++++++---------
 3 files changed, 32 insertions(+), 31 deletions(-)

diff --git a/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Consumer.java b/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Consumer.java
index 5a059b74df..9bbcbb923c 100644
--- a/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Consumer.java
+++ b/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Consumer.java
@@ -2,11 +2,9 @@ package com.baeldung.producerconsumer;
 
 public class Consumer implements Runnable {
     private final DataQueue dataQueue;
-    private volatile boolean runFlag;
 
     public Consumer(DataQueue dataQueue) {
         this.dataQueue = dataQueue;
-        runFlag = true;
     }
 
     @Override
@@ -15,22 +13,23 @@ public class Consumer implements Runnable {
     }
 
     public void consume() {
-        while (runFlag) {
-            Message message;
-            if (dataQueue.isEmpty()) {
-                try {
-                    dataQueue.waitOnEmpty();
-                } catch (InterruptedException e) {
-                    e.printStackTrace();
+        while (dataQueue.runFlag) {
+            synchronized (this) {
+                while (dataQueue.isEmpty() && dataQueue.runFlag) {
+                    try {
+                        dataQueue.waitOnEmpty();
+                    } catch (InterruptedException e) {
+                        e.printStackTrace();
+                        break;
+                    }
+                }
+                if (!dataQueue.runFlag) {
                     break;
                 }
+                Message message = dataQueue.remove();
+                dataQueue.notifyAllForFull();
+                useMessage(message);
             }
-            if (!runFlag) {
-                break;
-            }
-            message = dataQueue.remove();
-            dataQueue.notifyAllForFull();
-            useMessage(message);
         }
         System.out.println("Consumer Stopped");
     }
@@ -45,7 +44,7 @@ public class Consumer implements Runnable {
     }
 
     public void stop() {
-        runFlag = false;
+        dataQueue.runFlag = false;
         dataQueue.notifyAllForEmpty();
     }
 }
diff --git a/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/DataQueue.java b/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/DataQueue.java
index 6ab4fa2bc3..8867ddeb63 100644
--- a/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/DataQueue.java
+++ b/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/DataQueue.java
@@ -9,6 +9,8 @@ public class DataQueue {
     private final Object FULL_QUEUE = new Object();
     private final Object EMPTY_QUEUE = new Object();
 
+    public boolean runFlag = true;
+
     DataQueue(int maxSize) {
         this.maxSize = maxSize;
     }
diff --git a/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Producer.java b/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Producer.java
index 80d693bd97..04ad39f26e 100644
--- a/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Producer.java
+++ b/core-java-modules/core-java-concurrency-advanced-4/src/main/java/com/baeldung/producerconsumer/Producer.java
@@ -2,13 +2,11 @@ package com.baeldung.producerconsumer;
 
 public class Producer implements Runnable {
     private final DataQueue dataQueue;
-    private volatile boolean runFlag;
 
     private static int idSequence = 0;
 
     public Producer(DataQueue dataQueue) {
         this.dataQueue = dataQueue;
-        runFlag = true;
     }
 
     @Override
@@ -17,21 +15,23 @@ public class Producer implements Runnable {
     }
 
     public void produce() {
-        while (runFlag) {
-            Message message = generateMessage();
-            while (dataQueue.isFull()) {
-                try {
-                    dataQueue.waitOnFull();
-                } catch (InterruptedException e) {
-                    e.printStackTrace();
+        while (dataQueue.runFlag) {
+            synchronized (this) {
+                while (dataQueue.isFull() && dataQueue.runFlag) {
+                    try {
+                        dataQueue.waitOnFull();
+                    } catch (InterruptedException e) {
+                        e.printStackTrace();
+                        break;
+                    }
+                }
+                if (!dataQueue.runFlag) {
                     break;
                 }
+                Message message = generateMessage();
+                dataQueue.add(message);
+                dataQueue.notifyAllForEmpty();
             }
-            if (!runFlag) {
-                break;
-            }
-            dataQueue.add(message);
-            dataQueue.notifyAllForEmpty();
         }
         System.out.println("Producer Stopped");
     }
@@ -47,7 +47,7 @@ public class Producer implements Runnable {
     }
 
     public void stop() {
-        runFlag = false;
+        dataQueue.runFlag = false;
         dataQueue.notifyAllForFull();
     }
 }