BAEL-3139: Moved code to a new project core-java-concurrency-2 (#7778)

core-java-modules/core-java-concurrency-2/.gitignore

@@ -0,0 +1,26 @@
+*.class
+
+0.*
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+.resourceCache
+
+# Packaged files #
+*.jar
+*.war
+*.ear
+
+# Files generated by integration tests
+*.txt
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-modules/core-java-concurrency-2/README.md

@@ -0,0 +1,7 @@
+=========
+
+## Core Java Concurrency 2 Examples
+
+### Relevant Articles: 
+- [Using a Mutex Object in Java](https://www.baeldung.com/java-mutex)
+

core-java-modules/core-java-concurrency-2/pom.xml

@@ -0,0 +1,27 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-concurrency-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-concurrency-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <build>
+        <finalName>core-java-concurrency-2</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+</project>

core-java-modules/core-java-concurrency-2/src/main/java/com/baeldung/concurrent/mutex/SequenceGenerator.java

@@ -0,0 +1,12 @@
+package com.baeldung.concurrent.mutex;
+
+public class SequenceGenerator {
+
+    private int currentValue = 0;
+
+    public int getNextSequence() {
+        currentValue = currentValue + 1;
+        return currentValue;
+    }
+
+}

core-java-modules/core-java-concurrency-2/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingMonitor.java

@@ -0,0 +1,19 @@
+package com.baeldung.concurrent.mutex;
+
+import com.google.common.util.concurrent.Monitor;
+
+public class SequenceGeneratorUsingMonitor extends SequenceGenerator {
+
+    private Monitor mutex = new Monitor();
+
+    @Override
+    public int getNextSequence() {
+        mutex.enter();
+        try {
+            return super.getNextSequence();
+        } finally {
+            mutex.leave();
+        }
+    }
+
+}

core-java-modules/core-java-concurrency-2/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingReentrantLock.java

@@ -0,0 +1,19 @@
+package com.baeldung.concurrent.mutex;
+
+import java.util.concurrent.locks.ReentrantLock;
+
+public class SequenceGeneratorUsingReentrantLock extends SequenceGenerator {
+
+    private ReentrantLock mutex = new ReentrantLock();
+
+    @Override
+    public int getNextSequence() {
+        try {
+            mutex.lock();
+            return super.getNextSequence();
+        } finally {
+            mutex.unlock();
+        }
+    }
+
+}

core-java-modules/core-java-concurrency-2/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingSemaphore.java

@@ -0,0 +1,21 @@
+package com.baeldung.concurrent.mutex;
+
+import java.util.concurrent.Semaphore;
+
+public class SequenceGeneratorUsingSemaphore extends SequenceGenerator {
+
+    private Semaphore mutex = new Semaphore(1);
+
+    @Override
+    public int getNextSequence() {
+        try {
+            mutex.acquire();
+            return super.getNextSequence();
+        } catch (InterruptedException e) {
+            throw new RuntimeException("Exception in critical section.", e);
+        } finally {
+            mutex.release();
+        }
+    }
+
+}

core-java-modules/core-java-concurrency-2/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingSynchronizedBlock.java

@@ -0,0 +1,14 @@
+package com.baeldung.concurrent.mutex;
+
+public class SequenceGeneratorUsingSynchronizedBlock extends SequenceGenerator {
+
+    private Object mutex = new Object();
+
+    @Override
+    public int getNextSequence() {
+        synchronized (mutex) {
+            return super.getNextSequence();
+        }
+    }
+
+}

core-java-modules/core-java-concurrency-2/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingSynchronizedMethod.java

@@ -0,0 +1,10 @@
+package com.baeldung.concurrent.mutex;
+
+public class SequenceGeneratorUsingSynchronizedMethod extends SequenceGenerator {
+
+    @Override
+    public synchronized int getNextSequence() {
+        return super.getNextSequence();
+    }
+
+}

core-java-modules/core-java-concurrency-2/src/main/resources/logback.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <logger name="org.springframework" level="WARN" />
+    <logger name="org.springframework.transaction" level="WARN" />
+
+    <!-- in order to debug some marshalling issues, this needs to be TRACE -->
+    <logger name="org.springframework.web.servlet.mvc" level="WARN" />
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

core-java-modules/core-java-concurrency-2/src/test/java/com/baeldung/concurrent/mutex/MutexUnitTest.java

@@ -0,0 +1,80 @@
+package com.baeldung.concurrent.mutex;
+
+import java.util.ArrayList;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class MutexUnitTest {
+
+    // @Test
+    // This test verifies the race condition use case, it may pass or fail based on execution environment
+    // Uncomment @Test to run it
+    public void givenUnsafeSequenceGenerator_whenRaceCondition_thenUnexpectedBehavior() throws Exception {
+        int count = 1000;
+        Set<Integer> uniqueSequences = getUniqueSequences(new SequenceGenerator(), count);
+        Assert.assertNotEquals(count, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingSynchronizedMethod_whenRaceCondition_thenSuccess() throws Exception {
+        int count = 1000;
+        Set<Integer> uniqueSequences = getUniqueSequences(new SequenceGeneratorUsingSynchronizedMethod(), count);
+        Assert.assertEquals(count, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingSynchronizedBlock_whenRaceCondition_thenSuccess() throws Exception {
+        int count = 1000;
+        Set<Integer> uniqueSequences = getUniqueSequences(new SequenceGeneratorUsingSynchronizedBlock(), count);
+        Assert.assertEquals(count, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingReentrantLock_whenRaceCondition_thenSuccess() throws Exception {
+        int count = 1000;
+        Set<Integer> uniqueSequences = getUniqueSequences(new SequenceGeneratorUsingReentrantLock(), count);
+        Assert.assertEquals(count, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingSemaphore_whenRaceCondition_thenSuccess() throws Exception {
+        int count = 1000;
+        Set<Integer> uniqueSequences = getUniqueSequences(new SequenceGeneratorUsingSemaphore(), count);
+        Assert.assertEquals(count, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingMonitor_whenRaceCondition_thenSuccess() throws Exception {
+        int count = 1000;
+        Set<Integer> uniqueSequences = getUniqueSequences(new SequenceGeneratorUsingMonitor(), count);
+        Assert.assertEquals(count, uniqueSequences.size());
+    }
+
+    private Set<Integer> getUniqueSequences(SequenceGenerator generator, int count) throws Exception {
+        ExecutorService executor = Executors.newFixedThreadPool(3);
+        Set<Integer> uniqueSequences = new LinkedHashSet<>();
+        List<Future<Integer>> futures = new ArrayList<>();
+
+        for (int i = 0; i < count; i++) {
+            futures.add(executor.submit(generator::getNextSequence));
+        }
+
+        for (Future<Integer> future : futures) {
+            uniqueSequences.add(future.get());
+        }
+
+        executor.awaitTermination(1, TimeUnit.SECONDS);
+        executor.shutdown();
+
+        return uniqueSequences;
+    }
+
+}

core-java-modules/core-java-concurrency-2/src/test/resources/.gitignore

@@ -0,0 +1,13 @@
+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear