[JAVA-22519] Move articles from generic libraries module to specific library modules (#15416)

libraries-concurrency/src/main/java/com/baeldung/jctools/MpmcBenchmark.java

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+package com.baeldung.jctools;
+
+import java.util.Queue;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.TimeUnit;
+
+import org.jctools.queues.MpmcArrayQueue;
+import org.jctools.queues.atomic.MpmcAtomicArrayQueue;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Group;
+import org.openjdk.jmh.annotations.GroupThreads;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.infra.Control;
+
+@BenchmarkMode(Mode.SampleTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Fork(1)
+@Warmup(iterations = 1)
+@Measurement(iterations = 3)
+@State(Scope.Group)
+public class MpmcBenchmark {
+
+    public static final String PARAM_UNSAFE = "MpmcArrayQueue";
+    public static final String PARAM_AFU = "MpmcAtomicArrayQueue";
+    public static final String PARAM_JDK = "ArrayBlockingQueue";
+
+    public static final int PRODUCER_THREADS_NUMBER = 32;
+    public static final int CONSUMER_THREADS_NUMBER = 32;
+
+    public static final String GROUP_NAME = "MyGroup";
+
+    public static final int CAPACITY = 128;
+
+    @Param({PARAM_UNSAFE, PARAM_AFU, PARAM_JDK})
+    public volatile String implementation;
+
+    public volatile Queue<Long> queue;
+
+    @Setup(Level.Trial)
+    public void setUp() {
+        switch (implementation) {
+            case PARAM_UNSAFE:
+                queue = new MpmcArrayQueue<>(CAPACITY);
+                break;
+            case PARAM_AFU:
+                queue = new MpmcAtomicArrayQueue<>(CAPACITY);
+                break;
+            case PARAM_JDK:
+                queue = new ArrayBlockingQueue<>(CAPACITY);
+                break;
+            default:
+                throw new UnsupportedOperationException("Unsupported implementation " + implementation);
+        }
+    }
+
+
+    @Benchmark
+    @Group(GROUP_NAME)
+    @GroupThreads(PRODUCER_THREADS_NUMBER)
+    public void write(Control control) {
+        //noinspection StatementWithEmptyBody
+        while (!control.stopMeasurement && !queue.offer(1L)) {
+            // Is intentionally left blank
+        }
+    }
+
+    @Benchmark
+    @Group(GROUP_NAME)
+    @GroupThreads(CONSUMER_THREADS_NUMBER)
+    public void read(Control control) {
+        //noinspection StatementWithEmptyBody
+        while (!control.stopMeasurement && queue.poll() == null) {
+            // Is intentionally left blank
+        }
+    }
+}

libraries-concurrency/src/main/java/com/baeldung/jctools/README.md

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+## How to build and run the JMH benchmark
+
+Execute the following from the project's root:  
+```bash
+mvn clean install
+java -jar ./target/benchmarks.jar MpmcBenchmark -si true
+```

libraries-concurrency/src/test/java/com/baeldung/jctools/JCToolsUnitTest.java

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+package com.baeldung.jctools;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import org.assertj.core.api.Assertions;
+import org.jctools.queues.SpscArrayQueue;
+import org.jctools.queues.SpscChunkedArrayQueue;
+import org.junit.Test;
+
+public class JCToolsUnitTest {
+
+    @Test
+    public void givenMultipleProducers_whenSpscQueueUsed_thenNoWarningOccurs() throws InterruptedException {
+        SpscArrayQueue<Integer> queue = new SpscArrayQueue<Integer>(2);
+
+        Thread producer1 = new Thread(() -> {
+            queue.offer(1);
+        });
+        producer1.start();
+        producer1.join();
+
+        Thread producer2 = new Thread(() -> {
+            queue.offer(2);
+        });
+        producer2.start();
+        producer2.join();
+
+        Set<Integer> fromQueue = new HashSet<>();
+        Thread consumer = new Thread(() -> queue.drain(fromQueue::add));
+        consumer.start();
+        consumer.join();
+
+        assertThat(fromQueue).containsOnly(1, 2);
+    }
+
+    @Test
+    public void whenQueueIsFull_thenNoMoreElementsCanBeAdded() throws InterruptedException {
+        SpscChunkedArrayQueue<Integer> queue = new SpscChunkedArrayQueue<>(8, 16);
+        Assertions.assertThat(queue.capacity()).isEqualTo(16);
+
+        CountDownLatch startConsuming = new CountDownLatch(1);
+        CountDownLatch awakeProducer = new CountDownLatch(1);
+        AtomicReference<Throwable> error = new AtomicReference<>();
+        Thread producer = new Thread(() -> {
+            IntStream.range(0, queue.capacity()).forEach(i -> {
+                Assertions.assertThat(queue.offer(i)).isTrue();
+            });
+            Assertions.assertThat(queue.offer(queue.capacity())).isFalse();
+            startConsuming.countDown();
+            try {
+                awakeProducer.await();
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+
+            Assertions.assertThat(queue.offer(queue.capacity())).isTrue();
+        });
+        producer.setUncaughtExceptionHandler((t, e) -> {
+            error.set(e);
+            startConsuming.countDown();
+        });
+        producer.start();
+
+        startConsuming.await();
+
+        if (error.get() != null) {
+            fail("Producer's assertion failed", error.get());
+        }
+
+        Set<Integer> fromQueue = new HashSet<>();
+        queue.drain(fromQueue::add);
+        awakeProducer.countDown();
+        producer.join();
+        queue.drain(fromQueue::add);
+
+        assertThat(fromQueue).containsAll(IntStream.range(0, 17).boxed().collect(Collectors.toSet()));
+    }
+}