BAEL-519 Introduction to LMAX Disruptor (#948)

* BAL-36 File size api in java and apache commons IO

* BAEL-282 grep in java - fixes after code review

* BAEL-519 Added support for disruptor library

* BAEL-519 Added support for disruptor library

* BAEL-519 Added support for disruptor library

* BAEL-519 Added support for disruptor library

* BAEL-519 Added support for disruptor library

* BAEL-519 Added support for disruptor library

* BAEL-519 Added support for disruptor

* BAEL-519 Moved all supporting classes to main source

* BAEL-519 Moved all supporting classes to main source

* BAEL-519 Moved asserts and test classes in test folder.

* BAEL-519 moved test related producer and consumer to src.

* BAEL-586 Guide to Guava BiMap.

* BAEL-587 formatted code.

* BAEL-519 LMAX Disruptor

* BAEL-587 resolved merge

* BAEL-587 Resolved merge

* BAEL-519 Removed disruptor link.

* BAEL-519 Reverted Guava changes

core-java/README.md

@@ -52,4 +52,4 @@
 - [URL Encoding and Decoding in Java](http://www.baeldung.com/java-url-encoding-decoding)
 - [Calculate the Size of a File in Java](http://www.baeldung.com/java-file-size)
 - [The Basics of Java Generics](http://www.baeldung.com/java-generics)
-- [The Traveling Salesman Problem in Java](http://www.baeldung.com/java-simulated-annealing-for-traveling-salesman)
+- [The Traveling Salesman Problem in Java](http://www.baeldung.com/java-simulated-annealing-for-traveling-salesman)

core-java/pom.xml

@@ -63,6 +63,12 @@
             <artifactId>grep4j</artifactId>
             <version>${grep4j.version}</version>
         </dependency>
+        
+        <dependency>
+            <groupId>com.lmax</groupId>
+            <artifactId>disruptor</artifactId>
+            <version>${disruptor.version}</version>
+        </dependency>
         <!-- web -->
 
         <!-- marshalling -->
@@ -363,6 +369,7 @@
         <unix4j.version>0.4</unix4j.version>
         <grep4j.version>1.8.7</grep4j.version>
         <lombok.version>1.16.12</lombok.version>
+        <disruptor.version>3.3.6</disruptor.version>
 
         <!-- testing -->
         <org.hamcrest.version>1.3</org.hamcrest.version>

core-java/src/main/java/com/baeldung/disruptor/DelayedMultiEventProducer.java

@@ -0,0 +1,34 @@
+package com.baeldung.disruptor;
+
+import com.lmax.disruptor.RingBuffer;
+
+public class DelayedMultiEventProducer implements EventProducer {
+
+    @Override
+    public void startProducing(final RingBuffer<ValueEvent> ringBuffer, final int count) {
+        final Runnable simpleProducer = () -> produce(ringBuffer, count, false);
+        final Runnable delayedProducer = () -> produce(ringBuffer, count, true);
+        new Thread(simpleProducer).start();
+        new Thread(delayedProducer).start();
+    }
+
+    private void produce(final RingBuffer<ValueEvent> ringBuffer, final int count, final boolean addDelay) {
+        for (int i = 0; i < count; i++) {
+            final long seq = ringBuffer.next();
+            final ValueEvent valueEvent = ringBuffer.get(seq);
+            valueEvent.setValue(i);
+            ringBuffer.publish(seq);
+            if (addDelay) {
+                addDelay();
+            }
+        }
+    }
+
+    private void addDelay() {
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException interruptedException) {
+            // No-Op lets swallow it
+        }
+    }
+}

core-java/src/main/java/com/baeldung/disruptor/EventConsumer.java

@@ -0,0 +1,13 @@
+package com.baeldung.disruptor;
+
+import com.lmax.disruptor.EventHandler;
+
+/**
+ * Consumer that consumes event from ring buffer. 
+ */
+public interface EventConsumer {
+    /**
+     * One or more event handler to handle event from ring buffer. 
+     */
+    public EventHandler<ValueEvent>[] getEventHandler();
+}

core-java/src/main/java/com/baeldung/disruptor/EventProducer.java

@@ -0,0 +1,15 @@
+package com.baeldung.disruptor;
+
+import com.lmax.disruptor.RingBuffer;
+
+/**
+ * Producer that produces event for ring buffer.
+ */
+public interface EventProducer {
+    /**
+     * Start the producer that would start producing the values.
+     * @param ringBuffer
+     * @param count
+     */
+    public void startProducing(final RingBuffer<ValueEvent> ringBuffer, final int count);
+}

core-java/src/main/java/com/baeldung/disruptor/MultiEventPrintConsumer.java

@@ -0,0 +1,23 @@
+package com.baeldung.disruptor;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.lmax.disruptor.EventHandler;
+
+public class MultiEventPrintConsumer implements EventConsumer {
+
+    private final Logger logger = LoggerFactory.getLogger(this.getClass());
+    
+    @Override
+    @SuppressWarnings("unchecked")
+    public EventHandler<ValueEvent>[] getEventHandler() {
+        final EventHandler<ValueEvent> eventHandler = (event, sequence, endOfBatch) -> print(event.getValue(), sequence);
+        final EventHandler<ValueEvent> otherEventHandler = (event, sequence, endOfBatch) -> print(event.getValue(), sequence);
+        return new EventHandler[] { eventHandler, otherEventHandler };
+    }
+
+    private void print(final int id, final long sequenceId) {
+        logger.info("Id is " + id + " sequence id that was used is " + sequenceId);
+    }
+}

core-java/src/main/java/com/baeldung/disruptor/SingleEventPrintConsumer.java

@@ -0,0 +1,22 @@
+package com.baeldung.disruptor;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.lmax.disruptor.EventHandler;
+
+public class SingleEventPrintConsumer implements EventConsumer {
+
+    private final Logger logger = LoggerFactory.getLogger(this.getClass());
+    
+    @Override
+    @SuppressWarnings("unchecked")
+    public EventHandler<ValueEvent>[] getEventHandler() {
+        final EventHandler<ValueEvent> eventHandler = (event, sequence, endOfBatch) -> print(event.getValue(), sequence);
+        return new EventHandler[] { eventHandler };
+    }
+
+    private void print(final int id, final long sequenceId) {
+        logger.info("Id is " + id + " sequence id that was used is " + sequenceId);
+    }
+}

core-java/src/main/java/com/baeldung/disruptor/SingleEventProducer.java

@@ -0,0 +1,22 @@
+package com.baeldung.disruptor;
+
+import com.lmax.disruptor.RingBuffer;
+
+public class SingleEventProducer implements EventProducer {
+
+    @Override
+    public void startProducing(RingBuffer<ValueEvent> ringBuffer, int count) {
+        final Runnable producer = () -> produce(ringBuffer, count);
+        new Thread(producer).start();
+    }
+
+    private void produce(final RingBuffer<ValueEvent> ringBuffer, final int count) {
+        for (int i = 0; i < count; i++) {
+            final long seq = ringBuffer.next();
+            final ValueEvent valueEvent = ringBuffer.get(seq);
+            valueEvent.setValue(i);
+            ringBuffer.publish(seq);
+        }
+    }
+
+}

core-java/src/main/java/com/baeldung/disruptor/ValueEvent.java

@@ -0,0 +1,25 @@
+package com.baeldung.disruptor;
+
+import org.apache.commons.lang3.builder.ToStringBuilder;
+
+import com.lmax.disruptor.EventFactory;
+
+public final class ValueEvent {
+
+    private int value;
+
+    public int getValue() {
+        return value;
+    }
+
+    public void setValue(int value) {
+        this.value = value;
+    }
+
+    public final static EventFactory<ValueEvent> EVENT_FACTORY = () -> new ValueEvent();
+
+    @Override
+    public String toString() {
+        return ToStringBuilder.reflectionToString(this);
+    }
+}

core-java/src/test/java/com/baeldung/disruptor/DisruptorTest.java

@@ -0,0 +1,83 @@
+package com.baeldung.disruptor;
+
+import java.util.concurrent.ThreadFactory;
+import org.junit.Before;
+import org.junit.Test;
+import com.lmax.disruptor.BusySpinWaitStrategy;
+import com.lmax.disruptor.RingBuffer;
+import com.lmax.disruptor.WaitStrategy;
+import com.lmax.disruptor.dsl.Disruptor;
+import com.lmax.disruptor.dsl.ProducerType;
+import com.lmax.disruptor.util.DaemonThreadFactory;
+
+public class DisruptorTest {
+    private Disruptor<ValueEvent> disruptor;
+    private WaitStrategy waitStrategy;
+
+    @Before
+    public void setUp() throws Exception {
+        waitStrategy = new BusySpinWaitStrategy();
+    }
+
+    private void createDisruptor(final ProducerType producerType, final EventConsumer eventConsumer) {
+        final ThreadFactory threadFactory = DaemonThreadFactory.INSTANCE;
+        disruptor = new Disruptor<ValueEvent>(ValueEvent.EVENT_FACTORY, 16, threadFactory, producerType, waitStrategy);
+        disruptor.handleEventsWith(eventConsumer.getEventHandler());
+    }
+
+    private void startProducing(final RingBuffer<ValueEvent> ringBuffer, final int count, final EventProducer eventProducer) {
+        eventProducer.startProducing(ringBuffer, count);
+    }
+
+    @Test
+    public void whenMultipleProducerSingleConsumer_thenOutputInFifoOrder() {
+        final EventConsumer eventConsumer = new SingleEventPrintConsumer();
+        final EventProducer eventProducer = new DelayedMultiEventProducer();
+        createDisruptor(ProducerType.MULTI, eventConsumer);
+        final RingBuffer<ValueEvent> ringBuffer = disruptor.start();
+
+        startProducing(ringBuffer, 32, eventProducer);
+
+        disruptor.halt();
+        disruptor.shutdown();
+    }
+
+    @Test
+    public void whenSingleProducerSingleConsumer_thenOutputInFifoOrder() {
+        final EventConsumer eventConsumer = new SingleEventConsumer();
+        final EventProducer eventProducer = new SingleEventProducer();
+        createDisruptor(ProducerType.SINGLE, eventConsumer);
+        final RingBuffer<ValueEvent> ringBuffer = disruptor.start();
+
+        startProducing(ringBuffer, 32, eventProducer);
+
+        disruptor.halt();
+        disruptor.shutdown();
+    }
+
+    @Test
+    public void whenSingleProducerMultipleConsumer_thenOutputInFifoOrder() {
+        final EventConsumer eventConsumer = new MultiEventConsumer();
+        final EventProducer eventProducer = new SingleEventProducer();
+        createDisruptor(ProducerType.SINGLE, eventConsumer);
+        final RingBuffer<ValueEvent> ringBuffer = disruptor.start();
+
+        startProducing(ringBuffer, 32, eventProducer);
+
+        disruptor.halt();
+        disruptor.shutdown();
+    }
+
+    @Test
+    public void whenMultipleProducerMultipleConsumer_thenOutputInFifoOrder() {
+        final EventConsumer eventConsumer = new MultiEventPrintConsumer();
+        final EventProducer eventProducer = new DelayedMultiEventProducer();
+        createDisruptor(ProducerType.MULTI, eventConsumer);
+        final RingBuffer<ValueEvent> ringBuffer = disruptor.start();
+
+        startProducing(ringBuffer, 32, eventProducer);
+
+        disruptor.halt();
+        disruptor.shutdown();
+    }
+}

core-java/src/test/java/com/baeldung/disruptor/MultiEventConsumer.java

@@ -0,0 +1,27 @@
+package com.baeldung.disruptor;
+
+import static org.junit.Assert.assertEquals;
+
+import com.lmax.disruptor.EventHandler;
+
+public class MultiEventConsumer implements EventConsumer {
+
+    private int expectedValue = -1;
+    private int otherExpectedValue = -1;
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public EventHandler<ValueEvent>[] getEventHandler() {
+        final EventHandler<ValueEvent> eventHandler = (event, sequence, endOfBatch) -> assertExpectedValue(event.getValue());
+        final EventHandler<ValueEvent> otherEventHandler = (event, sequence, endOfBatch) -> assertOtherExpectedValue(event.getValue());
+        return new EventHandler[] { eventHandler, otherEventHandler };
+    }
+
+    private void assertExpectedValue(final int id) {
+        assertEquals(++expectedValue, id);
+    }
+
+    private void assertOtherExpectedValue(final int id) {
+        assertEquals(++otherExpectedValue, id);
+    }
+}

core-java/src/test/java/com/baeldung/disruptor/SingleEventConsumer.java

@@ -0,0 +1,21 @@
+package com.baeldung.disruptor;
+
+import static org.junit.Assert.assertEquals;
+
+import com.lmax.disruptor.EventHandler;
+
+public class SingleEventConsumer implements EventConsumer {
+
+    private int expectedValue = -1;
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public EventHandler<ValueEvent>[] getEventHandler() {
+        final EventHandler<ValueEvent> eventHandler = (event, sequence, endOfBatch) -> assertExpectedValue(event.getValue());
+        return new EventHandler[] { eventHandler };
+    }
+
+    private void assertExpectedValue(final int id) {
+        assertEquals(++expectedValue, id);
+    }
+}