From dc0f578f8b06c22ea33dfbf2be46e38036d2d006 Mon Sep 17 00:00:00 2001
From: vehpsr <vehpsrr@gmail.com>
Date: Sun, 5 Apr 2015 18:03:16 +0300
Subject: [PATCH] added Poison Pill idiom

---
 README.md                                     |   9 +-
 poison-pill/etc/poison-pill.png               | Bin 0 -> 15833 bytes
 poison-pill/etc/poison-pill.ucls              |  92 ++++++++++++++++++
 poison-pill/pom.xml                           |  18 ++++
 .../src/main/java/com/iluwatar/App.java       |  37 +++++++
 .../src/main/java/com/iluwatar/Consumer.java  |  38 ++++++++
 .../java/com/iluwatar/MQPublishPoint.java     |   9 ++
 .../java/com/iluwatar/MQSubscribePoint.java   |   9 ++
 .../src/main/java/com/iluwatar/Message.java   |  52 ++++++++++
 .../main/java/com/iluwatar/MessageQueue.java  |   8 ++
 .../src/main/java/com/iluwatar/Producer.java  |  48 +++++++++
 .../main/java/com/iluwatar/SimpleMessage.java |  39 ++++++++
 .../java/com/iluwatar/SimpleMessageQueue.java |  27 +++++
 .../src/test/java/com/iluwatar/AppTest.java   |  12 +++
 pom.xml                                       |   1 +
 15 files changed, 398 insertions(+), 1 deletion(-)
 create mode 100644 poison-pill/etc/poison-pill.png
 create mode 100644 poison-pill/etc/poison-pill.ucls
 create mode 100644 poison-pill/pom.xml
 create mode 100644 poison-pill/src/main/java/com/iluwatar/App.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/Consumer.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/MQPublishPoint.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/MQSubscribePoint.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/Message.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/MessageQueue.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/Producer.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/SimpleMessage.java
 create mode 100644 poison-pill/src/main/java/com/iluwatar/SimpleMessageQueue.java
 create mode 100644 poison-pill/src/test/java/com/iluwatar/AppTest.java

diff --git a/README.md b/README.md
index f584edc61..90d487b91 100644
--- a/README.md
+++ b/README.md
@@ -71,7 +71,7 @@ A programming idiom is a means of expressing a recurring construct in one or mor
 
 * [Execute Around](#execute-around)
 * [Double Checked Locking](#double-checked-locking)
-
+* [Poison Pill](#poison-pill)
 
 
 ## <a name="abstract-factory">Abstract Factory</a> [&#8593;](#list-of-design-patterns)
@@ -475,6 +475,13 @@ A programming idiom is a means of expressing a recurring construct in one or mor
 **Real world examples:**
 * [JavaScript](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain) prototype inheritance
 
+## <a name="poison-pill">Poison Pill</a> [&#8593;](#list-of-design-patterns)
+**Intent:** Poison Pill is known predefined data item that allows to provide graceful shutdown for separate distributed consumption process.
+
+![alt text](https://github.com/iluwatar/java-design-patterns/blob/master/poison-pill/etc/poison-pill.png "Poison Pill")
+
+**Applicability:** Use the Poison Pill idiom when
+* need to send signal from one thread/process to another to terminate
 
 # Frequently asked questions
 
diff --git a/poison-pill/etc/poison-pill.png b/poison-pill/etc/poison-pill.png
new file mode 100644
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Szj%*bpdhCzTP*YR)&B>iXFe1F

literal 0
HcmV?d00001

diff --git a/poison-pill/etc/poison-pill.ucls b/poison-pill/etc/poison-pill.ucls
new file mode 100644
index 000000000..6d20b1974
--- /dev/null
+++ b/poison-pill/etc/poison-pill.ucls
@@ -0,0 +1,92 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
+  <class id="1" language="java" name="com.iluwatar.Producer" project="poison-pill" 
+    file="/poison-pill/src/main/java/com/iluwatar/Producer.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="153" width="182" x="158" y="209"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <interface id="2" language="java" name="com.iluwatar.MQPublishPoint" project="poison-pill" 
+    file="/poison-pill/src/main/java/com/iluwatar/MQPublishPoint.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="453" y="283"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <class id="3" language="java" name="com.iluwatar.SimpleMessageQueue" project="poison-pill" 
+    file="/poison-pill/src/main/java/com/iluwatar/SimpleMessageQueue.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="627" y="115"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <interface id="4" language="java" name="com.iluwatar.MessageQueue" project="poison-pill" 
+    file="/poison-pill/src/main/java/com/iluwatar/MessageQueue.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="627" y="283"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <interface id="5" language="java" name="com.iluwatar.MQSubscribePoint" project="poison-pill" 
+    file="/poison-pill/src/main/java/com/iluwatar/MQSubscribePoint.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="821" y="282"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <class id="6" language="java" name="com.iluwatar.Consumer" project="poison-pill" 
+    file="/poison-pill/src/main/java/com/iluwatar/Consumer.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1055" y="282"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <generalization id="7">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="2"/>  
+  </generalization>  
+  <realization id="8">    
+    <end type="SOURCE" refId="3"/>    
+    <end type="TARGET" refId="4"/>  
+  </realization>  
+  <generalization id="9">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="5"/>  
+  </generalization>  
+  <association id="10">    
+    <end type="SOURCE" refId="6" navigable="false">      
+      <attribute id="11" name="queue"/>      
+      <multiplicity id="12" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="5" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="13">    
+    <end type="SOURCE" refId="1" navigable="false">      
+      <attribute id="14" name="queue"/>      
+      <multiplicity id="15" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="2" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>
\ No newline at end of file
diff --git a/poison-pill/pom.xml b/poison-pill/pom.xml
new file mode 100644
index 000000000..1d9d4c38a
--- /dev/null
+++ b/poison-pill/pom.xml
@@ -0,0 +1,18 @@
+<?xml version="1.0"?>
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>poison-pill</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>
diff --git a/poison-pill/src/main/java/com/iluwatar/App.java b/poison-pill/src/main/java/com/iluwatar/App.java
new file mode 100644
index 000000000..22de1dd28
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/App.java
@@ -0,0 +1,37 @@
+package com.iluwatar;
+
+/**
+ * One of possible approaches to terminate Producer-Consumer pattern is using PoisonPill idiom.
+ * If you use PoisonPill as termination signal then Producer is responsible to notify Consumer that exchange is over
+ * and reject any further messages. Consumer receiving PoisonPill will stop to read messages from queue.
+ * You also must ensure that PoisonPill will be last message that will be read from queue (if you have
+ * prioritized queue than this can be tricky).
+ * In simple cases as PoisonPill can be used just null-reference, but holding unique separate shared
+ * object-marker (with name "Poison" or "PoisonPill") is more clear and self describing.
+ */
+public class App {
+
+	public static void main(String[] args) {
+		MessageQueue queue = new SimpleMessageQueue(10000);
+
+		final Producer producer = new Producer("PRODUCER_1", queue);
+		final Consumer consumer = new Consumer("CONSUMER_1", queue);
+
+		new Thread() {
+			@Override
+			public void run() {
+				consumer.consume();
+			}
+		}.start();
+
+		new Thread() {
+			@Override
+			public void run() {
+				producer.send("hand shake");
+				producer.send("some very important information");
+				producer.send("bye!");
+				producer.stop();
+			}
+		}.start();
+	}
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/Consumer.java b/poison-pill/src/main/java/com/iluwatar/Consumer.java
new file mode 100644
index 000000000..499971b6c
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/Consumer.java
@@ -0,0 +1,38 @@
+package com.iluwatar;
+
+import com.iluwatar.Message.Headers;
+
+/**
+ * Class responsible for receiving and handling submitted to the queue messages
+ */
+public class Consumer {
+
+	private final MQSubscribePoint queue;
+	private final String name;
+
+	public Consumer(String name, MQSubscribePoint queue) {
+		this.name = name;
+		this.queue = queue;
+	}
+
+	public void consume() {
+		while (true) {
+			Message msg;
+			try {
+				msg = queue.take();
+				if (msg == Message.POISON_PILL) {
+					System.out.println(String.format("Consumer %s receive request to terminate.", name));
+					break;
+				}
+			} catch (InterruptedException e) {
+				// allow thread to exit
+				System.err.println(e);
+				return;
+			}
+
+			String sender = msg.getHeader(Headers.SENDER);
+			String body = msg.getBody();
+			System.out.println(String.format("Message [%s] from [%s] received by [%s]", body, sender, name));
+		}
+	}
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/MQPublishPoint.java b/poison-pill/src/main/java/com/iluwatar/MQPublishPoint.java
new file mode 100644
index 000000000..6cc830e71
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/MQPublishPoint.java
@@ -0,0 +1,9 @@
+package com.iluwatar;
+
+/**
+ * Endpoint to publish {@link Message} to queue
+ */
+public interface MQPublishPoint {
+
+	public void put(Message msg) throws InterruptedException;
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/MQSubscribePoint.java b/poison-pill/src/main/java/com/iluwatar/MQSubscribePoint.java
new file mode 100644
index 000000000..5e15ba7b9
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/MQSubscribePoint.java
@@ -0,0 +1,9 @@
+package com.iluwatar;
+
+/**
+ * Endpoint to retrieve {@link Message} from queue
+ */
+public interface MQSubscribePoint {
+
+	public Message take() throws InterruptedException;
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/Message.java b/poison-pill/src/main/java/com/iluwatar/Message.java
new file mode 100644
index 000000000..e9a67fe59
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/Message.java
@@ -0,0 +1,52 @@
+package com.iluwatar;
+
+import java.util.Map;
+
+/**
+ * Interface that implements the Message pattern and represents an inbound or outbound message as part of an {@link Producer}-{@link Consumer} exchange.
+ */
+public interface Message {
+
+	public static final Message POISON_PILL = new Message() {
+
+		@Override
+		public void addHeader(Headers header, String value) {
+			throw poison();
+		}
+
+		@Override
+		public String getHeader(Headers header) {
+			throw poison();
+		}
+
+		@Override
+		public Map<Headers, String> getHeaders() {
+			throw poison();
+		}
+
+		@Override
+		public void setBody(String body) {
+			throw poison();
+		}
+
+		@Override
+		public String getBody() {
+			throw poison();
+		}
+
+		private RuntimeException poison() {
+			return new UnsupportedOperationException("Poison");
+		}
+
+	};
+
+	public enum Headers {
+		DATE, SENDER
+	}
+
+	public void addHeader(Headers header, String value);
+	public String getHeader(Headers header);
+	public Map<Headers, String> getHeaders();
+	public void setBody(String body);
+	public String getBody();
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/MessageQueue.java b/poison-pill/src/main/java/com/iluwatar/MessageQueue.java
new file mode 100644
index 000000000..03ced489b
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/MessageQueue.java
@@ -0,0 +1,8 @@
+package com.iluwatar;
+
+/**
+ * Represents abstraction of channel (or pipe) that bounds {@link Producer} and {@link Consumer}
+ */
+public interface MessageQueue extends MQPublishPoint, MQSubscribePoint {
+
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/Producer.java b/poison-pill/src/main/java/com/iluwatar/Producer.java
new file mode 100644
index 000000000..89fb75277
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/Producer.java
@@ -0,0 +1,48 @@
+package com.iluwatar;
+
+import java.util.Date;
+
+import com.iluwatar.Message.Headers;
+
+/**
+ * Class responsible for producing unit of work that can be expressed as message and submitted to queue
+ */
+public class Producer {
+
+	private final MQPublishPoint queue;
+	private final String name;
+	private boolean isStopped;
+
+	public Producer(String name, MQPublishPoint queue) {
+		this.name = name;
+		this.queue = queue;
+		this.isStopped = false;
+	}
+
+	public void send(String body) {
+		if (isStopped) {
+			throw new IllegalStateException(String.format("Producer %s was stopped and fail to deliver requested message [%s].", body, name));
+		}
+		Message msg = new SimpleMessage();
+		msg.addHeader(Headers.DATE, new Date().toString());
+		msg.addHeader(Headers.SENDER, name);
+		msg.setBody(body);
+
+		try {
+			queue.put(msg);
+		} catch (InterruptedException e) {
+			// allow thread to exit
+			System.err.println(e);
+		}
+	}
+
+	public void stop() {
+		isStopped = true;
+		try {
+			queue.put(Message.POISON_PILL);
+		} catch (InterruptedException e) {
+			// allow thread to exit
+			System.err.println(e);
+		}
+	}
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/SimpleMessage.java b/poison-pill/src/main/java/com/iluwatar/SimpleMessage.java
new file mode 100644
index 000000000..27b8db08b
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/SimpleMessage.java
@@ -0,0 +1,39 @@
+package com.iluwatar;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * {@link Message} basic implementation
+ */
+public class SimpleMessage implements Message {
+
+	private Map<Headers, String> headers = new HashMap<>();
+	private String body;
+
+	@Override
+	public void addHeader(Headers header, String value) {
+		headers.put(header, value);
+	}
+
+	@Override
+	public String getHeader(Headers header) {
+		return headers.get(header);
+	}
+
+	@Override
+	public Map<Headers, String> getHeaders() {
+		return Collections.unmodifiableMap(headers);
+	}
+
+	@Override
+	public void setBody(String body) {
+		this.body = body;
+	}
+
+	@Override
+	public String getBody() {
+		return body;
+	}
+}
diff --git a/poison-pill/src/main/java/com/iluwatar/SimpleMessageQueue.java b/poison-pill/src/main/java/com/iluwatar/SimpleMessageQueue.java
new file mode 100644
index 000000000..12d519ce2
--- /dev/null
+++ b/poison-pill/src/main/java/com/iluwatar/SimpleMessageQueue.java
@@ -0,0 +1,27 @@
+package com.iluwatar;
+
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.BlockingQueue;
+
+/**
+ * Bounded blocking queue wrapper
+ */
+public class SimpleMessageQueue implements MessageQueue {
+
+	private final BlockingQueue<Message> queue;
+
+	public SimpleMessageQueue(int bound) {
+		queue = new ArrayBlockingQueue<Message>(bound);
+	}
+
+	@Override
+	public void put(Message msg) throws InterruptedException {
+		queue.put(msg);
+	}
+
+	@Override
+	public Message take() throws InterruptedException {
+		return queue.take();
+	}
+
+}
diff --git a/poison-pill/src/test/java/com/iluwatar/AppTest.java b/poison-pill/src/test/java/com/iluwatar/AppTest.java
new file mode 100644
index 000000000..6db5ad214
--- /dev/null
+++ b/poison-pill/src/test/java/com/iluwatar/AppTest.java
@@ -0,0 +1,12 @@
+package com.iluwatar;
+
+import org.junit.Test;
+
+public class AppTest {
+
+	@Test
+	public void test() {
+		String[] args = {};
+		App.main(args);
+	}
+}
diff --git a/pom.xml b/pom.xml
index d81be42c9..d05182607 100644
--- a/pom.xml
+++ b/pom.xml
@@ -44,6 +44,7 @@
 		<module>execute-around</module>
 		<module>property</module>
 		<module>intercepting-filter</module>
+		<module>poison-pill</module>
 	</modules>
 
 	<dependencyManagement>