Merge pull request #537 from robertt240/master

guarded suspension pattern #69

guarded-suspension/README.md

@@ -0,0 +1,21 @@
+---
+layout: pattern
+title: Guarded Suspension
+folder: guarded-suspension
+permalink: /patterns/guarded-suspension/
+categories: Concurrency
+tags:
+ - Java
+ - Difficulty-Beginner
+---
+
+## Intent
+Use Guarded suspension pattern to handle a situation when you want to execute a method on object which is not in a proper state.
+
+![Guarded Suspension diagram](./etc/guarded-suspension.png)
+
+## Applicability
+Use Guarded Suspension pattern when the developer knows that the method execution will be blocked for a finite period of time
+
+## Related patterns
+* Balking 

guarded-suspension/etc/guarded-suspension.ucls

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.13" icons="true" automaticImage="JPEG" always-add-relationships="false" 
+  generalizations="true" realizations="true" associations="true" dependencies="false" nesting-relationships="true" 
+  router="FAN">  
+  <class id="1" language="java" name="com.iluwatar.guarded.suspension.GuardedQueue" 
+    project="java-design-patterns_guarded-suspension" 
+    file="/java-design-patterns_guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/GuardedQueue.java" 
+    binary="false" corner="BOTTOM_RIGHT">    
+    <position height="277" width="326" x="301" y="172"/>    
+    <display autosize="false" 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>  
+  <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>

guarded-suspension/etc/guarded-suspension.urm.puml

@@ -0,0 +1,11 @@
+@startuml
+package com.iluwatar.guarded.suspension {
+  class GuardedQueue {
+    - LOGGER : Logger {static}
+    - sourceList : Queue<Integer>
+    + GuardedQueue()
+    + get() : Integer
+    + put(e : Integer)
+  }
+}
+@enduml

guarded-suspension/pom.xml

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright (c) 2014 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<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>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.15.0-SNAPSHOT</version>
+  </parent>
+  <packaging>jar</packaging>
+  <artifactId>guarded-suspension</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/App.java

@@ -0,0 +1,76 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+/**
+ * Guarded-suspension is a concurrent design pattern for handling situation when to execute some action we need
+ * condition to be satisfied.
+ * <p>
+ * Implementation is based on GuardedQueue, which has two methods: get and put,
+ * the condition is that we cannot get from empty queue so when thread attempt
+ * to break the condition we invoke Object's wait method on him and when other thread put an element
+ * to the queue he notify the waiting one that now he can get from queue.
+ */
+package com.iluwatar.guarded.suspension;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Created by robertt240 on 1/26/17.
+ */
+public class App {
+  /**
+   * Example pattern execution
+   *
+   * @param args - command line args
+   */
+  public static void main(String[] args) {
+    GuardedQueue guardedQueue = new GuardedQueue();
+    ExecutorService executorService = Executors.newFixedThreadPool(3);
+
+    //here we create first thread which is supposed to get from guardedQueue
+    executorService.execute(() -> {
+          guardedQueue.get();
+        }
+    );
+
+    //here we wait two seconds to show that the thread which is trying to get from guardedQueue will be waiting
+    try {
+      Thread.sleep(2000);
+    } catch (InterruptedException e) {
+      e.printStackTrace();
+    }
+    //now we execute second thread which will put number to guardedQueue and notify first thread that it could get
+    executorService.execute(() -> {
+          guardedQueue.put(20);
+        }
+    );
+    executorService.shutdown();
+    try {
+      executorService.awaitTermination(30, TimeUnit.SECONDS);
+    } catch (InterruptedException e) {
+      e.printStackTrace();
+    }
+  }
+
+}

guarded-suspension/src/main/java/com/iluwatar/guarded/suspension/GuardedQueue.java

@@ -0,0 +1,65 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ * <p>
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.guarded.suspension;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+
+public class GuardedQueue {
+  private static final Logger LOGGER = LoggerFactory.getLogger(GuardedQueue.class);
+  private final Queue<Integer> sourceList;
+
+  public GuardedQueue() {
+    this.sourceList = new LinkedList<>();
+  }
+
+  /**
+   * @return last element of a queue if queue is not empty
+   */
+  public synchronized Integer get() {
+    while (sourceList.isEmpty()) {
+      try {
+        LOGGER.info("waiting");
+        wait();
+      } catch (InterruptedException e) {
+        e.printStackTrace();
+      }
+    }
+    LOGGER.info("getting");
+    return sourceList.peek();
+  }
+
+  /**
+   * @param e number which we want to put to our queue
+   */
+  public synchronized void put(Integer e) {
+    LOGGER.info("putting");
+    sourceList.add(e);
+    LOGGER.info("notifying");
+    notify();
+  }
+}

guarded-suspension/src/test/java/com/iluwatar/guarded/suspension/GuardedQueueTest.java

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+/**
+ * The MIT License
+ * Copyright (c) 2014 Ilkka Seppälä
+ * <p>
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package com.iluwatar.guarded.suspension;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+public class GuardedQueueTest {
+  private volatile Integer value;
+
+  @Test
+  public void testGet() {
+    GuardedQueue g = new GuardedQueue();
+    ExecutorService executorService = Executors.newFixedThreadPool(2);
+    executorService.submit(() -> value = g.get());
+    executorService.submit(() -> g.put(Integer.valueOf(10)));
+    executorService.shutdown();
+    try {
+      executorService.awaitTermination(30, TimeUnit.SECONDS);
+    } catch (InterruptedException e) {
+      e.printStackTrace();
+    }
+    Assert.assertEquals(Integer.valueOf(10), value);
+  }
+
+  @Test
+  public void testPut() {
+    GuardedQueue g = new GuardedQueue();
+    g.put(12);
+    Assert.assertEquals(Integer.valueOf(12), g.get());
+
+  }
+
+}

pom.xml

@@ -121,7 +121,7 @@
         <module>factory-kit</module>
         <module>feature-toggle</module>
         <module>value-object</module>
-		<module>module</module>
+		    <module>module</module>
         <module>monad</module>
         <module>mute-idiom</module>
         <module>mutex</module>
@@ -134,6 +134,8 @@
         <module>event-asynchronous</module>
         <module>queue-load-leveling</module>
         <module>object-mother</module>
+        <module>guarded-suspension</module>
+
     </modules>
 
     <dependencyManagement>