Update according to review comments #397

- Added descriptions
- Added junit tests
- Added javadoc
- Added index.md
- Added class diagrams

mutex/index.md

@@ -0,0 +1,30 @@
+---
+layout: pattern
+title: Mutex
+folder: mutex
+permalink: /patterns/mutex/
+categories: Lock
+tags: 
+ - Java
+ - Difficulty-Beginner
+---
+
+## Also known as
+Mutual Exclusion Lock
+Binary Semaphore
+
+## Intent
+Create a lock which only allows a single thread to access a resource at any one instant.
+
+![alt text](./etc/mutex.png "Mutex")
+
+## Applicability
+Use a Mutex when
+
+* you need to prevent two threads accessing a critical section at the same time
+* concurrent access to a resource could lead to a race condition 
+
+## Credits
+
+* [Lock (computer science)] (http://en.wikipedia.org/wiki/Lock_(computer_science))
+* [Semaphores] (http://tutorials.jenkov.com/java-concurrency/semaphores.html)

mutex/pom.xml

@@ -2,7 +2,7 @@
 <!--
 
     The MIT License
-    Copyright (c) 2014 Ilkka Seppälä
+    Copyright (c) 2014 Ilkka Sepp<EFBFBD>l<EFBFBD>
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -32,4 +32,11 @@
     <version>1.11.0-SNAPSHOT</version>
   </parent>
   <artifactId>mutex</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency> 
+  </dependencies>
 </project>

mutex/src/main/java/com/iluwatar/mutex/App.java

@@ -23,7 +23,15 @@
 package com.iluwatar.mutex;
 
 /**
- * App.
+ * A Mutex prevents multiple threads from accessing a resource simultaneously.
+ * <p>
+ * In this example we have two thieves who are taking beans from a jar.
+ * Only one thief can take a bean at a time. This is ensured by a Mutex lock
+ * which must be acquired in order to access the jar. Each thief attempts to
+ * acquire the lock, take a bean and then release the lock. If the lock has 
+ * already been acquired, the thief will be prevented from continuing (blocked)
+ * until the lock has been released. The thieves stop taking beans once there
+ * are no beans left to take.
  */
 public class App {
 

mutex/src/main/java/com/iluwatar/mutex/Jar.java

@@ -23,12 +23,20 @@
 package com.iluwatar.mutex;
 
 /**
- * Jar.
+ * A Jar has a resource of beans which can only be accessed by a single Thief
+ * (thread) at any one time. A Mutex lock is used to prevent more than one Thief
+ * taking a bean simultaneously. 
  */
 public class Jar {
 
-  private Lock lock;
+  /**
+   * The lock which must be acquired to access the beans resource.
+   */
+  private final Lock lock;
 
+  /**
+   * The resource within the jar.
+   */
   private int beans = 1000;
 
   public Jar(Lock lock) {
@@ -36,7 +44,7 @@ public class Jar {
   }
 
   /**
-   * takeBean method
+   * Method for a thief to take a bean.
    */
   public boolean takeBean(Thief thief) {
     boolean success = false;

mutex/src/main/java/com/iluwatar/mutex/Lock.java

@@ -23,7 +23,7 @@
 package com.iluwatar.mutex;
 
 /**
- * Lock.
+ * Lock is an interface for a lock which can be acquired and released.
  */
 public interface Lock {
 

mutex/src/main/java/com/iluwatar/mutex/Mutex.java

@@ -23,11 +23,20 @@
 package com.iluwatar.mutex;
 
 /**
- * Mutex.
+ * Mutex is an implementation of a mutual exclusion lock.
  */
 public class Mutex implements Lock {
-  private Object owner = null;
 
+  /**
+   * The current owner of the lock.
+   */
+  private Object owner;
+
+  /**
+   * Method called by a thread to acquire the lock. If the lock has already
+   * been acquired this will wait until the lock has been released to 
+   * re-attempt the acquire.
+   */
   @Override
   public synchronized void acquire() throws InterruptedException {
     while (owner != null) {
@@ -37,6 +46,9 @@ public class Mutex implements Lock {
     owner = Thread.currentThread();
   }
 
+  /**
+   * Method called by a thread to release the lock.
+   */
   @Override
   public synchronized void release() {
     owner = null;

mutex/src/main/java/com/iluwatar/mutex/Thief.java

@@ -23,19 +23,30 @@
 package com.iluwatar.mutex;
 
 /**
- * Thief.
+ * Thief is a class which continually tries to acquire a jar and take a bean
+ * from it. When the jar is empty the thief stops.
  */
 public class Thief extends Thread {
 
-  private String name;
+  /**
+   * The name of the thief. 
+   */
+  private final String name;
   
-  private Jar jar;
+  /**
+   * The jar
+   */
+  private final Jar jar;
 
   public Thief(String name, Jar jar) {
     this.name = name;
     this.jar = jar;
   }
 
+  /**
+   * In the run method the thief repeatedly tries to take a bean until none
+   * are left.
+   */
   @Override
   public void run() {
     int beans = 0;

mutex/src/test/java/com/iluwatar/mutex/AppTest.java

@@ -0,0 +1,34 @@
+/**
+ * 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.
+ */
+package com.iluwatar.mutex;
+
+import org.junit.Test;
+import java.io.IOException;
+
+public class AppTest{
+  @Test
+  public void test() throws IOException {
+    String[] args = {};
+    App.main(args);
+  }
+}

semaphore/index.md

@@ -0,0 +1,33 @@
+---
+layout: pattern
+title: Semaphore
+folder: semaphore
+permalink: /patterns/semaphore/
+categories: Lock
+tags: 
+ - Java
+ - Difficulty-Beginner
+---
+
+## Also known as
+Counting Semaphore
+
+## Intent
+Create a lock which mediates access to a pool of resources. 
+Only a limited number of threads, specified at the creation 
+of the semaphore, can access the resources at any given time.
+A semaphore which only allows one concurrent access to a resource
+is called a binary semaphore.
+
+![alt text](./etc/semaphore.png "Semaphore")
+
+## Applicability
+Use a Semaphore when 
+
+* you have a pool of resources to allocate to different threads
+* concurrent access to a resource could lead to a race condition 
+
+## Credits
+
+* [Semaphore(programming)] (http://en.wikipedia.org/wiki/Semaphore_(programming))
+* [Semaphores] (http://tutorials.jenkov.com/java-concurrency/semaphores.html)

semaphore/pom.xml

@@ -2,7 +2,7 @@
 <!--
 
     The MIT License
-    Copyright (c) 2014 Ilkka Seppälä
+    Copyright (c) 2014 Ilkka Sepp<EFBFBD>l<EFBFBD>
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -32,4 +32,11 @@
     <version>1.11.0-SNAPSHOT</version>
   </parent>
   <artifactId>semaphore</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
 </project>

semaphore/src/main/java/com/iluwatar/semaphore/App.java

@@ -23,7 +23,14 @@
 package com.iluwatar.semaphore;
 
 /**
- * App.
+ * A Semaphore mediates access by a group of threads to a pool of resources.
+ * <p>
+ * In this example a group of customers are taking fruit from a fruit shop.
+ * There is a bowl each of apples, oranges and lemons. Only one customer can 
+ * access a bowl simultaneously. A Semaphore is used to indicate how many 
+ * resources are currently available and must be acquired in order for a bowl 
+ * to be given to a customer. Customers continually try to take fruit until 
+ * there is no fruit left in the shop. 
  */
 public class App {
     

semaphore/src/main/java/com/iluwatar/semaphore/Customer.java

@@ -23,13 +23,25 @@
 package com.iluwatar.semaphore;
 
 /**
- * Customer.
+ * A Customer attempts to repeatedly take Fruit from the FruitShop by
+ * taking Fruit from FruitBowl instances.
  */
 public class Customer extends Thread {
 
-  private String name;
+  /**
-  private FruitShop fruitShop;
+   * Name of the Customer.
-  private FruitBowl fruitBowl;
+   */
+  private final String name;
+  
+  /**
+   * The FruitShop he is using.
+   */
+  private final FruitShop fruitShop;
+  
+  /**
+   * Their bowl of Fruit.
+   */
+  private final FruitBowl fruitBowl;
   
   /**
    * Customer constructor
@@ -41,7 +53,8 @@ public class Customer extends Thread {
   }
   
   /**
-   * run method
+   * The Customer repeatedly takes Fruit from the FruitShop until no Fruit
+   * remains.
    */   
   public void run() {
         

semaphore/src/main/java/com/iluwatar/semaphore/Fruit.java

@@ -23,7 +23,7 @@
 package com.iluwatar.semaphore;
 
 /**
- * Fruit.
+ * Fruit is a resource stored in a FruitBowl. 
  */
 public class Fruit {
 

semaphore/src/main/java/com/iluwatar/semaphore/FruitBowl.java

@@ -25,22 +25,32 @@ package com.iluwatar.semaphore;
 import java.util.ArrayList;
 
 /**
- * FruitBowl.
+ * A FruitBowl contains Fruit. 
  */
 public class FruitBowl {
     
   private ArrayList<Fruit> fruit = new ArrayList<>();
 
+  /**
+   * 
+   * @return The amount of Fruit left in the bowl. 
+   */
   public int countFruit() {
     return fruit.size();
   }
 
+  /**
+   * Put an item of Fruit into the bowl.
+   * 
+   * @param f fruit
+   */
   public void put(Fruit f) {
     fruit.add(f);
   }
   
   /**
-   * take method
+   * Take an item of Fruit out of the bowl.
+   * @return The Fruit taken out of the bowl, or null if empty.
    */
   public Fruit take() {
     if (fruit.isEmpty()) {

semaphore/src/main/java/com/iluwatar/semaphore/FruitShop.java

@@ -23,22 +23,31 @@
 package com.iluwatar.semaphore;
 
 /**
- * FruitShop.
+ * A FruitShop contains three FruitBowl instances and controls access to them.
  */
 public class FruitShop {
    
+  /**
+   * The FruitBowl instances stored in the class.
+   */
   private FruitBowl[] bowls = {
     new FruitBowl(),
     new FruitBowl(),
     new FruitBowl()
   };
 
+  /**
+   * Access flags for each of the FruitBowl instances.
+   */
   private boolean[] available = {
     true,
     true,
     true
   };
 
+  /**
+   * The Semaphore that controls access to the class resources.
+   */
   private Semaphore semaphore;
   
   /**
@@ -54,12 +63,18 @@ public class FruitShop {
     semaphore = new Semaphore(3);
   }
 
+  /**
+   * 
+   * @return The amount of Fruit left in the shop.
+   */
   public synchronized int countFruit() {
     return bowls[0].countFruit() + bowls[1].countFruit() + bowls[2].countFruit();
   }
   
   /**
-   * takeBowl method
+   * Method called by Customer to get a FruitBowl from the shop. This method
+   * will try to acquire the Semaphore before returning the first available 
+   * FruitBowl.
    */   
   public synchronized FruitBowl takeBowl() {
         
@@ -88,7 +103,9 @@ public class FruitShop {
   }
   
   /**
-   * returnBowl method
+   * Method called by a Customer instance to return a FruitBowl to the shop. 
+   * This method releases the Semaphore, making the FruitBowl available to 
+   * another Customer.
    */   
   public synchronized void returnBowl(FruitBowl bowl) {
     if (bowl == bowls[0]) {

semaphore/src/main/java/com/iluwatar/semaphore/Lock.java

@@ -23,7 +23,7 @@
 package com.iluwatar.semaphore;
 
 /**
- * Lock.
+ * Lock is an interface for a lock which can be acquired and released.
  */
 public interface Lock {
     

semaphore/src/main/java/com/iluwatar/semaphore/Semaphore.java

@@ -23,10 +23,13 @@
 package com.iluwatar.semaphore;
 
 /**
- * Semaphore.
+ * Semaphore is an implementation of a semaphore lock.
  */
 public class Semaphore implements Lock {
 
+  /**
+   * The number of concurrent resource accesses which are allowed.
+   */
   private int counter;
     
   public Semaphore(int counter) {
@@ -34,7 +37,9 @@ public class Semaphore implements Lock {
   }
   
   /**
-   * acquire method
+   * Method called by a thread to acquire the lock. If there are no resources
+   * available this will wait until the lock has been released to re-attempt
+   * the acquire.
    */
   public synchronized void acquire() throws InterruptedException {
     while (counter == 0) {
@@ -43,6 +48,9 @@ public class Semaphore implements Lock {
     counter = counter - 1;
   }
   
+  /**
+   * Method called by a thread to release the lock.
+   */
   public synchronized void release() {
     counter = counter + 1;
     notify();

semaphore/src/test/java/com/iluwatar/semaphore/AppTest.java

@@ -0,0 +1,34 @@
+/**
+ * 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.
+ */
+package com.iluwatar.semaphore;
+
+import org.junit.Test;
+import java.io.IOException;
+
+public class AppTest{
+  @Test
+  public void test() throws IOException {
+    String[] args = {};
+    App.main(args);
+  }
+}