Zookeeper 官方示例2-SyncPrimitive 代码解读（二）

测试命令
java jar .\ZookeeperDemo-0.0.1-SNAPSHOT.jar bTest 192.168.206.100:2181 2

1. Barrier（阻塞原语）

1.1 概念

[!quote] A barrier is a primitive that enables a group of processes to synchronize the beginning and the end of a computation. The general idea of this implementation is to have a barrier node that serves the purpose of being a parent for individual process nodes. Suppose that we call the barrier node "/b1". Each process "p" then creates a node "/b1/p". Once enough processes have created their corresponding nodes, joined processes can start the computation.

阻塞是一个原语，它使一组进程能够同时开始计算。此实现的总体思想是拥有一个屏障节点，用于作为单个流程节点的父节点。
假设我们将障碍节点称为“/b1”。然后，每个进程“ p”创建一个节点“/b1/p”。一旦有足够多的进程创建了相应的节点，联合进程就可以开始计算了。
场景：当有些操作需要所有参与者全部准备好之后才能开始执行，并且对每个参与者来说必须等待所有参与者全部执行完毕，才算执行完毕。于是就需要一个屏障，来控制所有参与者同时开始，并等待所有参与者全部结束。

1.2 设计

创建一个/b1的znode的持久化节点。
enter() 模拟往阻塞里增加执行进程（Join barrier）。往znode下增加子节点，并判断子节点数是否满足指定的个数n。若未满足条件则继续等待；反之则返回true。
leave() 模拟进程执行完毕后的离开（Wait until all reach barrier）。删除znode的子节点，并判断子节点是否大于0，若大于0则表示还有子进程没有执行完。

源码:

package com.agileluo.zookeeperdemo.barriers;  
import java.io.IOException;  
import java.net.InetAddress;  
import java.net.UnknownHostException;  
import java.nio.ByteBuffer;  
import java.util.List;  
import java.util.Random;  
import java.lang.Integer;  
import org.apache.commons.lang3.RandomStringUtils;  
import org.apache.zookeeper.CreateMode;  
import org.apache.zookeeper.KeeperException;  
import org.apache.zookeeper.WatchedEvent;  
import org.apache.zookeeper.Watcher;  
import org.apache.zookeeper.ZooKeeper;  
import org.apache.zookeeper.ZooDefs.Ids;  
import org.apache.zookeeper.data.Stat;  /**  * 1. Queue test * 1.1 Start a producer to create 100 elements *    java SyncPrimitive qTest localhost 100 p * 1.2 Start a consumer to consume 100 elements *    java SyncPrimitive qTest localhost 100 c * * 2.Barrier test * Start a barrier with 2 participants (start as many times as many participants you'd like to enter) *    java SyncPrimitive bTest localhost 2 */public class SyncPrimitive implements Watcher {  static ZooKeeper zk = null;  static Integer mutex;  String root;  static{  System.setProperty("zookeeper.sasl.client", "false");  }  SyncPrimitive(String address) {  if(zk == null){  try {  System.out.println("Starting ZK:");  zk = new ZooKeeper(address, 3000, this);  mutex = Integer.parseInt("-1");  System.out.println("Finished starting ZK: " + zk);  } catch (IOException e) {  System.out.println(e.toString());  zk = null;  }  }  //else mutex = new Integer(-1);  }  synchronized public void process(WatchedEvent event) {  synchronized (mutex) {  //System.out.println("Process: " + event.getType());  mutex.notify();  }  }  /**  * Barrier（阻塞原语）  *  A barrier is a primitive that enables a group of processes to synchronize the beginning and the end of a computation. The general idea of this implementation is to  *  have a barrier node that serves the purpose of being a parent for individual process nodes. Suppose that we call the barrier node &quot;/b1&quot;. Each process  *  &quot;p&quot; then creates a node &quot;/b1/p&quot;. Once enough processes have created their corresponding nodes, joined processes can start the computation.  *  阻塞是一个原语，它使一组进程能够同时开始计算。此实现的总体思想是拥有一个屏障节点，用于作为单个流程节点的父节点。  *  假设我们将障碍节点称为“/b1”。然后，每个进程“ p”创建一个节点“/b1/p”。一旦有足够多的进程创建了相应的节点，联合进程就可以开始计算了。  *  场景：当有些操作需要所有参与者全部准备好之后才能开始执行，并且对每个参与者来说必须等待所有参与者全部执行完毕，才算执行完毕。于是就需要一个屏障，来控制所有参与者同时开始，并等待所有参与者全部结束。  */  static public class Barrier extends SyncPrimitive {  //需要并行等待的子进程个数  int size;  /**  *  本参与者对应的子节点path  */        String name;  /**  * Barrier constructor         *         * @param address  * @param root  * @param size  */  Barrier(String address, String root, int size) {  super(address);  this.root = root;  this.size = size;  // Create barrier node（障碍节点必须是持久节点 CreateMode.PERSISTENT）  if (zk != null) {  try {  Stat s = zk.exists(root, false);  if (s == null) { // 如果根节点不存在，则创建  /**  *  zk.create(String path, byte[] data, List<ACL> acl, CreateMode createMode)                         *  第1个参数： barrier节点的path  *  第2个参数： barrier节点的data  *  第3个参数： barrier节点的权限  *  第4个参数： barrier 节点的类型，持久节点 CreateMode.PERSISTENT，子节点必须是临时节点。  */  zk.create(root, new byte[0], Ids.OPEN_ACL_UNSAFE,  CreateMode.PERSISTENT);  }  } catch (KeeperException e) {  System.out  .println("Keeper exception when instantiating queue: "  + e.toString());  } catch (InterruptedException e) {  System.out.println("Interrupted exception");  }  }  // My node name  try {  name = new String(InetAddress.getLocalHost().getCanonicalHostName().toString()+ ":"+ RandomStringUtils.randomAlphabetic(4));  } catch (UnknownHostException e) {  System.out.println(e.toString());  }  }  /**  * Join barrier         *         * @return         * @throws KeeperException  * @throws InterruptedException  */  boolean enter() throws KeeperException, InterruptedException{  zk.create(root + "/" + name, new byte[0], Ids.OPEN_ACL_UNSAFE,  CreateMode.EPHEMERAL); // EPHEMERAL 临时节点  while (true) {  synchronized (mutex) {  List<String> list = zk.getChildren(root, true);  if (list.size() < size) { //判断当前根下子节点的数量，若数量小于设定的进程数，则等待。  mutex.wait();  } else {  return true;  }  }  }  }  /**  * Wait until all reach barrier         *         * @return         * @throws KeeperException  * @throws InterruptedException  */  boolean leave() throws KeeperException, InterruptedException{  zk.delete(root + "/" + name, 0); //模拟进程完成任务，删除子节点。  while (true) {  synchronized (mutex) {  List<String> list = zk.getChildren(root, true);  if (list.size() > 0) { //只要还存在子节点，就说明还有任务没有完成。  mutex.wait();  } else {  return true;  }  }  }  }  }  /**  * Producer-Consumer queue     */    static public class Queue extends SyncPrimitive {  /**  * Constructor of producer-consumer queue         *         * @param address  * @param name  */  Queue(String address, String name) {  super(address);  this.root = name;  // Create ZK node name  if (zk != null) {  try {  Stat s = zk.exists(root, false);  if (s == null) {  zk.create(root, new byte[0], Ids.OPEN_ACL_UNSAFE,  CreateMode.PERSISTENT);  }  } catch (KeeperException e) {  System.out  .println("Keeper exception when instantiating queue: "  + e.toString());  } catch (InterruptedException e) {  System.out.println("Interrupted exception");  }  }  }  /**  * Add element to the queue.         *         * @param i  * @return  */  boolean produce(int i) throws KeeperException, InterruptedException{  ByteBuffer b = ByteBuffer.allocate(4);  byte[] value;  // Add child with value i  b.putInt(i);  value = b.array();  zk.create(root + "/element", value, Ids.OPEN_ACL_UNSAFE,  CreateMode.PERSISTENT_SEQUENTIAL);  return true;  }  /**  * Remove first element from the queue.         *         * @return         * @throws KeeperException  * @throws InterruptedException  */  int consume() throws KeeperException, InterruptedException{  int retvalue = -1;  Stat stat = null;  // Get the first element available  while (true) {  synchronized (mutex) {  List<String> list = zk.getChildren(root, true);  if (list.size() == 0) {  System.out.println("Going to wait");  mutex.wait();  } else {  Integer min = Integer.parseInt((list.get(0).substring(7)));  String minNode = list.get(0);  for(String s : list){  Integer tempValue = Integer.parseInt(s.substring(7));  //System.out.println("Temporary value: " + tempValue);  if(tempValue < min) {  min = tempValue;  minNode = s;  }  }  System.out.println("Temporary value: " + root + "/" + minNode);  byte[] b = zk.getData(root + "/" + minNode,  false, stat);  zk.delete(root + "/" + minNode, 0);  ByteBuffer buffer = ByteBuffer.wrap(b);  retvalue = buffer.getInt();  return retvalue;  }  }  }  }  }  public static void main(String args[]) {  if (args[0].equals("qTest"))  queueTest(args);  else  barrierTest(args);  }  public static void queueTest(String args[]) {  Queue q = new Queue(args[1], "/app1");  System.out.println("Input: " + args[1]);  int i;  Integer max = Integer.parseInt(args[2]+"");  if (args[3].equals("p")) {  System.out.println("Producer");  for (i = 0; i < max; i++)  try{  q.produce(10 + i);  } catch (KeeperException e){  } catch (InterruptedException e){  }  } else {  System.out.println("Consumer");  for (i = 0; i < max; i++) {  try{  int r = q.consume();  System.out.println("Item: " + r);  } catch (KeeperException e){  i--;  } catch (InterruptedException e){  }  }  }  }  public static void barrierTest(String args[]) {  Barrier b = new Barrier(args[1], "/b1", Integer.parseInt(args[2]+""));  try{  boolean flag = b.enter();  System.out.println("Entered barrier: " + args[2]);  if(!flag) System.out.println("Error when entering the barrier");  } catch (KeeperException e){  } catch (InterruptedException e){  }  // Generate random integer  Random rand = new Random();  int r = rand.nextInt(100);  // Loop for rand iterations  for (int i = 0; i < r; i++) {  try {  Thread.sleep(100);  } catch (InterruptedException e) {  }  }  try{  b.leave();  } catch (KeeperException e){  } catch (InterruptedException e){  }  System.out.println("Left barrier");  }  
}

1.3 测试步骤

第1步，打包 ZookeeperDemo-0.0.1-SNAPSHOT.jar

<build>  <plugins>  <plugin>  <groupId>org.apache.maven.plugins</groupId>  <artifactId>maven-jar-plugin</artifactId>  <configuration>  <archive>  <manifest>  <addClasspath>true</addClasspath>  <mainClass>com.xx.zookeeperdemo.barriers.SyncPrimitive</mainClass> </manifest>  </archive>  </configuration>  </plugin>  </plugins>  
</build>

第2步，jar包目录下打开命令窗口，并执行 java -jar .\ZookeeperDemo-0.0.1-SNAPSHOT.jar bTest 192.168.206.100:2181 3
控制台输出：

执行后，查看zookeeper的znode情况:

第3步，复制第2步操作，模拟启动第2个进程
执行后，查看zookeeper的znode情况：
第4步，复制第2步操作，模拟启动第3个进程
执行后，第1个控制台输出：

第2个控制台输出：

第3个控制台输出：

然后所有进程在随机的整数时间后输出 Left barrier

查看zookeeper的znode情况：所有子进程创建的临时子节点都已delete

1.4 结果

能实现多个进程之间的并行协同。

1.5 注意事项

为了方便在同一台IP上模拟不同的进程，在官方提供的代码基础上增加了4位长度的随机字符串。


// 官方示例：
name = new String(InetAddress.getLocalHost().getCanonicalHostName().toString());// 新增后的示例
name = new String(InetAddress.getLocalHost().getCanonicalHostName().toString()+ ":"+ RandomStringUtils.randomAlphabetic(4));

关闭SASL安全验证

static{  System.setProperty("zookeeper.sasl.client", "false");  
}

2. 队列

2.1 概念

模拟向同一队列生产/消费消息。

2.2 设计

生产消息：往znode新增子节点。
消费消息：往znode中取first子节点，然后删除子节点。

2.3 源码

/**  * Producer-Consumer queue */static public class Queue extends SyncPrimitive {  /**  * Constructor of producer-consumer queue     *     * @param address  * @param name  */  Queue(String address, String name) {  super(address);  this.root = name;  // Create ZK node name  if (zk != null) {  try {  Stat s = zk.exists(root, false);  if (s == null) {  zk.create(root, new byte[0], Ids.OPEN_ACL_UNSAFE,  CreateMode.PERSISTENT);  }  } catch (KeeperException e) {  System.out  .println("Keeper exception when instantiating queue: "  + e.toString());  } catch (InterruptedException e) {  System.out.println("Interrupted exception");  }  }  }  /**  * Add element to the queue.     *     * @param i  * @return  */  boolean produce(int i) throws KeeperException, InterruptedException{  ByteBuffer b = ByteBuffer.allocate(4);  byte[] value;  // Add child with value i  b.putInt(i);  value = b.array();  zk.create(root + "/element", value, Ids.OPEN_ACL_UNSAFE,  CreateMode.PERSISTENT_SEQUENTIAL);  return true;  }  /**  * Remove first element from the queue.     *     * @return     * @throws KeeperException  * @throws InterruptedException  */  int consume() throws KeeperException, InterruptedException{  int retvalue = -1;  Stat stat = null;  // Get the first element available  while (true) {  synchronized (mutex) {  List<String> list = zk.getChildren(root, true);  if (list.size() == 0) {  System.out.println("Going to wait");  mutex.wait();  } else {  Integer min = Integer.parseInt((list.get(0).substring(7)));  String minNode = list.get(0);  for(String s : list){  Integer tempValue = Integer.parseInt(s.substring(7));  //System.out.println("Temporary value: " + tempValue);  if(tempValue < min) {  min = tempValue;  minNode = s;  }  }  System.out.println("Temporary value: " + root + "/" + minNode);  byte[] b = zk.getData(root + "/" + minNode,  false, stat);  zk.delete(root + "/" + minNode, 0);  ByteBuffer buffer = ByteBuffer.wrap(b);  retvalue = buffer.getInt();  return retvalue;  }  }  }  }  
}