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 "/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。 */ 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; } } } }
}2.4 测试
生产消息： java SyncPrimitive qTest 192.168.206.100:2181 100 p
消费消息： java SyncPrimitive qTest 192.168.206.100:2181 100 c
2.5 结论
借助zookeeper实现消息队列的模拟。
