Zookeeper Implement barrier _barrier

Zookeeper Implement barrier _barrier

According to the official website of the demo, their own understanding, add the corresponding comments, here to put the code out, such as the next,

Barrier

package com.usfot;import org.apache.zookeeper.createmode;import  org.apache.zookeeper.keeperexception;import org.apache.zookeeper.watchedevent;import  org.apache.zookeeper.watcher;import org.apache.zookeeper.zoodefs;import  org.apache.zookeeper.zookeeper;import org.apache.zookeeper.data.stat;import java.util.list;/**  *  inherits watcher to achieve synchronous processing between different tasks in the distributed environment (using the reverse push of the watcher mechanism).  *  the triggering of the event causes the thread to handle it accordingly, thus avoiding the unnecessary while (true), which causes the CPU to spin out of the loop.  */public class barrier implements watcher {    private  static final String addr =  "127.0.0.1:2181";     private  ZooKeeper zk = null;    private Integer mutex;     private int size = 0;    private String root;     public barrier (string root, int size)  {        this.root = root;         this.size = size;        try {             zk = new zookeeper (addr, 10  * 1000, this);             mutex  = new integer ( -1);             stat  s = zk.exists (Root, false);             if  (s == null)  {                 zk.create (Root, new byte[0], zoodefs.ids.open_acl_unsafe,  createmode.persistent);            }         } catch  (exception e)  {             e.printstacktrace ();        }     }    /**     *  Wake up threads waiting on a mutex when the event is triggered       *  as long as the data of the node on the ZK server changes (no matter which zk client changes the data),     *  This will receive the corresponding event to wake up the corresponding thread and make the appropriate processing      *     *  @param   Event     */    public synchronized void process ( watchedevent event)  {        synchronized  (mutex)   {            mutex.notify ();         }    }    /**      *  when creating a new Znode, first hold the mutex supervisorTo enter the synchronization code block.      *  when a Znode event occurs, the process is triggered to wake up the thread waiting on the mutex.      *  determines the number of nodes created through the while loop, and the Enter method executes when the number of nodes is greater than the set value.      *     *  @param  name      *  @return      *  @throws  exception     * /    public boolean enter (String name)  throws exception {         zk.create (root +  "/"  + name, new  byte[0], zoodefs.ids.open_acl_unsafe, createmode.ephemeral);         while  (True)  {             synchronized  (Mutex)  {                 list<string> list = zk.getchIldren (root, true);                 if  (List.size ()  < size)  {                     mutex.wait ();                 } else {                     return  true;                }             }         }    }    /**     * . For the Leave method, when Delete znode, triggers the event, which wakes up the waiting thread on the mutex, through the while loop      *  determines the number of nodes, When the node is all removed, the Leave method ends.      *  so that the entire add delete Znode thread ends      *     *   @param  name     *  @return      *  @throws  KeeperException     *  @throws  InterruptedException      */    public boolean leave (String name)  throws  Keeperexception, interruptedexception {        zk.delete ( root +  "/"  + name, 0);        while  ( true)  {            synchronized  (mutex)  {                list <string> list = zk.getchildren (root, true);                 if  (List.size ()  > 0)  {                     mutex.wait ();                 } else {                      return true;                 }            }         }    }}

Barriertest

package com.usfot;import java.util.random;public class barriertest {     /**     *  starts three threads and corresponds to three ZK clients      *      *  @param  args     *  @throws  exception      */    public static void main (String  Args[])  throws Exception {        for  (int i  = 0; i < 3; i++)  {             process p = new process ("thread-"  + i, new  Barrier ("/test_node",  3));             p.start ();         }    }}class process extends  thread {    private string name;    private barrier barrier;     public process (String name, barrier barrier)  {         this.name = name;         this.barrier = barrier;    }     @Override      public void run ()  {        try {             barrier.enter (name);             system.out.println (name +  " enter");             thread.sleep (1000 + new random (). Nextint (+));             barrier.leave (name);             system.out.println (name +  " leave");         } catch  (exception e)  {             e.printstacktrace ();         }     }}

Execute this procedure, as below,

Thread-1 enterThread-2 enterThread-0 enterThread-0 leaveThread-1 leaveThread-2 leaveprocess finished with exit code 0

Open ZK's client, as below,

[Zk:localhost:2181 (CONNECTED) 8] LS/[testrootpath, Test_node, Mynode, zookeeper, zk_test0000000005, Zk_test][zk:  localhost:2181 (CONNECTED) 9] Get/test_nodeczxid = 0x800000051ctime = Tue Mar 19:08:49 CST 2015mZxid = 0x800000051mtime  = Tue Mar 19:08:49 CST 2015pZxid = 0x800000062cversion = 12dataVersion = 0aclVersion = 0ephemeralOwner = 0x0datalength = 0numChildren = 0[zk:localhost:2181 (CONNECTED) ls/test_node[][zk:localhost:2181 (CONNECTED) 11]

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Zookeeper Implement barrier _barrier