分布式并发锁处理

    采用悲观锁来实现同步
    在sql语句后加 for update就加上了锁，在查询的时候进行加锁，在加锁后不能进行查询。提交时候后其他人才能查询。
    public static int generate(String tableName){
            //使用数据库的悲观锁for update
            String sql = "select value from t_table_id where table_name=? for update";
            Connection conn = null;
            PreparedStatement pstmt = null;
            ResultSet rs = null;
            int value = 0;
            try{
                conn = DbUtil.getConnection();
                //设置自动提交为false
                DbUtil.beginTransaction(conn);
                pstmt = conn.prepareStatement(sql);
                pstmt.setString(1, tableName);
                rs = pstmt.executeQuery();
                rs.next();
    //            if(!rs.next()){
    //                throw new RuntimeException();
    //            }
                value = rs.getInt("value");
                value++;
                modifyValueField(conn,tableName,value);
                //提交事务
                DbUtil.commitTransaction(conn);
            }catch(Exception e){
                e.printStackTrace();
                //回滚事务
                DbUtil.rollbackTranscation(conn);
                throw new RuntimeException();
            }finally{
                DbUtil.close(rs);
                DbUtil.close(pstmt);
                DbUtil.resetConnection(conn);
                DbUtil.close(conn);
            }
            return value;
        }

使用zookeeper实现的分布式锁

分布式锁，实现了Lock接口


复制代码 代码如下:


package com.concurrent;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

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;

/**
   DistributedLock lock = null;
 try {
  lock = new DistributedLock("127.0.0.1:2182","test");
  lock.lock();
  //do something...
 } catch (Exception e) {
  e.printStackTrace();
 } 
 finally {
  if(lock != null)
   lock.unlock();
 }
 * @author xueliang
 *
 */
public class DistributedLock implements Lock, Watcher{
 private ZooKeeper zk;
 private String root = "/locks";//根
 private String lockName;//竞争资源的标志
 private String waitNode;//等待前一个锁
 private String myZnode;//当前锁
 private CountDownLatch latch;//计数器
 private int sessionTimeout = 30000;
 private List<Exception> exception = new ArrayList<Exception>();

 /**
  * 创建分布式锁,使用前请确认config配置的zookeeper服务可用
  * @param config 127.0.0.1:2181
  * @param lockName 竞争资源标志,lockName中不能包含单词lock
  */
 public DistributedLock(String config, String lockName){
  this.lockName = lockName;
  // 创建一个与服务器的连接
   try {
   zk = new ZooKeeper(config, sessionTimeout, this);
   Stat stat = zk.exists(root, false);
   if(stat == null){
    // 创建根节点
    zk.create(root, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT); 
   }
  } catch (IOException e) {
   exception.add(e);
  } catch (KeeperException e) {
   exception.add(e);
  } catch (InterruptedException e) {
   exception.add(e);
  }
 }

 /**
  * zookeeper节点的监视器
  */
 public void process(WatchedEvent event) {
  if(this.latch != null) {  
            this.latch.countDown();  
        }
 }

 public void lock() {
  if(exception.size() > 0){
   throw new LockException(exception.get(0));
  }
  try {
   if(this.tryLock()){
    System.out.println("Thread " + Thread.currentThread().getId() + " " +myZnode + " get lock true");
    return;
   }
   else{
    waitForLock(waitNode, sessionTimeout);//等待锁
   }
  } catch (KeeperException e) {
   throw new LockException(e);
  } catch (InterruptedException e) {
   throw new LockException(e);
  } 
 }

 public boolean tryLock() {
  try {
   String splitStr = "_lock_";
   if(lockName.contains(splitStr))
    throw new LockException("lockName can not contains \\u000B");
   //创建临时子节点
   myZnode = zk.create(root + "/" + lockName + splitStr, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);
   System.out.println(myZnode + " is created ");
   //取出所有子节点
   List<String> subNodes = zk.getChildren(root, false);
   //取出所有lockName的锁
   List<String> lockObjNodes = new ArrayList<String>();
   for (String node : subNodes) {
    String _node = node.split(splitStr)[0];
    if(_node.equals(lockName)){
     lockObjNodes.add(node);
    }
   }
   Collections.sort(lockObjNodes);
   System.out.println(myZnode + "==" + lockObjNodes.get(0));
   if(myZnode.equals(root+"/"+lockObjNodes.get(0))){
    //如果是最小的节点,则表示取得锁
             return true;
         }
   //如果不是最小的节点，找到比自己小1的节点
   String subMyZnode = myZnode.substring(myZnode.lastIndexOf("/") + 1);
   waitNode = lockObjNodes.get(Collections.binarySearch(lockObjNodes, subMyZnode) - 1);
  } catch (KeeperException e) {
   throw new LockException(e);
  } catch (InterruptedException e) {
   throw new LockException(e);
  }
  return false;
 }

 public boolean tryLock(long time, TimeUnit unit) {
  try {
   if(this.tryLock()){
    return true;
   }
         return waitForLock(waitNode,time);
  } catch (Exception e) {
   e.printStackTrace();
  }
  return false;
 }

 private boolean waitForLock(String lower, long waitTime) throws InterruptedException, KeeperException {
        Stat stat = zk.exists(root + "/" + lower,true);
        //判断比自己小一个数的节点是否存在,如果不存在则无需等待锁,同时注册监听
        if(stat != null){
         System.out.println("Thread " + Thread.currentThread().getId() + " waiting for " + root + "/" + lower);
         this.latch = new CountDownLatch(1);
         this.latch.await(waitTime, TimeUnit.MILLISECONDS);
         this.latch = null;
        }
        return true;
    }

 public void unlock() {
  try {
   System.out.println("unlock " + myZnode);
   zk.delete(myZnode,-1);
   myZnode = null;
   zk.close();
  } catch (InterruptedException e) {
   e.printStackTrace();
  } catch (KeeperException e) {
   e.printStackTrace();
  }
 }

 public void lockInterruptibly() throws InterruptedException {
  this.lock();
 }

 public Condition newCondition() {
  return null;
 }

 public class LockException extends RuntimeException {
  private static final long serialVersionUID = 1L;
  public LockException(String e){
   super(e);
  }
  public LockException(Exception e){
   super(e);
  }
 }

}



并发测试工具


复制代码 代码如下:


package com.concurrent;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;

/**
  ConcurrentTask[] task = new ConcurrentTask[5];
  for(int i=0;i<task.length;i++){
      task[i] = new ConcurrentTask(){
    public void run() {
     System.out.println("==============");

    }};
  }
  new ConcurrentTest(task);
 * @author xueliang
 *
 */
public class ConcurrentTest {
 private CountDownLatch startSignal = new CountDownLatch(1);//开始阀门
 private CountDownLatch doneSignal = null;//结束阀门
 private CopyOnWriteArrayList<Long> list = new CopyOnWriteArrayList<Long>();
 private AtomicInteger err = new AtomicInteger();//原子递增
 private ConcurrentTask[] task = null;

 public ConcurrentTest(ConcurrentTask... task){
  this.task = task;
  if(task == null){
   System.out.println("task can not null");
   System.exit(1);
  }
  doneSignal = new CountDownLatch(task.length);
  start();
 }
 /**
  * @param args
  * @throws ClassNotFoundException 
  */
 private void start(){
  //创建线程，并将所有线程等待在阀门处
  createThread();
  //打开阀门
  startSignal.countDown();//递减锁存器的计数，如果计数到达零，则释放所有等待的线程
  try {
   doneSignal.await();//等待所有线程都执行完毕
  } catch (InterruptedException e) {
   e.printStackTrace();
  }
  //计算执行时间
  getExeTime();
 }
 /**
  * 初始化所有线程，并在阀门处等待
  */
 private void createThread() {
  long len = doneSignal.getCount();
  for (int i = 0; i < len; i++) {
   final int j = i;
   new Thread(new Runnable(){
    public void run() {
     try {
      startSignal.await();//使当前线程在锁存器倒计数至零之前一直等待
      long start = System.currentTimeMillis();
      task[j].run();
      long end = (System.currentTimeMillis() - start);
      list.add(end);
     } catch (Exception e) {
      err.getAndIncrement();//相当于err++
     } 
     doneSignal.countDown();
    }
   }).start();
  }
 }
 /**
  * 计算平均响应时间
  */
 private void getExeTime() {
  int size = list.size();
  List<Long> _list = new ArrayList<Long>(size);
  _list.addAll(list);
  Collections.sort(_list);
  long min = _list.get(0);
  long max = _list.get(size-1);
  long sum = 0L;
  for (Long t : _list) {
   sum += t;
  }
  long avg = sum/size;
  System.out.println("min: " + min);
  System.out.println("max: " + max);
  System.out.println("avg: " + avg);
  System.out.println("err: " + err.get());
 }

 public interface ConcurrentTask {
  void run();
 }

}



测试


复制代码 代码如下:


package com.concurrent;

import com.concurrent.ConcurrentTest.ConcurrentTask;

public class ZkTest {
 public static void main(String[] args) {
  Runnable task1 = new Runnable(){
   public void run() {
    DistributedLock lock = null;
    try {
     lock = new DistributedLock("127.0.0.1:2182","test1");
     //lock = new DistributedLock("127.0.0.1:2182","test2");
     lock.lock();
     Thread.sleep(3000);
     System.out.println("===Thread " + Thread.currentThread().getId() + " running");
    } catch (Exception e) {
     e.printStackTrace();
    } 
    finally {
     if(lock != null)
      lock.unlock();
    }

   }

  };
  new Thread(task1).start();
  try {
   Thread.sleep(1000);
  } catch (InterruptedException e1) {
   e1.printStackTrace();
  }
  ConcurrentTask[] tasks = new ConcurrentTask[60];
  for(int i=0;i<tasks.length;i++){
   ConcurrentTask task3 = new ConcurrentTask(){
    public void run() {
     DistributedLock lock = null;
     try {
      lock = new DistributedLock("127.0.0.1:2183","test2");
      lock.lock();
      System.out.println("Thread " + Thread.currentThread().getId() + " running");
     } catch (Exception e) {
      e.printStackTrace();
     } 
     finally {
      lock.unlock();
     }

    }
   };
   tasks[i] = task3;
  }
  new ConcurrentTest(tasks);
 }
}