Java USES the example of a distributed lock implemented using zookeeper
- 2020-04-01 03:23:44
- OfStack
Distributed locks implemented using zookeeper
Distributed Lock, the implementation of the Lock interface
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";//The root
private String lockName;//Signs of competition for resources
private String waitNode;//Wait for the previous lock
private String myZnode;//The current lock
private CountDownLatch latch;//counter
private int sessionTimeout = 30000;
private List<Exception> exception = new ArrayList<Exception>();
public DistributedLock(String config, String lockName){
this.lockName = lockName;
//Create a connection to the server
try {
zk = new ZooKeeper(config, sessionTimeout, this);
Stat stat = zk.exists(root, false);
if(stat == null){
// create The root node
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);
}
}
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);//Waiting for the lock
}
} 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");
//Create temporary child nodes
myZnode = zk.create(root + "/" + lockName + splitStr, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(myZnode + " is created ");
//Fetch all child nodes
List<String> subNodes = zk.getChildren(root, false);
//Remove all locks for lockName
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))){
//If it is the smallest node, the lock is acquired
return true;
}
//If it is not the smallest node, find the node that is 1 less than itself
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);
// Determines whether a node smaller than itself exists , Not if it doesn't exist Waiting for the lock, Simultaneous registration listening
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);
}
}
}
Concurrent test tool
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;
public class ConcurrentTest {
private CountDownLatch startSignal = new CountDownLatch(1);//Start the valve
private CountDownLatch doneSignal = null;//End of the valve
private CopyOnWriteArrayList<Long> list = new CopyOnWriteArrayList<Long>();
private AtomicInteger err = new AtomicInteger();//Increasing atomic
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();
}
private void start(){
//Create threads and wait all threads at the valve
createThread();
//Open the valve
startSignal.countDown();//Decrement the latch count, and if the count reaches zero, all waiting threads are released
try {
doneSignal.await();//Wait for all threads to execute
} catch (InterruptedException e) {
e.printStackTrace();
}
//Compute execution time
getExeTime();
}
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();//Causes the current thread to wait until the latch counts backwards to zero
long start = System.currentTimeMillis();
task[j].run();
long end = (System.currentTimeMillis() - start);
list.add(end);
} catch (Exception e) {
err.getAndIncrement();//The equivalent of err++
}
doneSignal.countDown();
}
}).start();
}
}
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();
}
}
test
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);
}
}