java多线程之测试并发（1）-监控Lock

一、Lock是java并发同步代码块的工具之一。我们可以通过监控Lock知道哪个线程获取到了锁，哪个线程释放了锁，那些线程正在等待锁。

二、监控Lock

package com.np.ota.test.synctest.lock;

import java.util.Collection;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 自定义Lock
 * @author luke
 */
public class MyLock extends ReentrantLock{

	private static final long serialVersionUID = 1L;
	
	public MyLock(){
		super(true);
	}
	
	public String getOwnerName(){
		if(this.getOwner() == null){
			return "none";
		}
		return this.getOwner().getName();
	}

	//Returns a collection containing threads that may be waiting to acquire this lock
	//Because the actual set of threads may change dynamically while constructing this result
	//获取等待该锁的所有线程集合，但结果不是绝对准确的
	public Collection<Thread> getThreads(){
		return this.getQueuedThreads();
	}
	
}

package com.np.ota.test.synctest.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;

public class Task implements Runnable{
	
	private Lock lock;
	
	public Task(Lock lock) {
		this.lock = lock;
	}

	@Override
	public void run() {
		for(int i = 0; i < 5; i++){
			lock.lock();
			System.out.println(Thread.currentThread().getName()+" get the lock");//获得锁的线程
			try {
				TimeUnit.MILLISECONDS.sleep(500);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}finally{
				System.out.println(Thread.currentThread().getName()+" free the lock");//线程释放锁
				lock.unlock();
			}
		}
	}

}

package com.np.ota.test.synctest.lock;

import java.util.Collection;
import java.util.concurrent.TimeUnit;

/**
 * 监控Lock
 * @author luke
 */
public class Main {

	public static void main(String[] args){

		//创建自定义锁，方便监控
		MyLock lock = new MyLock();
		
		//创建5个线程，并执行
		Thread[] threads = new Thread[5];
		for(int i = 0; i < 5; i++){
			Task task = new Task(lock);
			threads[i] = new Thread(task);
			threads[i].start();
		}
		
		//监控Lock
		for(int i = 0; i < 15; i++){
			System.out.println("***************************");
			System.out.println("Lock Owner : "+lock.getOwnerName());//锁的拥有者
			System.out.println("Lock queued Threads: "+lock.hasQueuedThreads());//是否有线程正在等待获取该锁
			if(lock.hasQueuedThreads()){
				System.out.println("waitting Lock queue length: "+lock.getQueueLength());//该瞬间等待该锁的线程数
				Collection<Thread> lockthreads = lock.getThreads();//遍历该瞬间等待该锁的线程
				for(Thread lockthread : lockthreads){
					System.out.println("waitting lock thread:"+lockthread.getName());
				}
			}
			System.out.println("lock fairness:"+lock.isFair());
			System.out.println("lock locked:"+lock.isLocked());
			System.out.println("***************************");
			try {
				TimeUnit.SECONDS.sleep(1);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		
	}

}

结果：

Thread-0 get the lock
***************************
Lock Owner : Thread-0
Lock queued Threads: true
waitting Lock queue length: 1
waitting lock thread:Thread-3
lock fairness:true
lock locked:true
***************************
Thread-0 free the lock
Thread-3 get the lock
Thread-3 free the lock
***************************
Lock Owner : Thread-3
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-0
waitting lock thread:Thread-4
waitting lock thread:Thread-2
waitting lock thread:Thread-1
lock fairness:true
lock locked:true
***************************
Thread-1 get the lock
Thread-1 free the lock
Thread-2 get the lock
***************************
Thread-2 free the lock
Lock Owner : Thread-2
Thread-4 get the lock
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-2
waitting lock thread:Thread-1
waitting lock thread:Thread-3
waitting lock thread:Thread-0
lock fairness:true
lock locked:true
***************************
Thread-4 free the lock
Thread-0 get the lock
Thread-0 free the lock
Thread-3 get the lock
***************************
Lock Owner : Thread-3
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-0
waitting lock thread:Thread-4
waitting lock thread:Thread-2
waitting lock thread:Thread-1
lock fairness:true
lock locked:true
***************************
Thread-3 free the lock
Thread-1 get the lock
Thread-1 free the lock
Thread-2 get the lock
***************************
Lock Owner : Thread-2
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-1
waitting lock thread:Thread-3
waitting lock thread:Thread-0
waitting lock thread:Thread-4
lock fairness:true
lock locked:true
***************************
Thread-2 free the lock
Thread-4 get the lock
Thread-4 free the lock
Thread-0 get the lock
***************************
Lock Owner : Thread-0
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-4
waitting lock thread:Thread-2
waitting lock thread:Thread-1
waitting lock thread:Thread-3
lock fairness:true
lock locked:true
***************************
Thread-0 free the lock
Thread-3 get the lock
Thread-3 free the lock
Thread-1 get the lock
***************************
Lock Owner : Thread-1
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-3
waitting lock thread:Thread-0
waitting lock thread:Thread-4
waitting lock thread:Thread-2
lock fairness:true
lock locked:true
***************************
Thread-1 free the lock
Thread-2 get the lock
Thread-2 free the lock
Thread-4 get the lock
***************************
Lock Owner : Thread-4
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-2
waitting lock thread:Thread-1
waitting lock thread:Thread-3
waitting lock thread:Thread-0
lock fairness:true
lock locked:true
***************************
Thread-4 free the lock
Thread-0 get the lock
Thread-0 free the lock
Thread-3 get the lock
***************************
Lock Owner : Thread-3
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-0
waitting lock thread:Thread-4
waitting lock thread:Thread-2
waitting lock thread:Thread-1
lock fairness:true
lock locked:true
***************************
Thread-3 free the lock
Thread-1 get the lock
Thread-1 free the lock
Thread-2 get the lock
***************************
Lock Owner : Thread-2
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-1
waitting lock thread:Thread-3
waitting lock thread:Thread-0
waitting lock thread:Thread-4
lock fairness:true
lock locked:true
***************************
Thread-2 free the lock
Thread-4 get the lock
Thread-4 free the lock
Thread-0 get the lock
***************************
Lock Owner : Thread-0
Lock queued Threads: true
waitting Lock queue length: 4
waitting lock thread:Thread-4
waitting lock thread:Thread-2
waitting lock thread:Thread-1
waitting lock thread:Thread-3
lock fairness:true
lock locked:true
***************************
Thread-0 free the lock
Thread-3 get the lock
Thread-3 free the lock
Thread-1 get the lock
***************************
Lock Owner : Thread-1
Lock queued Threads: true
waitting Lock queue length: 2
waitting lock thread:Thread-4
waitting lock thread:Thread-2
lock fairness:true
lock locked:true
***************************
Thread-1 free the lock
Thread-2 get the lock
Thread-2 free the lock
Thread-4 get the lock
***************************
Lock Owner : Thread-4
Lock queued Threads: false
lock fairness:true
lock locked:true
***************************
Thread-4 free the lock
***************************
Lock Owner : none
Lock queued Threads: false
lock fairness:true
lock locked:false
***************************
***************************
Lock Owner : none
Lock queued Threads: false
lock fairness:true
lock locked:false
***************************