使用synchronized和Lock对象获取对象锁_JAVA_编程开发_程序员俱乐部

在并发环境下，解决共享资源冲突问题时，可以考虑使用锁机制。
1.对象的锁
    所有对象都自动含有单一的锁。
    JVM负责跟踪对象被加锁的次数。如果一个对象被解锁，其计数变为0。在任务（线程）第一次给对象加锁的时候，计数变为1。每当这个相同的任务（线程）在此对象上获得锁时，计数会递增。
    只有首先获得锁的任务（线程）才能继续获取该对象上的多个锁。
    每当任务离开一个synchronized方法，计数递减，当计数为0的时候，锁被完全释放，此时别的任务就可以使用此资源。
2.synchronized同步块
    当使用同步块时，如果方法下的同步块都同步到一个对象上的锁，则所有的任务（线程）只能互斥的进入这些同步块。
    Resource1.java演示了三个线程（包括main线程）试图进入某个类的三个不同的方法的同步块中，虽然这些同步块处在不同的方法中，但由于是同步到同一个对象（当前对象 synchronized (this)），所以对它们的方法依然是互斥的。

package cn.java.loak;

import java.util.concurrent.TimeUnit;

public class Resource1 {

	public void f(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in f()");
		synchronized(this){
			for(int i=0;i<5; i++){
				System.out.println(Thread.currentThread().getName()+":synchronized in f()");
			try{
				TimeUnit.SECONDS.sleep(3);
			} catch (InterruptedException e){
				e.printStackTrace();
			}
			}
		}
	}
public void g(){
	System.out.println(Thread.currentThread().getName()+":not synchronized in g()");
	synchronized(this){
		for(int i=0;i<5;i++){
			System.out.println(Thread.currentThread().getName()+":synchronized in g()");
			try{
				TimeUnit.SECONDS.sleep(3);
			}catch (InterruptedException e){
				e.printStackTrace();
			}
		}
	}
}
public void h(){
	System.out.println(Thread.currentThread().getName()+":not synchronized in h()");
	synchronized(this){
		for(int i=0;i<5;i++){
			System.out.println(Thread.currentThread().getName()+":synchronized in h()");
			try{
				TimeUnit.SECONDS.sleep(3);
			} catch(InterruptedException e){
				e.printStackTrace();
			}
		}
	}
}

public static void main(String [] args){
	final Resource1 rs=new Resource1();
	new Thread(){
		public void run(){
			rs.f();
		}
	}.start();
	new Thread(){
		public void run(){
			rs.g();
		}
	}.start();
	
	rs.h();
	}
}

运行结果:
Thread-0:not synchronized in f()
Thread-0:synchronized in f()
main:not synchronized in h()
Thread-1:not synchronized in g()
Thread-0:synchronized in f()
Thread-0:synchronized in f()
Thread-0:synchronized in f()
Thread-0:synchronized in f()
Thread-1:synchronized in g()
Thread-1:synchronized in g()
Thread-1:synchronized in g()
Thread-1:synchronized in g()
Thread-1:synchronized in g()
main:synchronized in h()
main:synchronized in h()
main:synchronized in h()
main:synchronized in h()
main:synchronized in h()

2.2 同步到多个对象锁
    Resource2.java演示了三个线程（包括main线程）试图进入某个类的三个不同的方法的同步块中，这些同步块处在不同的方法中，并且是同步到三个不同的对象（synchronized (this)，synchronized (syncObject1)，synchronized (syncObject2)），所以对它们的方法中的临界资源访问是独立的。

package cn.java.loak;

import java.util.concurrent.TimeUnit;

public class Resource2 {
	private Object syncObject1=new Object();
	private Object syncObject2=new Object();
	
	public void f(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in f()");
		synchronized(this){
			for(int i=0;i<5;i++){
				System.out.println(Thread.currentThread().getName()+":synchronized in f()");
				try{
					TimeUnit.SECONDS.sleep(3);
				} catch (InterruptedException e){
					e.printStackTrace();
				}
			}
		}
	}
	
	public void g(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in g()");
		synchronized (syncObject1){
			for(int i=0;i<5;i++){
				System.out.println(Thread.currentThread().getName()+":synchronized in g()");
				try{
					TimeUnit.SECONDS.sleep(3);
				} catch(InterruptedException e){
					e.printStackTrace();
				}
			}
		}
	}
	
	public void h(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in h()");
		synchronized(syncObject2){
			for(int i=0;i<5;i++){
				System.out.println(Thread.currentThread().getName()+":synchronized in h()");
				try{
					TimeUnit.SECONDS.sleep(3);
		
				} catch(InterruptedException e){
					e.printStackTrace();
				}
			}
		}
	}
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		final Resource2 rs=new Resource2();
		
		new Thread(){
			public void run(){
				rs.f();
			}
		}.start();
		
		new Thread(){
			public void run(){
				rs.g();
				
			}
		}.start();
		
		rs.h();
	}

}

运行结果
Thread-0:not synchronized in f()
Thread-0:synchronized in f()
main:not synchronized in h()
main:synchronized in h()
Thread-1:not synchronized in g()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()

3.Lock对象锁
    除了使用synchronized外，还可以使用Lock对象来创建临界区。Resource3.java的演示效果同Resource1.java；Resource4.java的演示效果同Resource2.java。

package cn.java.loak;

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

public class Resource3 {
	private Lock lock = new ReentrantLock();
	
	public void f(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in f()");
		lock.lock();
		try{
			for (int i=0;i<5;i++){
				System.out.println(Thread.currentThread().getName()+"synchronized in f()");
				try{
					TimeUnit.SECONDS.sleep(3);
				}catch(InterruptedException e){
					e.printStackTrace();
				}
			}	
		}finally{
			lock.unlock();
		}
	}

public void g(){
	System.out.println(Thread.currentThread().getName()+":not synchronized in g()");
	lock.lock();
	try{
		for (int i=0;i<5;i++){
			System.out.println(Thread.currentThread().getName()+"synchronized in g()");
			try{
				TimeUnit.SECONDS.sleep(3);
			}catch(InterruptedException e){
				e.printStackTrace();
			}
		}	
	}finally{
		lock.unlock();
	}
}
public void h(){
	System.out.println(Thread.currentThread().getName()+":not synchronized in h()");
	lock.lock();
	try{
		for (int i=0;i<5;i++){
			System.out.println(Thread.currentThread().getName()+"synchronized in h()");
			try{
				TimeUnit.SECONDS.sleep(3);
			}catch(InterruptedException e){
				e.printStackTrace();
			}
		}	
	}finally{
		lock.unlock();
	}
}

public static void main(String[] args){
	final Resource3 rs=new Resource3();
	
	new Thread(){
		public void run(){
			rs.f();
		}
	}.start();
	
	new Thread(){
		public void run(){
			rs.g();
		}
	}.start();
	
	rs.h();
}
}

运行结果
Thread-0:not synchronized in f()
Thread-0synchronized in f()
main:not synchronized in h()
Thread-1:not synchronized in g()
Thread-0synchronized in f()
Thread-0synchronized in f()
Thread-0synchronized in f()
Thread-0synchronized in f()
mainsynchronized in h()
mainsynchronized in h()
mainsynchronized in h()
mainsynchronized in h()
mainsynchronized in h()
Thread-1synchronized in g()
Thread-1synchronized in g()
Thread-1synchronized in g()
Thread-1synchronized in g()
Thread-1synchronized in g()

package cn.java.loak;

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

public class Resource4 {
	private Lock lock1=new ReentrantLock();
	private Lock lock2=new ReentrantLock();
	private Lock lock3=new ReentrantLock();
	
	public void f(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in f()");
		lock1.lock();
		try{
			for(int i=0;i<5;i++){
				System.out.println(Thread.currentThread().getName()+":synchronized in f()");
			try{
				TimeUnit.SECONDS.sleep(3);
			}catch(InterruptedException e){
				e.printStackTrace();
			}
			
		}
	}finally{
		lock1.unlock();
	}
}
	public void g(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in g()");
		lock2.lock();
		try{
			for(int i=0;i<5;i++){
				System.out.println(Thread.currentThread().getName()+":synchronized in g()");
			try{
				TimeUnit.SECONDS.sleep(3);
			}catch(InterruptedException e){
				e.printStackTrace();
			}
			
		}
	}finally{
		lock2.unlock();
	}
}
	public void h(){
		System.out.println(Thread.currentThread().getName()+":not synchronized in h()");
		lock3.lock();
		try{
			for(int i=0;i<5;i++){
				System.out.println(Thread.currentThread().getName()+":synchronized in h()");
			try{
				TimeUnit.SECONDS.sleep(3);
			}catch(InterruptedException e){
				e.printStackTrace();
			}
			
		}
	}finally{
		lock3.unlock();
	}
}
	public static void main(String[] args){
		final Resource4 rs=new Resource4();
		
		new Thread(){
			public void run(){
				rs.f();
			}
		}.start();
	
		new Thread(){
			public void run(){
				rs.g();
			}
		}.start();
		
		rs.h();
	}
}

运行结果
Thread-0:not synchronized in f()
Thread-0:synchronized in f()
main:not synchronized in h()
main:synchronized in h()
Thread-1:not synchronized in g()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()
Thread-0:synchronized in f()
main:synchronized in h()
Thread-1:synchronized in g()