java:lock锁

synchronized锁效率比较低,不方便扩展，不能自定义。于是从jdk1.5之后，就引入了lock锁。

lock可以手动上锁，手动释放锁，灵活性很高。

        Lock lock = new ReentrantLock();
		lock.lock(); 
		try{
			// 可能会出现线程安全的操作
		}finally{
			// 一定要在finally中释放锁
			lock.unlock();
		}

 lock锁例子

package com.baobaotao;

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

class Printer{
	// 打印机
	public String fileName;
	public String fileType;
	boolean flag = true;
	Lock lock = new ReentrantLock();
}

class Out extends Thread{
	Printer print;
	Condition newCon;
	
	public Out(Printer print, Condition newCon){
		this.print = print;
		this.newCon = newCon;
	}
	
	@Override
	public void run() {
		int count = 0;
	
		while(true){
				try{
					print.lock.lock();
					if(!print.flag){
						newCon.await(); 
					}
					
					
					if(count == 0){
						print.fileName = "三国演义";
						print.fileType = "pdf";
					}else{
						print.fileName = "红楼梦";
						print.fileType = "txt";
					}
					
					count = (count + 1)%2;
					print.flag = false;
					// 唤醒其他线程
					newCon.signal();
				}catch(Exception e){
					e.printStackTrace();
				}finally{
					System.out.println("Out--finally--unlock--");
					print.lock.unlock();
				}

			}
		}
}

class Input extends Thread{
	Printer print;
	Condition newCon;
	public Input(Printer print, Condition newCon){
		this.print = print;
		this.newCon = newCon;
	}
	
	@Override
	public void run() {
		while(true){
				try{
					print.lock.lock();
					if(print.flag){
						newCon.await(); 
					}
					
					System.out.println(print.fileName+", "+print.fileType);
					print.flag = true;
					newCon.signal();
					
				}catch(Exception e){
					e.printStackTrace();
				}finally{
					System.out.println("Input--finally--unlock--");
					print.lock.unlock();
				}
			}
		
	}
}

public class OutInputThread extends Thread{
	public static void main(String[] args){
		Printer print = new Printer();
		Condition newCon = print.lock.newCondition();
		
		Out out = new Out(print, newCon);
		Input input = new Input(print, newCon);
		out.start();
		input.start();
	}
}