多线程之锁

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线程锁分两种:内置锁(synchronized)和显式锁(ReentrantLock)

简单对比:

主要相同点：Lock能完成synchronized所实现的所有功能
主要不同点：Lock有比synchronized更精确的线程语义和更好的性能，当许多线程都在争用同一个锁时，使用 ReentrantLock 的总体开支通常要比 synchronized 少得多。
synchronized会自动释放锁，而Lock一定要求程序员手工释放，为了防止忘记释放锁，一般在finally从句中释放。

Synchronized不能设置等待时间，所以如果等待的资源一直被占用，可能会出现死锁.

ReentrantLock会灵活一点，可以设置等待的时间，如果等待的时间到了，就会去做其它的任务.

package com.wowowo.lock;
 
public class SellTicket implements Runnable {
     
    private static int tickets=100;
     
     
    public void run()
    {
         while(true)
         {
              
             /*
             //隐士锁 内置锁 方式1 锁住代码块
             synchronized (this) {                
             
                 if(tickets>0)
                 {                 
                     System.out.println(Thread.currentThread().getName()+"售出第..."+tickets+"...张票");
                      
                     tickets--;
                      
                     try {
                        Thread.sleep(10); //休眠 10毫秒
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                      
                 }
                 
             }*/
            //方式 2
             sellTicket();   
         }
         
    }
     
    //方式2 锁住方法(成员方法或静态方法)
    public synchronized void sellTicket()
    {        
         if(tickets>0)
         {                 
             System.out.println(Thread.currentThread().getName()+"售出第..."+tickets+"...张票");
              
             tickets--;
              
             try {
                Thread.sleep(10); //休眠 10毫秒
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
              
         }
    }
  
 
}

package com.wowowo.lock;
 
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
 
public class SellTicket2 implements Runnable {
 
    private static int tickets=100;
     
    //显示锁
    private Lock lock=new ReentrantLock();
     
     
    @Override
    public void run() {
        // TODO Auto-generated method stub
         
        while(true)
        {
            lock.lock(); //上锁
             
            //lock.tryLock(arg0, arg1)//设置等待的时间的
            if(tickets>0)
            {
                System.out.println(Thread.currentThread().getName()+"售出第.."+tickets+"..张票");
                 
                tickets--;
                 
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }               
            }           
            //开锁
            lock.unlock(); 
             
        }
         
    }
     
     
 
}

package com.wowowo.lock;
 
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class Test {
 
    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
 
        //创建线程池对象
         ExecutorService pool= Executors.newFixedThreadPool(3);
          
         //创建售票任务 对象
         SellTicket2 sellTicket=new SellTicket2();
          
         pool.submit(sellTicket);
          
         pool.submit(sellTicket);
          
         pool.submit(sellTicket);
         
         
    }
 
}