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multithreaded lock

2022-07-31 18:33:00 【51CTO】

       
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多线程之锁_java

There are two types of thread locks: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,When many threads are contending for the same lock,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,To prevent forgetting to release the lock,一般在finally从句中释放.

SynchronizedWaiting time cannot be set,So if the waiting resource has been occupied,可能会出现死锁.

ReentrantLockbe more flexible,可以设置等待的时间,如果等待的时间到了,will do other tasks.

       
       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(member method or static method)
       
       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();
       
            }
       
         }
       
    }
       
 }
      
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       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)//Set the waiting time
       
      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(); 
       
    }
       
  }
       
}
      
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多线程之锁_锁_02

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