哪些操作释放锁和不释放锁.死锁

心已赠人 2021-07-24 15:26 481阅读 0赞

# 哪些操作释放锁和不释放锁.死锁 #

## 释放锁的操作 ##

(1)当前线程的同步方法.同步代码块执行结束  
(2)当前线程在同步代码块.同步方法中遇到了break,return终止了同步代码块.同步方法的执行.  
(3)当前线程在同步代码块.同步方法中出现了未处理的Error或者Exception,导致当前线程异常结束  
(4)当前线程在同步代码块.同步方法中执行了锁对象的wait()方法,当前线程被挂起,并释放锁

## 不会释放锁的操作 ##

(1)线程执行同步代码块或同步方法时,程序调用Thread.sleep().Thread.yield()方法暂停当前线程的执行.

## sleep和wait方法的区别 ##

(1)sleep不会释放锁,wait方法会释放锁  
(2)sleep是Thread类,Thread.sleep(xx)  
wait是Object类声明的,同步锁/监视器调用

## 死锁 ##

**什么是死锁**  
当两个线程互相持有对方想要的锁,而进入循环等待.

尽量避免嵌套的代码块,这样能有效防止死锁

**一个产生死锁的代码**

/** * */
    package per.leiyustudy.thread.safe;
    
    /** * @author 雷雨 * * 测试死锁 * * 尽量避免嵌套的代码块,这样能有效防止死锁 * */
    public class TestDeadLock { 
    	public static void main(String[] args) { 
    		Object girl = new Object();
    		Object money = new Object();
    		Boy b = new Boy(girl,money);
    		Takes a = new Takes(girl, money);	
    		
    		b.start();
    		a.start();
    	}
    	
    
    }
    class Boy extends Thread{ 
    	private Object girl;
    	private Object money;
    	public Boy(Object girl,Object money){ 
    		super();
    		this.girl=girl;
    		this.money=money;		
    	}
    	public void run() { 
    		synchronized (money) { 
    			System.out.println("放了她,我给你500w");
    			synchronized (girl) { 
    			
    				System.out.println("得到了女朋友");
    			}
    			
    		}
    	}
    }
    class Takes extends Thread{ 
    	private Object girl;
    	private Object money;
    	public Takes(Object girl,Object money){ 
    		super();
    		this.girl=girl;
    		this.money=money;		
    	}
    	public void run() { 
    		synchronized (girl) { 
    			System.out.println("给我500w,我放了她");
    			synchronized (money) { 
    			
    				System.out.println("得到500w,放人");
    			}
    			
    		}
    	}
    }