线程同步锁和异步锁的几种方式

女爷i 2023-06-21 04:56 31阅读 0赞

同步锁：当在一个java虚拟机多个线程操作一个变量的时候就会出现线程安全问题，这个时候就会用到同步锁。

同步锁的解决方式：

先看下一个线程异常的售票

public class ThreadSafe { 
       
       public static void main(String[] args) { 
       MyThread t1 = new MyThread( "窗口一"); 
       MyThread t2 = new MyThread( "窗口一"); 
       
       t1.start(); 
       t2.start(); 
       
       try { 
       t1.join(); 
       t2.join(); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       
       } 
       
       static class MyThread extends Thread{ 
       
       private static int count = 10; 
       
       public MyThread(String name) { 
       super(name); 
       } 
       
       @Override 
       public void run() { 
       while(count > 0) { 
       System.out.println(Thread.currentThread().getName()+ "售出："+(count--) + " 票"); 
       try { 
       Thread.sleep( 1000); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       } 
       } 
       }

synchronized 解决的三种方式：1）使用synchronized 静态代码块    2）synchronized 同步方法  3）synchronized 同步类

public class ThreadSafe { 
       
       public static Object obj = new Object(); 
       
       public static void main(String[] args) { 
       MyThread t1 = new MyThread( "窗口一"); 
       MyThread t2 = new MyThread( "窗口一"); 
       
       t1.start(); 
       t2.start(); 
       
       try { 
       t1.join(); 
       t2.join(); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       
       static class MyThread extends Thread{ 
       
       private static int count = 10; 
       
       public MyThread(String name) { 
       super(name); 
       } 
       
       @Override 
       public void run() { 
       while(count > 0) { 
       //静态代码块锁，定义同一个对象 
       synchronized (obj) { 
       System.out.println(Thread.currentThread().getName()+ "售出："+(count--) + " 票"); 
       } 
       try { 
       Thread.sleep( 1000); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       } 
       } 
       }

//使用synchronized 定义的方法锁 
       public class ThreadSafe1 { 
       
       public static Object obj = new Object(); 
       
       public static void main(String[] args) { 
       //这个地方必须是对同一个对象进行操作 
       MyThread myThread = new MyThread(); 
       Thread t1 = new Thread(myThread, "窗口一"); 
       Thread t2 = new Thread(myThread, "窗口二"); 
       
       t1.start(); 
       t2.start(); 
       
       try { 
       t1.join(); 
       t2.join(); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       
       static class MyThread implements Runnable{ 
       
       private static int count = 10; 
       
       //方法锁 
       public synchronized void increse() { 
       System.out.println(Thread.currentThread().getName()+ "售出："+(count--) + " 票"); 
       } 
       
       @Override 
       public void run() { 
       while(count > 0) { 
       increse(); 
       try { 
       Thread.sleep( 1000); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       } 
       } 
       }

//使用类锁 
       public class ThreadSafe2 { 
       
       public static void main(String[] args) { 
       MyThread t1 = new MyThread( "窗口一"); 
       MyThread t2 = new MyThread( "窗口一"); 
       
       t1.start(); 
       t2.start(); 
       
       try { 
       t1.join(); 
       t2.join(); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       
       static class MyThread extends Thread{ 
       
       private static int count = 10; 
       
       public MyThread(String name) { 
       super(name); 
       } 
       
       public static synchronized void increase() { 
       System.out.println(Thread.currentThread().getName()+ "售出："+(count--) + " 票"); 
       } 
       
       @Override 
       public void run() { 
       while(count > 0) { 
       //静态代码块锁，定义同一个对象 
       increase(); 
       try { 
       Thread.sleep( 1000); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       } 
       } 
       }

2.使用lock的解决方式

//使用类锁 
       public class ThreadSafe3 { 
       
       public static Lock lock = new ReentrantLock(); 
       
       public static void main(String[] args) { 
       MyThread t1 = new MyThread( "窗口一"); 
       MyThread t2 = new MyThread( "窗口二"); 
       
       t1.start(); 
       t2.start(); 
       
       try { 
       t1. join(); 
       t2. join(); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       
       static class MyThread extends Thread{ 
       
       private static int count = 10; 
       
       public MyThread(String name) { 
       super(name); 
       } 
       
       public static void increase() { 
       lock. lock(); 
       try { 
       System. out.println(Thread.currentThread().getName()+ "售出："+(count--) + " 票"); 
       } catch (Exception e) { 
       e.printStackTrace(); 
       } finally { 
       lock.unlock(); 
       } 
       
       } 
       
       @ Override 
       public void run( ) { 
       while(count > 0) { 
       //静态代码块锁，定义同一个对象 
       increase(); 
       try { 
       Thread.sleep( 1000); 
       } catch (InterruptedException e) { 
       e.printStackTrace(); 
       } 
       } 
       } 
       } 
       }

异步锁：就是多个java 虚拟机或者说是服务器，操作同一个变量是，会出现线程安全问题，使用需要使用异步锁来处理。

1）数据库  乐观锁 悲观锁 唯一标示  不推荐使用，容易出现锁表，出现死锁。

2）Redis 分布式锁 ，就是设置一个flag标识，当一个服务拿到锁以后立即把对应的标识设置为false  用完后释放锁，并把标识修改为true 详见如下：

![70][]

3）使用dubbo  zookeeper (共享锁，排它锁)，这里就根据自己的情况，共享锁还是会出现阻塞的情况，排它锁就是会生成很多临时的节点，谁先获取最小的序号标识谁就先获取到锁。

![70 1][]

*      <li class="tool-item tool-active is-like "><a href="javascript:;"><svg class="icon" aria-hidden="true">
                                <use xlink:href="#csdnc-thumbsup"></use>
                            </svg><span class="name">点赞</span>
                            <span class="count"></span>
                            </a></li>
                            <li class="tool-item tool-active is-collection "><a href="javascript:;" data-report-click="{"mod":"popu_824"}"><svg class="icon" aria-hidden="true">
                                <use xlink:href="#icon-csdnc-Collection-G"></use>
                            </svg><span class="name">收藏</span></a></li>
                            <li class="tool-item tool-active is-share"><a href="javascript:;"><svg class="icon" aria-hidden="true">
                                <use xlink:href="#icon-csdnc-fenxiang"></use>
                            </svg>分享</a></li>
                            
                                                    
                                                    <li class="tool-item tool-more">
                                <a>
                                <svg t="1575545411852" class="icon" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5717" xmlns:xlink="http://www.w3.org/1999/xlink" width="200" height="200"><defs><style type="text/css"></style></defs><path d="M179.176 499.222m-113.245 0a113.245 113.245 0 1 0 226.49 0 113.245 113.245 0 1 0-226.49 0Z" p-id="5718"></path><path d="M509.684 499.222m-113.245 0a113.245 113.245 0 1 0 226.49 0 113.245 113.245 0 1 0-226.49 0Z" p-id="5719"></path><path d="M846.175 499.222m-113.245 0a113.245 113.245 0 1 0 226.49 0 113.245 113.245 0 1 0-226.49 0Z" p-id="5720"></path></svg>
                                </a>
                                <ul class="more-box">
                                    <li class="item"><a class="article-report">文章举报</a></li>
                                </ul>
                            </li>
                                                </ul>
                    </div>
                                </div>
                <div class="person-messagebox">
                    <div class="left-message"><a href="https://blog.csdn.net/qq_18430613">
                        <img src="https://profile.csdnimg.cn/E/7/D/3_qq_18430613" class="avatar_pic" username="qq_18430613">
                                                <img src="https://g.csdnimg.cn/static/user-reg-year/1x/5.png" class="user-years">
                                        </a></div>
                    <div class="middle-message">
                                            <div class="title"><span class="tit"><a href="https://blog.csdn.net/qq_18430613" data-report-click="{"mod":"popu_379"}" target="_blank">qq_18430613</a></span>
                                                </div>
                        <div class="text"><span>发布了11 篇原创文章</span> · <span>获赞 0</span> · <span>访问量 1万+</span></div>
                    </div>
                                    <div class="right-message">
                                                <a href="https://im.csdn.net/im/main.html?userName=qq_18430613" target="_blank" class="btn btn-sm btn-red-hollow bt-button personal-letter">私信
                            </a>
                                                                <a class="btn btn-sm  bt-button personal-watch" data-report-click="{"mod":"popu_379"}">关注</a>
                                        </div>
                                </div>
            </div>

[70]: https://img-blog.csdn.net/20180910105932451?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzE4NDMwNjEz/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70
[70 1]: https://img-blog.csdn.net/201809101110500?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzE4NDMwNjEz/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70