线程同步锁和异步锁的几种方式

女爷i 2023-06-21 04:56 6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][]

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