同步实现同步的三种方式

深藏阁楼爱情的钟 2021-10-18 10:30 404阅读 0赞

/**
     * 多线程共享数据：多个线程有可能同时处理同一个资源
     * 同步：多个线程在同一时间段内只能有一个线程执行指定代码，其它线程要等此线程执行完成之后才可以继续执行
     */
    /**
     * 1.多线程共享数据时会发生线程不安全的情况
     * 2.多线程共享数据必须使用同步
     * 3.实现同步的三种方式：
     *     1)同步代码块
     *          synchronized（要同步的对象）{   要同步的操作  }
     *     2）同步方法
     *          private synchronized void method(){ 要同步的操作 }
     *     3) 使用Lock(更灵活的代码控制)
     *   使用同步可以解决安全问题，但同时会牺牲性能，所以同步的代码块要尽量保持简短，
     *   把不随数据变化的相关代码移除同步快，不要阻塞
     */

### <1>使用Lock ###

package com.vince;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class ThreadDemo4 {
        public static void main(String[] args) {
           MyRunnable5 mr5 = new MyRunnable5();
           Thread t1 = new Thread(mr5);
           Thread t2 = new Thread(mr5);
           t1.start();
           t2.start();
        }
    }
    
    class MyRunnable5 implements Runnable{
        private int ticket = 10;//售票
        @Override
        public void run() {
           for(int i =0; i < 300; i++){
                  method2();
           }
        }
       //互斥锁
        ReentrantLock lock = new ReentrantLock();
        //Lock实现同步
        private void method2(){
            lock.lock();//锁
            try {
                if (ticket > 0) {
                    ticket--;
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("您购买的票已剩余" + ticket + "张");
                }
            }finally {
                lock.unlock();//释放锁
            }
          }
    }

### <2> 同步方法 ###

package com.vince;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class ThreadDemo4 {
        public static void main(String[] args) {
           MyRunnable5 mr5 = new MyRunnable5();
           Thread t1 = new Thread(mr5);
           Thread t2 = new Thread(mr5);
           t1.start();
           t2.start();
        }
    }
    
    class MyRunnable5 implements Runnable{
        private int ticket = 10;//售票
        @Override
        public void run() {
           for(int i =0; i < 300; i++){
                method();
           }
        }
       //同步方法：同步的对象是当前对象(this)
        private synchronized void method(){
                if(ticket > 0){
                      ticket--;
                      try {
                          Thread.sleep(500);
                      } catch (InterruptedException e) {
                          e.printStackTrace();
                      }
                      System.out.println("您购买的票已剩余"+ticket+ "张");
                  }
             }
    
    }

### <3>同步代码块 ###

package com.vince;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class ThreadDemo4 {
        public static void main(String[] args) {
           MyRunnable5 mr5 = new MyRunnable5();
           Thread t1 = new Thread(mr5);
           Thread t2 = new Thread(mr5);
           t1.start();
           t2.start();
        }
    }
    
    class MyRunnable5 implements Runnable{
        private int ticket = 10;//售票
           @Override
        public void run() {
           for(int i =0; i < 300; i++){
               synchronized (this){
                  if(ticket > 0){
                      ticket--;
                      try {
                          Thread.sleep(500);
                      } catch (InterruptedException e) {
                          e.printStackTrace();
                      }
                      System.out.println("您购买的票已剩余"+ticket+ "张");
                  }
               }
            }
        }
      
    }

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