线程同步机制(Synchronized)

线程同步 synchronized

多线程操作统一资源(临界资源)时,需要同步机制;


队列和锁

  1. 不安全买票
public class UnsafeBuyTicket {
	public static void main (String[] args) {
		BuyTicket station =new BuyTicket();
		new Thread(station,"我").start();
		new Thread(station,"你").start();
		new Thread(station,"该死的黄牛").start();
		
	}

}
class BuyTicket implements Runnable{

	private int ticketNums=10;
	boolean flag= true;
	
	@Override
	public void run() {
		// 买票
		while(flag) {
			try {
				buy();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
	
	private void buy() throws InterruptedException {
		//判断是否有票
		if(ticketNums<=0) {
			flag=false;
			return;
		}
		
		//模拟延时
		Thread.sleep(100);
		//买票
		System.out.println(Thread.currentThread().getName()+"拿到了"+ticketNums--);
	}
	
}
  1. 不安全的取钱(银行)

    package synchronize;
    
    
    //两个人去银行取钱,账户
    public class UnsafeBank {
    	public static void main(String[] args) {
    		Account account=new Account(100,"结婚基金");
    		Drawing you =new Drawing(account,50,"你");
    		Drawing girlfriend =new Drawing(account,100,"girlfriend");
    		
    		you.start();
    		girlfriend.start();
    	}
    }
    
    //账户
    class Account{
    	int money;//余额
    	String name;//卡名
    	 public Account (int money, String name) {
    		 this.money=money;
    		 this.name=name;
    	 }
    
    }
    
    
    //银行模拟取款
    class Drawing extends Thread{
    	Account account;//账户
    	int drawingMoney;//取多少钱
    	int nowMoney;//手中有多少钱
    	
    	public Drawing(Account account,int drawingMoney,String name) {//有参构造器
    		super(name);//给线程名字
    		this.account=account;
    		this.drawingMoney=drawingMoney;
    		
    	}
    	
    	
    	//取钱方法
    	public void run() {
    		//先判断有没有钱
    		if (account.money-drawingMoney<0) {
    			System.out.println(Thread.currentThread().getName()+"钱不够,取不出来!");
    			return;
    		}
    		
    		try {//增加延时,放大问题发生性
    			Thread.sleep(1000);
    		} catch (InterruptedException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		//卡内余额=余额-取出的钱;
    		account.money-=drawingMoney;
    		//手里的钱
    		nowMoney += drawingMoney;
    		
    		System.out.println(account.name+"余额为:"+account.money);
    		System.out.println(this.getName()+"手里的钱为:"+nowMoney);
    		
    	}
    }
    
  2. 线程不完全的集合

    import java.util.List;
    import java.util.ArrayList;
    //线程不安全的集合
    public class MyTest {
        public static void main(String[] args) throws InterruptedException {
            List<String> list = new ArrayList<>();
            for (int i = 0; i < 10000; i++) {
                new Thread(()->{
                    list.add(Thread.currentThread().getName()
                    );
                }).start();
            }
            Thread.sleep(2000);
            System.out.println(list.size());
        }
    }
    
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