執行緒同步

1. 多個執行緒訪問同一個物件叫併發。

2. 執行緒同步就是：排隊

3. 佇列和 鎖 解決執行緒的安全性問題

4. synchronized,當一個執行緒獲得物件的排它鎖，獨佔資源,其他執行緒必須等待，使用夠釋放鎖即可。

5. 程式碼塊鎖可以鎖任何地方。

   package Thread;
   ​
   public class UnsafyBuyTickets {
      public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
        new Thread(buyTicket,"明").start();
        new Thread(buyTicket,"剛").start();
        new Thread(buyTicket,"老闆").start();
   ​
      }
   }
   class BuyTicket implements Runnable{
      private int tickets = 10;
      boolean falg = true;
      @Override
      public void run() {
     //買票
        while(falg){
          buy();
        }
   ​
      }
      private synchronized void buy(){
        //判斷是否有票
        if (tickets<=0){
          falg = false;
          return;
        }
        //模擬程式碼延時
        try {
          Thread.sleep(100);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()+"拿到"+tickets--+"張票");
      }
   }
    
   

   package Thread;
   ​
   public class UnsafyBank {
      public static void main(String[] args) {
        Account account = new Account(2000000,"彩禮");
        Drawing you = new Drawing(account,1000000,"自己");
        Drawing wife = new Drawing(account,2000000,"妻子");
        you.start();
        wife.start();
      }
   }
   class Account {
     int money;
     String name;
     public Account(int money,String name){
       this.money = money;
       this.name = name;
     }
   }
   //模擬：銀行取款
   class Drawing extends Thread{
      Account account;//賬戶
      int drawingMoney;//取了多少錢
      String name;
      //現在手裡有多少錢
      int nowMoney;
      public Drawing(Account account,int drawingMoney,String name){
        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;
   ​
        this.nowMoney = nowMoney;
      }
   ​
      @Override
      public  void run() {
        //鎖的對物件是變化的量，需要增刪改操作的量。
        synchronized (account){
        if(account.money-drawingMoney<0){
          System.out.println(Thread.currentThread().getName()+"錢不夠，取不了");
        return;
        }
   ​
        //模擬延時
        try {
          Thread.sleep(100);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        account.money = account.money-drawingMoney;
        nowMoney = nowMoney+drawingMoney;
        System.out.println(account.name+"餘額為"+account.money);
        System.out.println(this.getName()+"手裡的錢："+nowMoney);
      }
      }
   }
    
   

   package Thread;
   ​
   import java.util.ArrayList;
   import java.util.List;
   ​
   public class UnSafyList {
      public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
   ​
          for (int i = 0; i < 10000; i++) {
   ​
            new Thread(() -> {
              synchronized (list) {
              list.add(Thread.currentThread().getName());
              }
            }).start();
   ​
          }
        try {
          Thread.sleep(3000);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        System.out.println(list.size());
        }
   ​
   }
   ​