多執行緒

死鎖

• 多個執行緒互相持有對方需要的資源，然後形成僵持

public class DeadLock {
    public static void main(String[] args) {
        Makeup makeup = new Makeup(0,"莉莉");
        Makeup makeup1 = new Makeup(1,"紅紅");
        makeup.start();
        makeup1.start();
    }

}
class Lipstick{//口紅
}
class Mirror{//鏡子
}
class Makeup extends Thread{
    //需要的資源只有一份，用static保證
    static Lipstick l = new Lipstick();
    static Mirror m = new Mirror();
    int choice;
    String girlNmae;
    public Makeup(int choice,String girlNmae){
        this.choice=choice;
        this.girlNmae=girlNmae;
    }
    @Override
    public void run() {
        makeUp();
    }
    private void makeUp(){
        //化妝：互相持有對方的鎖，即需要拿到對方的資源
        if (choice==0){
            synchronized (l){//獲得口紅的鎖
                System.out.println(this.girlNmae+"獲得口紅的鎖");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            }
            //一個物件先將拿到的鎖釋放再拿別的物件的鎖，就不會出現死鎖
            synchronized (m){//一秒後再獲得鏡子的鎖
                System.out.println(this.girlNmae+"獲得鏡子的鎖");
            }
        }else{
            synchronized (m){//獲得鏡子的鎖
                System.out.println(this.girlNmae+"獲得鏡子的鎖");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            //一個物件先將拿到的鎖釋放再拿別的物件的鎖，就不會出現死鎖
            }
            synchronized (l){//一秒後獲得口紅的鎖
                System.out.println(this.girlNmae+"獲得口紅的鎖");
            }
        }
    }
}
 

Lock

• 更強大的執行緒同步機制——通過顯示定義同步鎖隨想來實現同步。用Lock物件