Question

我不理解我的错误，我会描述它然后我会发布我的代码。从main（）我想运行3个线程（每个线程包含3个女性的循环）。我有一个方法打印每个进入浴室的女人和每个女人。我想使用锁定，所以每个线程中的每3个女人都会在下一个帖子发生之前写出。输出应该是这样的：女人0进入浴室女人0退出浴室女人1进入浴室女人1离开浴室女人2进入浴室女人2离开浴室然后每个线程2次。我的问题是，只有一个线程正在写入，2个没有到达锁定仍在等待我释放锁定后。这是我的代码:( BathRoom类）

private Lock lockW=new ReentrantLock();
public int women_present;


public BathRoom(){
    women_present=0;//empty at start
}



public  void woman_wants_to_enter (int i) {
     lockW.lock();

     women_present++;
     System.out.println ("Woman " + i + " enters bathroom ");     }
public  void woman_leaves (int i) {
   try {
        Thread.sleep (1000);

     }catch (InterruptedException e) {
         e.printStackTrace();
     }
   System.out.println ("Woman " + i + " exits bathroom ");
   if((women_present%3)==0){
       women_present=0;
       lockW.unlock();
   } }

这是女性班：

private int i; /* This identifies the woman. */
   private BathRoom bathroom;

public Woman (BathRoom bathroom,int i) { 
      this.i = i;
      this.bathroom = bathroom;
   }

public void run () {
 for (int i = 0; i < 3; i++) {
    try {
            Thread.sleep ((long) (500 * Math.random()));
         }catch (InterruptedException e) {
             e.printStackTrace();
         }
         bathroom.woman_wants_to_enter (i);
         bathroom.woman_leaves (i);
      }
   }}

Answer 1

我冒昧地修改你的代码：

  package stackoverflow;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class BathRoom {
    private Lock lockW=new ReentrantLock();
    private Condition c1=lockW.newCondition();
    public int women_present;


    public BathRoom(){
        women_present=0;//empty at start
    }



    public  void woman_wants_to_enter (int i) {
         lockW.lock();
         while(women_present!=i)
            try {
                c1.await();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }


         System.out.println ("Woman " + i + " enters bathroom ");     }
    public  void woman_leaves (int i) {
       try {
            Thread.sleep (1000);

         }catch (InterruptedException e) {
             e.printStackTrace();
         }
       System.out.println ("Woman " + i + " exits bathroom ");
       women_present++;    
       if(women_present==3){
           women_present=0;
        }
       c1.signal();
       lockW.unlock();
 }
}
class Woman implements Runnable{
    private int i; /* This identifies the woman. */
       private BathRoom bathroom;

    public Woman (BathRoom bathroom,int i) { 
          this.i = i;
          this.bathroom = bathroom;
       }

    public void run () {
     for (int i = 0; i < 3; i++) {
        try {
                Thread.sleep ((long) (500 * Math.random()));
             }catch (InterruptedException e) {
                 e.printStackTrace();
             }
             bathroom.woman_wants_to_enter (i);
             bathroom.woman_leaves (i);
          }
       }
    }

public class testdummy {

    public static void main(String[] args) {

        BathRoom b=new BathRoom();

        Woman w0=new Woman(b, 0);
        Woman w1=new Woman(b, 1);
        Woman w2=new Woman(b, 2);

        Thread A=new Thread(w0);
        Thread B=new Thread(w1);
        Thread C=new Thread(w2);

        A.start();
        B.start();
        C.start();



    }

}

我已经使用 Condition对象来同步线程访问方法 ，它不完美但它有效，希望它会给你一个更好的方法的想法

Answer 2

第一个帖子在woman_wants_to_enter（）中，线程获取lock（）继续。 woman_present设置为1。

在woman_leaves（）中，woman_present仍为1 if（1 mod 3为1）因此不会调用解锁

第二个线程进入woman_wants_to_enter（），但正在等待锁定

锁定3个线程

2 个答案: