在应该被通知之前通知线程，一种生产者消费者问题白板问题，找不到合适的算法JAVA

如何解决在应该被通知之前通知线程，一种生产者消费者问题白板问题，找不到合适的算法JAVA

所以，我正在尝试编写一个程序，其中老师有一块白板来写行，学生应该复制它。老师只允许在所有学生完成输入的行后在白板上写另一行（基本上老师一次只能写一行）。这是预期的输出：

显示器已交给白板...

class WhiteBoard{
    String text;
    int noOfStudents=0;
    boolean flag=true; //If teacher writes "end" on the white board the program terminates
    int c=0; //if c=0 teacher writes (Counter)
    Scanner sc=new Scanner(System.in);

    synchronized public void write(){ //Teacher uses this function
        while (c != 0) {
            try {
                wait();
            } catch (Exception e) {

            }
        }
        System.out.print("\nWrite on White Board: ");
        text=sc.nextLine();
        c=1; //To allow the students to copy the line
        if(text.equals("end")){
            flag=false;
        }
        notifyAll();

    }

    synchronized String read(String name){ //Student uses this fucntion
        while (c == 0) {
            try {
                wait();
            } catch (Exception e) {

            }
        }

        //I think the error is here:
        c++;
        c=(c%(noOfStudents+1)); //
        
        if(c==0){ //I know this is totally wrong but i cant find a way to put a successful lock
            notify();
        }
        

        return name+" Has finished copying: "+text;
    }

}

我得到的输出：

但是如果我在教师和学生类的 run() 方法中调用 sleep() 输出结果很好。 剩下的代码如下：

class Teacher extends Thread{

    WhiteBoard w;
    Teacher(WhiteBoard w){
        this.w=w;
    }


    public void run(){
        while(w.flag) {
            w.write();
            //If i write sleep here then i get the desired output only
            //try{Thread.sleep(100);}catch(Exception e){}
        }
    }

}

class Student extends Thread{
    WhiteBoard w;
    String name;
    Student(String name,WhiteBoard w){
        this.w=w;
        this.name=name;
        w.noOfStudents++;
    }

    public void run(){
        do{
            //If i write sleep here then i get the desired output only
            //try{Thread.sleep(100);}catch(Exception e){}
            System.out.println(w.read(name));
        }while(w.flag);
    }
}


public class Main {

    public static void main(String[] args) {
    // write your code here
        WhiteBoard wh=new WhiteBoard();
        Teacher t=new Teacher(wh);
        Student s1=new Student("Ram",wh);
        Student s2=new Student("Shyam",wh);
        Student s3=new Student("Hari",wh);
        t.start();
        s1.start();
        s2.start();
        s3.start();

    }
}

你能帮我找到同步写入和读取方法的算法吗？

解决方法

学生线程之间存在对白板访问权限的争用。线程调度器可以调度同一个线程依次从白板上读取，而不是按照您希望的方式轮流与其他学生线程。睡眠会导致每个学生线程暂停，让另一个学生线程从白板上读取。这允许每个线程从白板上读取老师写的每条消息。