Question

wais for multiple objects

Asked by: sey7

Hello,
     
   I want to make a small program with two threads:
- one that add some numbers
- one that multiplies some numbers
In main I start both threads. How can I know when both threads are finished? (using notify and wait).


Thank You,
     sey.

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Asked On
2002-01-09 at 04:57:20ID20253093
Topic

Java Programming Language

Participating Experts
3
Points
200
Comments
6

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Answers

 

by: antonsPosted on 2002-01-09 at 06:17:47ID: 6720608

there is a lot of possibilities ...
for example lets the clas with the main method is named AA
then the main method after starting the both threads
executes the
synchronized(AA.class) {
     AA.class.wait();
}


and AA implements the method
private static int numberOfFinished = 0;
public static synchronized wakeUp() {
     numberOfFinished++;
     if(numberOfFinished>1) AA.class.notify();    
}

your working threads will call wakeUp() when they finish the work.

 

by: heyhey_Posted on 2002-01-10 at 02:19:05ID: 6723139

the best solution is

thread1.join();
thread2.join();

 

by: mariusoPosted on 2002-01-10 at 06:02:15ID: 6723605

Or package tst;

public class produs extends Thread {
     
    private Object monitor;
    int max;
    int p = 1;
     
    public produs(int i, Object m){
        max = i;
        monitor = m;
    }

    public void run(){
        for(int i = 1; i < max; i++){
            p *= i;
            System.out.println("i = " + i);
        }
        synchronized (monitor){
            monitor.notify();
            System.out.println("Produs = " + p);
            done = true;
        }
    }


    private boolean done = false;
     
    public boolean finished() {
        return done;
    }


}
 




package tst;
 
public class suma extends Thread {
    private Object monitor;
    int max;
    int s = 0;
     
    public suma(int i, Object m){
        max = i;
        monitor = m;
    }
     
    public void run(){
        for(int i = 0; i < max; i++){
            s += i;
        }
        synchronized (monitor){
            monitor.notify();
            System.out.println("Suma = " + s);
            done = true;
        }
    }
    private boolean done = false;

    public boolean finished() {
        return done;
    }
     
}


package tst;

public class Test
{
     public static void main(String [] args){
          Object m = new Object();
          Object m1 = new Object();
          suma s = new suma(100, m);
          produs p = new produs(100, m1);
          p.start();
          s.start();
          try{
               synchronized (m){
                            if (!p.finished())
                    m.wait();
               }
               synchronized(m1){
                            if (!s.finished())
                    m1.wait();
               }
          }catch(InterruptedException e){
                    e.printStackTrace();
                }
          System.out.println("Total = " + (s.s + p.p));
     }
}




Using join for such simple example is possible too but how to sinc many threads in many points (usual case of randevous). For this u can use Real Time Java API provided by many vendors.
 

 

by: mariusoPosted on 2002-01-17 at 23:44:41ID: 6741132

Points ?

 

by: heyhey_Posted on 2002-01-23 at 01:36:44ID: 6750582

mariuso
your code is SIMPLY WRONG.

there is a classic race condition in this part of the code  (you can ask any expert)

synchronized (m){
  if (!p.finished())
  m.wait();
}

 

by: heyhey_Posted on 2002-01-23 at 05:30:45ID: 6750915

well it's up to you.

WRONG CODE is WRONG CODE. if you use it ... well - good luck ...

I'm off.

20120131-EE-VQP-002

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