problem with threads :(

[itchap]

Hi Everyone,

I'am currently working on this question:

Write a producer-consumer problem that uses threads and shares a common buffer. However do not use semaphores or any other synchronization primitives to guard the shared data structures. Just let each thread access them when it wants to. Use sleep and wakeup to handle the full and empty conditions. See how long it takes for a fatal race condition to occur. For example you might have the producer print a number once in a while. Do not print that number every minute because the I/O could affect the race conditions.

This is what I managed to do:

import java.nio.*;
 
public class Buffer {
  private int buffer = -1;
 
  public void set(int val)
  {
      System.out.println("Writing" + val);
      buffer = val;
  }
    
  public int get()
  {
      System.out.println("Reading" + buffer);
      return buffer;
  }
}

import java.lang.*;
import java.nio.*;

public class Consumer extends Thread implements Runnable{
 
 private Buffer sharedBuf; // the buffer is the same buffer used by the producer
 int sum = 0; // total stuff read from the buffer
 
 
//..constructor should accept(Buffer), and set it to the sharedBuf ...
 
 public Consumer (Buffer sharedBuf){
  this.sharedBuf=sharedBuf;
 }

  public void threadRun() throws InterruptedException {
   try{
      // read the buffer four times, and keep the total
      for (int i=1; i<=4; i++)
      {
         sleep(1);
         sum = sum + sharedBuf.get();
      }
}
   
   catch(InterruptedException exception) {
         exception.printStackTrace();
        }
      
     System.out.println("Consumer finished, ate " + sum + "exiting...");
   
  }
}

import java.lang.*;
import java.nio.*;

public class Producer extends Thread implements Runnable{
 
private Buffer sharedBuf; // the buffer is the buffer class above
// constructor should accept (Buffer), and set it to the sharedBuf ...
public Producer (Buffer sharedBuf){
 this.sharedBuf=sharedBuf;
}
  public void threadRun()throws InterruptedException
  {
   try{
     for (int i=1; i<=4; i++)
     {
        sleep(1);//sleep for a random time, between 0-3 seconds for example;
        sharedBuf.set(i);
     }
   }
     
     catch (InterruptedException exception) {
        exception.printStackTrace();
       }
    
        System.out.println("Producer finished, exiting...");
  }
}

public class test {
 public static void main(String args[]) { 
   Buffer shared = new Buffer();
   Thread a=new Thread( new Producer(shared));
   a.start();
   Thread b=new Thread( new Consumer(shared));
   b.start();
}
}

My problem is that I cant get my program to give me a output, and i dont know where im supposed to put my wakeup statements....

Thanks for your help in advance,

itchap

[jwenting]

Either extend Thread OR implement Runnable, no need to do both.
And the method you need is simply called "run()", not "threadRun()".
Your threads are running nicely, they're just not doing anything because the empty run() method in Thread (which you tried to override but didn't) doesn't do anything.

[itchap]

Thanks jwenting :D ....yeah your right, I fixed the code to this:

import java.nio.*;
public class Buffer {
  private int buffer = -1;
 
  public void set(int val)
  {
      System.out.println("Writing" + val);
      buffer = val;
  }
    
  public int get()
  {
      System.out.println("Reading" + buffer);
      return buffer;
  }
}

import java.lang.*;
import java.nio.*;

public class Producer implements Runnable{
 
private Buffer sharedBuf; // the buffer is the buffer class above
// constructor should accept (Buffer), and set it to the sharedBuf ...
public Producer (Buffer sharedBuf){
 this.sharedBuf=sharedBuf;
}
  public void run()
  {
   try{
     for (int i=1; i<=4; i++)
     {
      Thread.currentThread().sleep(3); //sleep for a random time, between 0-3 seconds for example;
        sharedBuf.set(i);
     }
   }
     
     catch (InterruptedException exception) {
        exception.printStackTrace();
       }
    
        System.out.println("Producer finished, exiting...");
  }
}

import java.lang.*;
import java.nio.*;

public class Consumer implements Runnable{
 
 private Buffer sharedBuf; // the buffer is the same buffer used by the producer
 int sum = 0; // total stuff read from the buffer
 
 
//..constructor should accept(Buffer), and set it to the sharedBuf ...
 
 public Consumer (Buffer sharedBuf){
  this.sharedBuf=sharedBuf;
 }

  public void run() {
   try{
      // read the buffer four times, and keep the total
      for (int i=1; i<=4; i++)
      {
       Thread.currentThread().sleep(3);
         sum = sum + sharedBuf.get();
      }
}
   
   catch(InterruptedException exception) {
         exception.printStackTrace();
        }
      
     System.out.println("Consumer finished, ate " + sum + "exiting...");
   
  }
}

public class test {
 public static void main(String args[]) { 
   Buffer shared = new Buffer();
   Thread t=new Thread( new Producer(shared));
   t.start();
   Thread b=new Thread( new Consumer(shared));
   b.start();
  }
 }

my threads are working properly, but, i dont think that they're doing what they are supposed to be, because the consumer is eating 10, and it shouldnt be......can you give me a clue to why it keeps doing that?

thanks once again

itchap

[jwenting]

what do you THINK it should do?

You have of course not created a consumer/producer system here at all.
You just have 2 threads where one sets a value and the other reads it from an object that's accessible to both.

If you get the same output each time that's possible but not certain at all.