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problem with threads :(

•

Join Date: Dec 2006

Posts: 43

Reputation: itchap is an unknown quantity at this point

Solved Threads: 0

itchap

Offline

Light Poster

problem with threads :(

Dec 22nd, 2006

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:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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.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;
  }
}

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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 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...");
   
  }
}

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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...");
  }
}
 
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...");
  }
}

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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();
}
}
 
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

•

Join Date: Nov 2004

Posts: 6,143

Reputation: jwenting is just really nice

Solved Threads: 213

jwenting

Offline

duckman

Re: problem with threads :(

Dec 22nd, 2006

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.

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.

•

Join Date: Dec 2006

Posts: 43

Reputation: itchap is an unknown quantity at this point

Solved Threads: 0

itchap

Offline

Light Poster

Re: problem with threads :(

Dec 22nd, 2006

Thanks jwenting

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

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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.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;
  }
}

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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 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...");
  }
}

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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...");
 
  }
}
 
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...");
   
  }
}

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
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();
  }
 }
 
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

•

Join Date: Nov 2004

Posts: 6,143

Reputation: jwenting is just really nice

Solved Threads: 213

jwenting

Offline

duckman

Re: problem with threads :(

Dec 22nd, 2006

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.

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.