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HashMap re-set question.

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Join Date: May 2007

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Ezzaral

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Re: HashMap re-set question.

#11

Oct 13th, 2008

I should actually qualify this part a little bit:

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Originally Posted by Ezzaral

Additionally, if you are running on a single processor, starting 10 threads won't make it go faster - it will just have to time-slice the processing of each thread anyway.

If the process is CPU-bound, such as performing a lot of computations or loops, adding additional threads won't offer any improvement and may even make it slower due to the additional overhead of managing the threads themselves (synchronization, context switching, etc.). If the process performs some tasks that are constrained waiting on other resources like IO, multiple threads may offer improved performance even on single processor machines.

This article on thread pools and work queues covers some of these issues:
http://www.ibm.com/developerworks/li...j-jtp0730.html

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Re: HashMap re-set question.

#12

Oct 13th, 2008

Ezzaral,

The program is actually IO intensive. I am trying to write a migration program, which will read each content/metadata from a source repository and create its corresponding object (contetnt/metadata) to a target repository.

So, the program will be IO intensive as apposed to CPU, I believe.

So, will multi-thread help me in this senario?

Thanks for the suggestions.

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Ezzaral

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Re: HashMap re-set question.

#13

Oct 13th, 2008

Perhaps, but again it all depends on the processes, the hardware, how you divide and synchronize the work, etc. There isn't a single global answer there.

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Re: HashMap re-set question.

#14

Oct 13th, 2008

I agree with what you said.

Can you take a look at the following and see if its better now?

 Help with Code Tags 
 java Syntax (Toggle Plain Text) 
public class MigrationUtility {
    private HashMap map = new HashMap ();
 
    public static void main(String[] args){
        MigrationUtility m = new MigrationUtility ();
        m.loadMap();
 
        for (int j=0; j < 10; j++) {
            new Thread(new MigrationUtilityThread(m.map)).start();
        }
    }
 
    private void loadMap () {
	// This will be populated properly.
	// For now its dummy values for test only.
        for (int i = 0;i < 50; i++) {
            map.put(new Integer(i), new String("Some Value" + i));
        }
    }
}
 
class MigrationUtilityThread extends Thread{
    private HashMap m = null;
    MigrationUtilityThread(HashMap map){
        m = map;
    }
 
    public void run(){
        for (int j=0; j < m.size(); j++) {
            if (!m.get(new Integer(j)).toString().equalsIgnoreCase("Processed")) {
                m.put(new Integer(j), new String("Processed"));
                processItem(this.getName());                
            }
        }
    }
 
    public synchronized void processItem(String name) {
	// process items here...
        System.out.println("Item processed with thread: "+ name );
    }
}
public class MigrationUtility {
    private HashMap map = new HashMap ();
    
    public static void main(String[] args){
        MigrationUtility m = new MigrationUtility ();
        m.loadMap();
        
        for (int j=0; j < 10; j++) {
            new Thread(new MigrationUtilityThread(m.map)).start();
        }
    }
    
    private void loadMap () {
	// This will be populated properly.
	// For now its dummy values for test only.
        for (int i = 0;i < 50; i++) {
            map.put(new Integer(i), new String("Some Value" + i));
        }
    }
}

class MigrationUtilityThread extends Thread{
    private HashMap m = null;
    MigrationUtilityThread(HashMap map){
        m = map;
    }
    
    public void run(){
        for (int j=0; j < m.size(); j++) {
            if (!m.get(new Integer(j)).toString().equalsIgnoreCase("Processed")) {
                m.put(new Integer(j), new String("Processed"));
                processItem(this.getName());                
            }
        }
    }
    
    public synchronized void processItem(String name) {
	// process items here...
        System.out.println("Item processed with thread: "+ name );
    }
}

And this is the output of the program:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-16
Item processed with thread: Thread-4
Item processed with thread: Thread-6
Item processed with thread: Thread-8
Item processed with thread: Thread-2
Item processed with thread: Thread-12
Item processed with thread: Thread-18
Item processed with thread: Thread-10
Item processed with thread: Thread-14
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-0
Item processed with thread: Thread-16
Item processed with thread: Thread-4
Item processed with thread: Thread-6
Item processed with thread: Thread-8
Item processed with thread: Thread-2
Item processed with thread: Thread-12
Item processed with thread: Thread-18
Item processed with thread: Thread-10
Item processed with thread: Thread-14