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Java thread question-- How to check if threads are dead in a threadGroup

Posted on 2006-06-09
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Last Modified: 2008-02-26
below is a bare bones threaded app. my questions are in the comments. Thanks in advance for your help.
-jbd


import java.util.*;

public class tester {
   
     public static void main (String[] args) {
        new tester().tester1();
     }  
       
       public void tester1 () {
            try{
                new ReadThread();
                new ReadThread();
               
                //----1-----
                //How can I check to make sure that the threads have finished processing.
                //I think I need to use activeCount() for the thread group
                //but I can't seem to figure out how to associate these threads with a threadgroup
                //though, by default they are in main, and I can't seem to get an active count for threadgroup main
               
           } catch (Exception ex) {
                   System.out.println(ex);
                   ex.printStackTrace();
           }
       }
       
       static class ReadThread extends Thread {
           public int thisThreadNum;
                     
           ReadThread(){
                start();
            }

            public void run() {
                //----2-----
                 //There's a bunch of code here. How do I make sure the thread dies after this code executes.
                //the docs say I need to return something to the run method? not exactly sure how to make sense of that
           
            }
       }
}
0
Comment
Question by:jacobbdrew
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8 Comments
 
LVL 26

Expert Comment

by:ksivananth
ID: 16874265
thread.isAlive() going to tell u whether the thread is dead or not
0
 
LVL 26

Expert Comment

by:ksivananth
ID: 16874298
hey u need not return anything from run method. unless there is a condition or another thread launched, all the code inside run method will get executed before the thread dies.
0
 
LVL 26

Expert Comment

by:ksivananth
ID: 16874304
>>//How can I check to make sure that the threads have finished processing.

you can use join method for this.
0
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LVL 26

Expert Comment

by:ksivananth
ID: 16874311
unless there is a need for grouping thread, no need to go for it and in your case it seems not needed.
0
 
LVL 1

Author Comment

by:jacobbdrew
ID: 16874380
OK. Can you show me how I would implement Thread.isAlive(). bascailly, i need something like this, but that works:
...
 public void tester1 () {
            try{
                new ReadThread(); //where this is thread1
                new ReadThread(); //and this is thread2
               
             //can't get the isAlive part to work here....
              if( !Thread1.isAlive() && !Thread2.isAlive() ){
                          //now tell the database the processing is finished (this part i can do)
             }
               
           } catch (Exception ex) {
                   System.out.println(ex);
                   ex.printStackTrace();
           }
       }
0
 
LVL 26

Accepted Solution

by:
ksivananth earned 500 total points
ID: 16874394
try this,

public void tester1 () {
            try{
                Thread thread1 = new ReadThread(); //where this is thread1
                Thread thread2 = new ReadThread(); //and this is thread2

thread1.join() ;
thread2.join() ;
               
             //can't get the isAlive part to work here....
//              if( !Thread1.isAlive() && !Thread2.isAlive() ){
                          //now tell the database the processing is finished (this part i can do)
//             }
               
           } catch (Exception ex) {
                   System.out.println(ex);
                   ex.printStackTrace();
           }
       }
0
 
LVL 16

Expert Comment

by:imladris
ID: 16874399
The best way to do that is to keep a reference to the threads, and then call join on them:

 public void tester1 () {

            Thread t1,t2;

            try{
                t1=new ReadThread(); //where this is thread1
                t2=new ReadThread(); //and this is thread2
               
                t1.join();
                t2.join();
                          //now tell the database the processing is finished (this part i can do)
               
           } catch (Exception ex) {
                   System.out.println(ex);
                   ex.printStackTrace();
           }
       }

The join method waits for the thread to "join" this one (by finishing its processing).
0
 
LVL 92

Expert Comment

by:objects
ID: 16874419
In java 5 you can use the threads getState() method to determine if it has terminated

http://java.sun.com/docs/books/tutorial/essential/threads/lifecycle.html

problem with isAlive() is that it also returns true before the thread has started.
To use join() code would look like:

public void tester1 () {
            try{
                Thread t1 = new ReadThread(); //where this is thread1
                Thread t2 = new ReadThread(); //and this is thread2
                t1.join();
                t2.join();

               //now tell the database the processing is finished (this part i can do)
               
           } catch (Exception ex) {
                   System.out.println(ex);
                   ex.printStackTrace();
           }
       }

another option would be to have the thred iitself tell the database processing has finished
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