Re: Java Thread Problem

From:
Lew <lew@lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Fri, 21 Mar 2008 07:43:06 -0400
Message-ID:
<gOydnbS2Hs3XAn7anZ2dnUVZ_gydnZ2d@comcast.com>
Sanny wrote:

I use a thread to call a function in a new thread.

Here is the code I use


But only fragments of it. You need to provide an SSCCE.
<http://mindprod.com/jgloss/sscce.html>

 private Thread runner2;

public void start2(){
  runner2 = new Thread(this);
  runner2.setPriority(Thread.MAX_PRIORITY);


Do not muck with Thread priorities here.

  runner2.start();
}

and in run of thread

 public void run(){

Thread thisThread = Thread.currentThread();


If you only use 'thisThread' once, for the comparison, you have no need for
the variable. Just use the currentThread() expression directly.

if (runner2==thisThread){


This check-and-set idiom will fail, absent some form of synchronization.

  runner2.setPriority(Thread.MAX_PRIORITY);


Do not set Thread priorities until you know more about how threads work.

callfunction1();


Since you're already seen to be calling a function, this isn't a great name
for a method. Also, use camel case in the name.

..

<http://mindprod.com/jgloss/sscce.html>

..

<http://mindprod.com/jgloss/sscce.html>

..
..

start2();to start a new thread


Is this supposed to be part of the code snippet, or part of the narrative?

// END THIS THREAD

 runner2=null;
  try{
  runner2.destroy();


Do you read the API docs? You should.
<http://java.sun.com/javase/6/docs/api/java/lang/Thread.html#destroy()>

**Deprecated.** ... the method was never implemented.
If if were to be implemented, it would be deadlock-prone


Whoops.

   }catch (NullPointerException e){
    //System.out.println("Bad URL: "+page);


As shown, the code is guaranteed to throw this exception. Well, nearly
guaranteed; concurrency anomalies might actually prevent the exception.

  }
  }

I use start2() to start a new runner2 thread.

But my Question is When I call the function to start a new thread Will
the Original thread runner2 stopped or a new thread runner2 will be
created?

I want that runner2 thread first stop and then start a new thread
runner2. How to destroy a thread and start it again.


Why would you want to destroy the thread? Why start it at all if you're
planning to destroy it? I don't understand.

Once I call runner2.destroy, will that thread stops? And in case I


What thread? You have runner2 set to null, unless a concurrent action somehow
breaks through the memory barrier and changes it.

Even if runner2 referenced a Thread, the destroy() wouldn't stop it, because
"the method was never implemented"!

start a new thread runner2 will the old thread destroy both old & new
threads as both use same variable runner2?


There is a difference between the variable and the object to which it points.
  Actions come from objects, not variables.

--
Lew

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