Thread cannot access the class variables.

Question

Hi
I have below code snippet : (Only section of which I have copied below)
public class ProcessAppendAction extends HttpServlet implements Runnable{
     public ProcessAppendAction ()
MI_OS_APPEND port ;
protected void doGet(
          HttpServletRequest request,
          HttpServletResponse response)
          throws ServletException, IOException {
          //TODO : Implement
port =
                    (MI_OS_APPEND) obj.getLogicalPort(
                         "MI_OS_APPENDPort",
                         MI_OS_APPEND.class);
Thread[] threads = new Thread[noOfThreads];
ProcessAppendAction run = new ProcessAppendAction(req);
                                        Thread th = new Thread(run);
                                        threads[no] = th;          
                              threads[no].start();
                              threads[no].join();
public ProcessAppendAction(DT_REQUEST_APPEND req) {
          this.requestObj = req;
          // TODO Auto-generated constructor stub
public void run()
          try
               DT_RESPONSE res = this.port.MI_OS_APPEND(requestObj);
                              catch(Exception e)
                                   int ch=0;
                                   ch++;
          }     In above code I am successfully creating an object in line :
port =
                    (MI_OS_APPEND) obj.getLogicalPort(
                         "MI_OS_APPENDPort",
                         MI_OS_APPEND.class);But when I am trying to access this port variable in run method it is giving null.
Port in my code is a class variable.
Is it the case that thread cannot access class variable !!

Answer 1

money321 wrote:
ok, I have removed join() from just after start().So that now the Servlet can return before the new Thread has finished. Is this what you want?
First I did invoked all threads and then in second loop i invoked Join on all threads.I don't understand. Why do you need to join() all the threads since you only start one thread in this request. What am I missing?
>
Now, my problem.
It was solved when I substituted the line
ProcessAppendAction run = new ProcessAppendAction(req)
with
ProcessAppendAction run = new ProcessAppendAction(req,port);Of course. Instance variables in Servlet instances are a no-no so passing the 'port' though an instance variable is just wrong.
>
That is passes port alongwith req while creating thread object.
But still if class variables are not thread safe, then it means if I pass object 1 to thread 1.
And then try to pass object 2 to thread 2, it might be possibility that object 1 of thread 1 might be replaced by object 2.
So, thread 1 will get an updated value object 2.Yep - that is why you should not use instance variables in Servlets and why they are not thread safe.
>
Which is not what I intend to do...:-)