Waiting unknown threads to be completed.

Question

Hi all,
Here is my issue:
TaskRunner runner = TaskRunner.getInstance();
for(Task task : tasks) {
        runner.run(task);
System.out.println("Done!");Each task may (probably will) create one or more sub-threads... How can I ensure that, by the time I print "Done!", that every task has been completely executed?
Is there any way to wait for unknown threads to finish before continuing? By unknown, I mean I know absolutely nothing about them (no name, no group...).
EDIT - I must add I can't touch TaskRunner's code...
Thank you all in advance!
Best regards,
Guilherme
Edited by: guilherme.tramontina on Aug 16, 2009 8:28 AM
Edited by: guilherme.tramontina on Aug 16, 2009 8:43 AM

Answer 1

All,
ExecutorService didn't work for this specific issue.
So I solved my problem by doing the following:
Moved the "for" statement into a new Thread class. Please note the "super()" call... This new Thread is created into a new ThreadGroup.
public class TaskRunnerThread extends Thread {
     private List<Task> tasks;
     public TaskRunnerThread(List<Task> tasks) {
          super(new ThreadGroup("TRThreadGroup", "TRThread");
          this.tasks = tasks;
     public void run() {
          TaskRunner runner = TaskRunner.getInstance();
          for (Task task : tasks) {
               runner.run(task);
}And then...
TaskRunnerThread trThread = new TaskRunnerTask(tasks);
trThread.start();
groupJoin(tsThread.getThreadGroup());
System.out.println("Done!");Here is the "groupJoin" method:
private void join(ThreadGroup t) {
     synchronized (t) {
          while (t.activeCount() > 0) {
               try {
                    t.wait();
               } catch (InterruptedException e) {
                    e.printStackTrace();
}It worked like a charm!
Thanks for your help!
Best regards,
Guilherme