Re: Join thread with SwingWorker objects

Douwe <>
Fri, 27 Nov 2009 09:02:33 -0800 (PST)
Where should I start :/. First of all the field
SchedulerTask.activeProcesses is accessed from different Threads so
you should make it volatile. The next piece of code is causing your
processor (or at least 1 core of it) to go to 100 %

while (activeProcesses>0) {
            //do nothing...waiting...

you could insert a wait in there like

final Object lock = new Object(); // you can move this more to the
top of the class as a class field.
while (activeProcesses>0) {
  synchronized(lock) { try { lock.wait(100l); } catch(ignore)
{} } // puts the current thread into the wait state for 100 ms (you
could also do Thread.sleep instead) but I preffer the Object.wait()

Next is the main loop

 while (lastIndex<items.size()) {
            while(lastIndex<items.size() &&
activeProcesses<MAX_ACTIVE_PROCESSES) {

            for (BatchExtractionItem item: currentProcesses) {
                if (!item.getStatus().equals
(BatchExtractionItem.COMPLETED) && !item.getStatus().equals
(BatchExtractionItem.PROCESSING)) {
                    BatchTask task = new BatchTask(item);

This part is split in two subparts: the first part adds items to the
currentProcesses as long as the activeProcesses is under a certain
amount. The second part then runs through the list of currentProcesses
and starts BatchTasks for items that have not started yet. Now imagine
what happens when activeProcesses is exactly MAX_ACTIVE_PROCESSES then
the first part will not enter the loop and the second part will enter
the loop but see that all processes are running and thus does nothing
more then checks. These two parts than get repeated over and over and
over until one of the BatchTasks finishes. This loop will therefor
also cause the CPU (or 1 core) to got to 100%. Try implementing
something like the following piece of code

private final Object lock = new Object();
private volatile int countCompleted;
pricate volatile int activeProcesses;

public void processCompleted(BatchExtractionItem completedItem) {
        //System.out.println("Completed "+completedItem);

    synchronized(lock) {
  lock.notifyAll(); // wake up the main thread

enum State { WAITING, RUN_NEXT };

protected Integer doInBackground() throws Exception {

    List<BatchExtractionItem> queuedItems = new
        activeProcesses = 0;
        countCompleted = 0;
        boolean keepRunning = true;
        BatchExtractionItem itemToRun = null;

    while (keep_running) {
        switch(state) {
            case WAITING : {
                      synchronized(lock) {
                      if (activeProcesses<MAX_ACTIVE_PROCESSES) {
                      if (queuedItems.isEmpty()) {
                      if (activeProcesses==0) {
                      keep_running = false;
                      } else {
                          state = FIND_TO_RUN;
                      try {
                          lock.wait(20000l); // wait for 20 seconds max
(or a notify from processCompleted) and then check again
                          } catch(Exception ignore) {}
                     } break;

             case RUN_NEXT : {
              BatchExtractionItem item = queuedItems.removeLast(queuedItems);
                if (!item.getStatus().equals(BatchExtractionItem.COMPLETED) && !
item.getStatus().equals(BatchExtractionItem.PROCESSING)) {
                    BatchTask task = new BatchTask(item);
                } else {
                    // spitt out a warning
                    System.err.println("warn: next item was already processing or has
                    // countCompleted++; // add this if it should be counted as a
completed task
                state = WAITING;
            } break;
    // no further checking needed ... all items have finised processing
    return 0;

public void actionPerformed(ActionEvent e) {
    //issued by Timer event
    int progress = countCompleted/items.size();

Please note that I didn't test the code and I have edited the code
without an Java compatible IDE so you might need some small

Douwe Vos

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