netbeans.apache.org/src/content/wiki/DevFaqRequestProcessorTask.asciidoc

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= DevFaqRequestProcessorTask
:jbake-type: wiki
:jbake-tags: wiki, devfaq, needsreview
:jbake-status: published
:keywords: Apache NetBeans wiki DevFaqRequestProcessorTask
:description: Apache NetBeans wiki DevFaqRequestProcessorTask
:toc: left
:toc-title:
:syntax: true

=== How can I operation occasionally on a background thread, but reschedule it if something happens to delay it?

There are a lot of reasons you might want to reschedule a background operation.  For example, you want to re-parse a file 3 seconds after the user stops typing, so you can show errors.  But at 2 seconds she starts typing again.  You don't want that task to run a second from now anymore.  You can either cancel the task, or even simpler, call `task.schedule(3000)` every time a key is pressed.  If it was already scheduled, it will be rescheduled for 3 seconds from now again.

Or imagine you have the situation described in link:DevFaqRequestProcessor.asciidoc[the FAQ about RequestProcessor.getDefault()] - a node for a file needs to read the file after it is created to mark itself if the file has errors.  `RequestProcessor.Task` makes this sort of thing easy.

[source,java]
----

public class FooDataNode extends DataNode implements PropertyChangeListener, Runnable {
  private boolean error;
  private static final RequestProcessor THREAD_POOL = new RequestProcessor("FooDataNode processor", 1);
  private final RequestProcessor.Task task = THREAD_POOL.create(this);

  FooDataNode(FooDataObject obj) {
    super(obj, Children.LEAF);
    obj.addPropertyChangeListener(WeakListeners.propertyChange(this, obj));
    task.schedule(100);
  }

  public void propertyChange(PropertyChangeEvent evt) {
    DataObject obj = (DataObject) evt.getSource();
    if (DataObject.PROP_MODIFIED.equals(evt.getPropertyName()) && !obj.isModified()) { //file was saved
      task.schedule(100);
    }
  }

  @Override
  public String getHtmlDisplayName() {
    return error ? "<font color=\"!nb.errorForeground\">" + getDisplayName() : null;
  }

  public void run() {
    boolean old = error;
    error = doesTheFileHaveErrors();
    if (old != error) {
      fireDisplayNameChange(null, null);
    }
  }

  private boolean doesTheFileHaveErrors() {
    assert !EventQueue.isDispatchThread();
    //parse the file here
    return true; //whatever the value should be
  }
}
----

=== Apache Migration Information

The content in this page was kindly donated by Oracle Corp. to the
Apache Software Foundation.

This page was exported from link:http://wiki.netbeans.org/DevFaqRequestProcessorTask[http://wiki.netbeans.org/DevFaqRequestProcessorTask] , 
that was last modified by NetBeans user Admin 
on 2009-11-06T15:59:19Z.


*NOTE:* This document was automatically converted to the AsciiDoc format on 2018-02-07, and needs to be reviewed.