wiki-export/wiki-content/DevFaqRequestProcessorTask.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!--
    Licensed to the Apache Software Foundation (ASF) under one
    or more contributor license agreements.  See the NOTICE file
    distributed with this work for additional information
    regarding copyright ownership.  The ASF licenses this file
    to you under the Apache License, Version 2.0 (the
    "License"); you may not use this file except in compliance
    with the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing,
    software distributed under the License is distributed on an
    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    KIND, either express or implied.  See the License for the
    specific language governing permissions and limitations
    under the License.

--><mediawiki xmlns="http://www.mediawiki.org/xml/export-0.3/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="0.3" xml:lang="en" xsi:schemaLocation="http://www.mediawiki.org/xml/export-0.3/ http://www.mediawiki.org/xml/export-0.3.xsd">
  <siteinfo>
    <sitename>NetBeans Wiki</sitename>
    <base>http://wiki.netbeans.org/Main_Page</base>
    <generator>MediaWiki 1.15.1</generator>
    <case>first-letter</case>
    <namespaces>
      <namespace key="-2">Media</namespace>
      <namespace key="-1">Special</namespace>
      <namespace key="0"/>
      <namespace key="1">Talk</namespace>
      <namespace key="2">User</namespace>
      <namespace key="3">User talk</namespace>
      <namespace key="4">NetBeans Wiki</namespace>
      <namespace key="5">NetBeans Wiki talk</namespace>
      <namespace key="6">File</namespace>
      <namespace key="7">File talk</namespace>
      <namespace key="8">MediaWiki</namespace>
      <namespace key="9">MediaWiki talk</namespace>
      <namespace key="10">Template</namespace>
      <namespace key="11">Template talk</namespace>
      <namespace key="12">Help</namespace>
      <namespace key="13">Help talk</namespace>
      <namespace key="14">Category</namespace>
      <namespace key="15">Category talk</namespace>
    </namespaces>
  </siteinfo>
  <page>
    <title>DevFaqRequestProcessorTask</title>
    <id>7452</id>
    <revision>
      <id>26236</id>
      <timestamp>2009-11-06T15:59:19Z</timestamp>
      <contributor>
        <username>Admin</username>
        <id>1</id>
      </contributor>
      <text xml:space="preserve">__NOTOC__
===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 &lt;tt&gt;task.schedule(3000)&lt;/tt&gt; 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 [[DevFaqRequestProcessor| 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.  &lt;tt&gt;RequestProcessor.Task&lt;/tt&gt; makes this sort of thing easy.

&lt;pre&gt;
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()) &amp;&amp; !obj.isModified()) { //file was saved
      task.schedule(100);
    }
  }

  @Override
  public String getHtmlDisplayName() {
    return error ? "&lt;font color=\"!nb.errorForeground\"&gt;" + 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
  }
}
&lt;/pre&gt;</text>
    </revision>
  </page>
</mediawiki>