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From "Roger L. Whitcomb" <Roger.Whitc...@actian.com>
Subject RE: 2.0.1 release and threads
Date Mon, 16 Jan 2012 18:39:29 GMT
Hi Lukas,
	That approach is still valid (and encouraged) EXCEPT that all updates to the UI MUST happen
in the Event Dispatch Thread (or 'EDT').  This is now enforced in 2.0.1 (as you can see).
 This is inherent, not only in Pivot, but all other GUI frameworks (that I know of).  So,
even though it "appeared" to work fine with 2.0, there are/were subtle problems that you just
didn't see yet.
	What you need to do is use either a TaskAdapter class or call the ApplicationContext.queueCallback()
method to schedule your UI updates in the EDT, rather than doing them directly in the background
thread.  For an example you can look at the Tutorial here: http://pivot.apache.org/tutorials/background-tasks.html.
 I can step you through your code in more detail if you need more help.  Our application also
has a number of places where we have needed to do this.
	I'm going to transfer this to the User list since this is not a developer issue, per se,
since it is not a bug.  It is, however, something that has definitely changed (for the better)
in 2.0.1.
	Thank you for using Pivot, though!!

~Roger

-----Original Message-----
From: Lukáš Macháček [mailto:cgrim@coolmail.cz] 
Sent: Monday, January 16, 2012 8:17 AM
To: dev@pivot.apache.org
Subject: 2.0.1 release and threads

Hi all,

I am now testing coming 2.0.1 release of Pivot libraries with my desktop 
application developed during previous year on Pivot 2.0 and am facing 
one great problem with threads :-(

Every task which loads data at background and worked in 2.0 well now 
throws exception like this:

java.lang.IllegalStateException: this method can only be called from the 
AWT event dispatch thread, and not from "Thread-26"
     at org.apache.pivot.wtk.Container$1.check(Container.java:872)
     at 
org.apache.pivot.wtk.Container.assertEventDispatchThread(Container.java:880)
     at org.apache.pivot.wtk.Component.repaint(Component.java:2047)
     at org.apache.pivot.wtk.Component.repaint(Component.java:1998)
     at 
org.apache.pivot.wtk.skin.ComponentSkin.repaintComponent(ComponentSkin.java:351)
     at 
org.apache.pivot.wtk.skin.ComponentSkin.repaintComponent(ComponentSkin.java:346)
     at 
org.apache.pivot.wtk.skin.terra.TerraTableViewSkin.enabledChanged(TerraTableViewSkin.java:1394)
     at 
org.apache.pivot.wtk.Component$ComponentStateListenerList.enabledChanged(Component.java:399)
     at org.apache.pivot.wtk.Component.setEnabled(Component.java:2173)
     at cz.cgrim.alchemist.dql.RunQueryTask.execute(RunQueryTask.java:58)
     at cz.cgrim.alchemist.dql.RunQueryTask.execute(RunQueryTask.java:23)
     at 
org.apache.pivot.util.concurrent.Task$ExecuteCallback.run(Task.java:42)
     at 
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
     at java.util.concurrent.FutureTask.run(FutureTask.java:166)
     at java.lang.Thread.run(Thread.java:722)

In this example at first it disables TableView (to disable user 
interaction during background load of data), than it loaded results from 
DQL query into that TableView and at the end it enabled that TableView.

I have tens of use cases with similar approach in my application used to 
load data at background because it can take long time to finish while 
user can work on another tasks.

Another equal problem with thread has occurred for example in my custom 
Log4J Appender:

Exception in thread "Timer-2" java.lang.IllegalStateException: this 
method can only be called from the AWT event dispatch thread, and not 
from "Timer-2"
     at org.apache.pivot.wtk.Container$1.check(Container.java:872)
     at 
org.apache.pivot.wtk.Container.assertEventDispatchThread(Container.java:880)
     at org.apache.pivot.wtk.Component.invalidate(Component.java:1955)
     at 
org.apache.pivot.wtk.skin.ComponentSkin.invalidateComponent(ComponentSkin.java:340)
     at 
org.apache.pivot.wtk.skin.TextAreaSkinParagraphView.textRemoved(TextAreaSkinParagraphView.java:419)
     at 
org.apache.pivot.wtk.TextArea$Paragraph$ParagraphListenerList.textRemoved(TextArea.java:55)
     at 
org.apache.pivot.wtk.TextArea$Paragraph.removeText(TextArea.java:153)
     at org.apache.pivot.wtk.TextArea.insertText(TextArea.java:757)
     at org.apache.pivot.wtk.TextArea.insertText(TextArea.java:730)
     at 
cz.cgrim.alchemist.logger.TextAreaAppender.append(TextAreaAppender.java:41)
     at 
org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:251)
     at 
org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:66)
     at org.apache.log4j.Category.callAppenders(Category.java:206)
     at org.apache.log4j.Category.forcedLog(Category.java:391)
     at org.apache.log4j.Category.log(Category.java:856)
     at com.documentum.fc.common.DfLogger.warn(DfLogger.java:151)
     at 
com.documentum.fc.client.impl.bof.cache.ClassCacheManager$CacheCleanupTask.run(ClassCacheManager.java:602)
     at java.util.TimerThread.mainLoop(Timer.java:555)
     at java.util.TimerThread.run(Timer.java:505)

Here I simply implement AppenderSkeleton and append every line from 
LoggingEvent into Pivot's TextPane. Log4J runs it in separate thread.

Please, is now there another approach how to use threads and Pivot's 
Task to do changes in GUI or is it a bug? In 2.0 release everything 
spoken here worked like a charm.

Thanks for an advance.
Lukas Machacek
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