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Re: Canvas Wanted (simple question)

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On 12/24/2011 5:16 AM, Joerg Meier wrote:
> On Fri, 23 Dec 2011 21:42:51 -0800, markspace wrote:
>
>> On 12/23/2011 6:41 PM, Joerg Meier wrote:
>>> Only you clearly didn't read my post other farther than "doesn't need to be
>>> wrapped".
>> Yes I clearly did, and I clearly explained why your assumption was
>> incorrect.
>
> Then what you said makes no sense. Events will fire on a thread before the
> thread exists ? How's that work ?


In the case where callbacks are made on the EDT, they'll be asynchronous 
with the main thread and won't wait for the "setVisibile()" call. 
You'll be still constructing objects on the main thread and the EDT will 
be running and trying to manipulate those objects at the same time.

You have no real control over the EDT, it fires when it wants to.  It 
isn't going to actually wait for you to call setVisibile(), and it 
really never did.  That was a mistake in the Java documentation to claim 
that the EDT did wait for setVisible().

Here's a question for you now:  read the section of the JLS on the Java 
memory model.  When the main thread starts and creates objects like a 
JFrame, those objects write to main memory as they are constructed.  How 
are those write synchronized with the EDT, esp. with regard to the 
visibility of those writes?

Main                             EDT

call new JFrame
   write to main memeory
call new JPanel
   write to main memory
call setVisible
   --------------------------->
                                read JFrame object
                                read JPanel object

These reads don't have any explicit synchronization if you construct 
them like shown.  There's no guaranteed visibility, and seeing partially 
constructed objects is a big possibility.  As a practical matter, I know 
how the EDT starts and the chance of a data race is small, but because 
that's not guaranteed by the documentation, it really really bad 
practice.  Relying on undocumented internal implementations is grossly 
unprofessional.

And all the Swing documentation says not to do this; you're explicitly 
told to create all Swing objects on the EDT, not main or any other 
thread.  So it's bad practice times two.

This information is at least five years old, because it was definitely 
there for Java 6.  Please refer to some current documentation, you're 
basically quoting Java 4 and that's nine years old, nearly a decade now.

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Thread

Canvas Wanted (simple question) Paweł Lampe <scony@sconysoft.com> - 2011-12-11 22:02 +0000
  Re: Canvas Wanted (simple question) Knute Johnson <nospam@knutejohnson.com> - 2011-12-11 15:55 -0800
    Re: Canvas Wanted (simple question) Joerg Meier <joergmmeier@arcor.de> - 2011-12-24 01:49 +0100
      Re: Canvas Wanted (simple question) markspace <-@.> - 2011-12-23 17:26 -0800
        Re: Canvas Wanted (simple question) Joerg Meier <joergmmeier@arcor.de> - 2011-12-24 03:41 +0100
          Re: Canvas Wanted (simple question) markspace <-@.> - 2011-12-23 21:42 -0800
            Re: Canvas Wanted (simple question) Joerg Meier <joergmmeier@arcor.de> - 2011-12-24 14:16 +0100
              Re: Canvas Wanted (simple question) markspace <-@.> - 2011-12-24 06:47 -0800
      Re: Canvas Wanted (simple question) Knute Johnson <nospam@knutejohnson.com> - 2011-12-23 21:21 -0800
        Re: Canvas Wanted (simple question) markspace <-@.> - 2011-12-23 21:48 -0800
      Re: Canvas Wanted (simple question) Joerg Meier <joergmmeier@arcor.de> - 2011-12-24 14:20 +0100
        Re: Canvas Wanted (simple question) "John B. Matthews" <nospam@nospam.invalid> - 2011-12-24 11:22 -0500
  Re: Canvas Wanted (simple question) Roedy Green <see_website@mindprod.com.invalid> - 2011-12-12 09:58 -0800
  Re: Canvas Wanted (simple question) Paweł Lampe <scony@sconysoft.com> - 2011-12-14 15:57 +0000
    Re: Canvas Wanted (simple question) Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-12-14 10:21 -0800

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