Re: Why does JDK 1.6 recommend creating Swing components on the EDT?

Nigel Wade <>
Mon, 7 Dec 2009 15:08:29 +0000 (UTC)
On Tue, 01 Dec 2009 10:32:24 +0100, Albert wrote:

Le 01/12/2009 09:54, Roedy Green a ??crit :

On Mon, 30 Nov 2009 13:39:07 -0800, markspace<>
wrote, quoted or indirectly quoted someone who said :

Yeah, Sun fuggered up their earlier recommendation and had to take it
back. Everything goes on the EDT now.

The problem is threading bugs are very hard to reproduce and track
down. My putting everything onto the EDT thread, they avoid a large
number of headaches.

have you actually seen such a bug ? Something like corrupted data in a
swing model for example ? I've never triggered such a bug, even if i did
a lot of gui calls off the EDT.

Yes, I have encountered such a bug. Just because you've never actually
experienced the problem does not mean that the problem does not exist, or
that it's safe to ignore it. You can never know when the bug will strike,
and this makes them almost impossible to track down. The symptoms vary,
as do their timing. It may run perfectly 99 times out of a 100. Or it may
work perfectly every time on one system, but fail on another.

In my case the GUI worked perfectly - most of the time. But every once in
a while some of the components were not drawn correctly when the GUI
first appeared. The components which were not fully drawn varied.

At that time the recommendation from Sun, as explained in the Java Swing
Tutorial, was that it was safe to create the GUI on the main thread until
such time as the first component was realized, when the EDT would be
started. From this point on (once the EDT was running) all subsequent use
of any Swing component should be done on the EDT. It was around the same
time as I was having my problem that Sun changed their advice on this
issue (and also updated the Tutorial - this was the 1.4/1.5 Tutorial,
prior to the re-write for 1.6). So I altered my code to follow their
advice and the problem went away, never to be seen again.

IIRC, Sun explained this by saying that certain components may, during
construction, perform operations which caused the EDT to be started even
though they had not yet been realized. Rather than working through the
source code for every single component to check what operations its
constructor performed and whether they started the EDT (and updating the
Javadocs accordingly), it was simpler just to advise that all components
should be constructed on the EDT.

Nigel Wade

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