Re: updating an ImageIcon's backing BufferedImage content from multiple threads

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 05 Apr 2009 21:53:07 -0700

Message-ID:

<49d98aa4$0$19548$b9f67a60@news.newsdemon.com>

John B. Matthews wrote:

In article
<fa7cd57f-39be-4f4b-b8e6-1a3213ab8b35@f19g2000yqo.googlegroups.com>,
cbossens73@yahoo.fr wrote:

On Apr 6, 12:48 am, Lew <no...@lewscanon.com> wrote:

Knute Johnson wrote:

[...]

All this is fascinating :)

Indeed. I often turn to the Memory Consistency Properties summary found
in java.util.concurrent, noting "The results of a write by one thread
are guaranteed to be visible to a read by another thread only if the
write operation happens-before the read operation. [...] A call to start
on a thread happens-before any action in the started thread":

<http://java.sun.com/javase/6/docs/api/java/util/concurrent/package-summa
ry.html>

The latter condition can be met by having the buffer-modifying thread
call java.awt.EventQueue.invokeLater(), which runs its argument
asynchronously on the EDT:

<http://java.sun.com/javase/6/docs/api/java/awt/EventQueue.html>

I believe the notification sent by javax.swing.Timer also runs on the
EDT, thus satisfying the same requirement:

<http://java.sun.com/javase/6/docs/api/javax/swing/Timer.html>

Often, modifying the buffer is the more time consuming operation, while
drawing the buffer's contents can proceed quickly without congesting the
EDT.

John:

Do you think that a thread enqueueing(sp) an event on the EDT with
invokeLater() produces a happens before relationship with that thread
even though Thread.start() is not called? Could that same mechanism
work in calls to repaint()?

--

Knute Johnson
email s/nospam/knute2009/

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