Posted by
dscho on
Jun 14, 2007; 3:21am
URL: http://imagej.273.s1.nabble.com/Headless-ImageJ-tp3699125.html
Hello community,
recently the problem cropped up in a discussion with fellow developers,
how to run a batch macro on a machine (such as a node on a
cluster[*1*]...) that does not have any graphics environment installed.
[if you're interested only in the solution, you might want to skip forward
to the short explanation...]
<warning: detailed explanation on Java level follows>
At least on Linux, such a batch run will inevitably stop early, namely
when the class ij.Menus tries to instantiate a Menu. For some reason, it
seems, the Java developers decided in their infinite wisdom that a Menu
cannot live without a graphics environment. Even if you don't ever show
the Menu.
Oh, well.
I tried to get rid of the java.awt.Menu instances, but realized then, that
most plugins use a GenericDialog, which is directly derived from
java.awt.Dialog. An indeed, Java refuses to instantiate a Dialog (even if
it is never shown!) in the absence of a graphics environment.
But then, there _are_ plugins out in the wild, which depend on
GenericDialog to be derived from java.awt.Dialog, because they actually
update some preview or do other stuff that cannot be done directly with
the methods of the GenericDialog.
So there is the dilemma. Some plugins will not run _without_ GenericDialog
being a java.awt.Dialog, and headless operation will _not_ run _with_
GenericDialog being a java.awt.Dialog.
</warning>
A workaround, if you do not use any plugins that manipulate the
java.awt.Dialog directly (there are only a few out there, you know who you
are!), is to replace both ij.Menus and ij.gui.GenericDialog by classes
that will not instantiate anything graphical.
This workaround is available as "headless.jar", to be prepended to
the classpath, available from
http://sourceforge.net/imageja/ in
binary form, or in source from from branch "headless" on
http://repo.or.cz/imageja.git.
Whew. That was a long explanation.
Short explanation:
To start a batch macro on a machine without graphics environment, you have
to download
http://downloads.sourceforge.net/imageja/headless.jar?use_mirror=osdnand prepend the downloaded "headless.jar" to the classpath before ij.jar,
like this:
java -classpath headless.jar:ij.jar ij.ImageJ -batch <macro>
On Windows, you have to replace the ":" between "headless.jar" and
"ij.jar" by a ";", although you are much more unlikely to run something
headlessly on Windows.
Somehow, I seem to be unable to come up with a better solution. If someone
has an idea how to do it in a less ugly way, please enlighten me.
Ciao,
Dscho
[*1*] ... and I mean a cluster here. Not something Microsoft conveniently
redefined to be a hot standby. No, a real cluster. Microsoft calls it a
grid. But it used to be called a cluster until recently.