[ImageJ-devel] IJ2 - headless operation

[Curtis Rueden]

Hi Lee,

> how should I start ImageJ headless

It sounds like you want a full-featured ImageJ context with all available
services except for maybe a couple of them (the ones that touch AWT).

The easiest way to ensure your ImageJ context is headless is to exclude
problematic JARs from your distribution completely. Specifically: do not
include ij-legacy or any of the ij-ui-* UI implementations (e.g.,
ij-ui-swing).

Then you can create an ImageJ context simply with "new imagej.ImageJ()"
(note that this invocation changed a couple of days ago from the previous
static "imagej.ImageJ.createContext()" but it is otherwise the same).

If for some reason you need or want to include those problematic JARs in
your classpath, you can still avoid the ImageJ context including them by
passing an explicit list of services to the ImageJ constructor. Or, if you
would rather approach it from an "exclusion" rather than "inclusion"
standpoint, you could do something like:

  final PluginIndex pluginIndex = new PluginIndex();
  pluginIndex.discover();
  final List<PluginInfo<Service>> services = pluginIndex.getPlugins(Service.
class);

And then cherry-picking everything from the list that doesn't violate your
exclusion rules.

For that latter approach though, we should probably provide some helper
routine somewhere to make this easier; if you take a look at
ServiceHelper#findServiceClasses, you'll see the code, but it's currently
private. We could make that a public static utility method for you instead.
Or provide something even higher level.

> how headless is headless?

Ideally, we want headless to truly mean no usage of AWT whatsoever. That
said, we do violate that rule in one big place right now: the
ThreadService. The DefaultThreadService uses java.awt.EventQueue to queue
and invoke operations. With a normal JVM with java.awt.headless=true, this
is unlikely to cause problems. But if it does for some reason, you could
provide your own ThreadService implementation with a higher priority than
that of DefaultThreadService, and the ImageJ service loader will
automagically use it instead.

Regards,
Curtis


On Fri, Dec 14, 2012 at 3:09 PM, Lee Kamentsky <leek at broadinstitute.org>wrote:

>
>
> Hi all,
> I'm getting pretty far along with the CellProfiler integration and I'm
> at the point where I'd like to get a headless ImageJ context. My first
> guess was that I should call imagej.ImageJ.createContext() with a list
> containing only the ConsoleService.  The list (see below) has most of
> what I want (module service, command service, dataset service, display
> service), but is missing a few others (overlay service and scripting
> service). I've been running ImageJ with the DefaultUIService while
> running CellProfiler with a UI and it seems to operate pretty smoothly -
> some error messages when it can't find viewers for displays, but
> otherwise without any apparent UI interaction.
>
> So my first question is how should I start ImageJ headless and my second
> question is "how headless is headless?" (will it ever touch AWT? Will it
> exclude the legacy layer?).
>
> Created service: imagej.thread.**DefaultThreadService
> Created service: imagej.event.**DefaultEventService
> Created service: imagej.plugin.**DefaultPluginService
> Created service: imagej.module.**DefaultModuleService
> Created service: imagej.command.**DefaultCommandService
> Created service: imagej.options.**DefaultOptionsService
> Created service: imagej.event.**DefaultStatusService
> Created service: imagej.object.**DefaultObjectService
> Created service: imagej.data.**DefaultDatasetService
> Created service: imagej.io.DefaultIOService
> Created service: imagej.display.**DefaultDisplayService
>
>
>
>
>
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