[ImageJ-devel] [fiji-devel] creating io.scif.img.ImgOpener currently fails in Fiji

[Curtis Rueden]

Hi Tobias,

> Except now all dependencies are not there anymore because now there
> are non-obvious (to me) implicit runtime dependencies.
>
> I find this unfortunate.

I agree that this is a two-edged sword. We have more types of plugins now,
which can alter the runtime behavior in more ways, so of course it becomes
possible for ill-behaved plugins to bring down the system.

This is already true in ImageJ 1.x though, because it is extensible at
runtime: any plugin class could have a static initializer block that hoses
up the JVM however it can imagine. It is just easier to do now.

IMO, it would not be worth it to eliminate these powerful extension points
just because of this possibility. The flexibility gained outweighs any
disadvantages.

We have already taken great pains to mitigate the issue with services in
the context: when you create a new ImgOpener without specifying an SJC
context, it uses _only_ relevant service types: things that implement the
SciJavaService and SCIFIOService interfaces. In other words: _not_
ImageJServices or other service types. The reason LegacyService is being
(erroneously!) pulled in here is due to a bug in the design of the SJC
AppEventService, as I said. I introduced a "LegacyAppEventService" which is
a SciJavaService but depends on the ImageJ LegacyService. Hence, any
Context that asks for SciJavaServices now pulls in a DefaultLegacyService
whenever the LegacyAppEventService is on the classpath. The fix is to stop
doing that.

Anyway, if it still bothers you that any ol' developer can add something to
the classpath which hoses up your programs, then you can stop it: create a
more carefully controlled SJC Context and pass that to the ImgOpener.
Alternately, we could change ImgOpener to be even more conservative in
which services it uses. Of course, there are downsides there: any
additional file format plugins, codec plugins, etc., might not be work
properly if they do not have access to the services they need.

I am very open to ideas for mitigating the extensibility issues here.

Regards,
Curtis


On Fri, Aug 22, 2014 at 9:35 AM, Tobias Pietzsch <pietzsch at mpi-cbg.de>
wrote:

> Hi Johannes,
>
> On 22 Aug 2014, at 09:04, Johannes Schindelin <Johannes.Schindelin at gmx.de>
> wrote:
>
> Hi Tobias,
>
> On Fri, 22 Aug 2014, Tobias Pietzsch wrote:
>
> Currently
> new io.scif.img.ImgOpener();
> fails with
> java.lang.IllegalArgumentException: Invalid service:
> net.imagej.legacy.LegacyAppEventService
>
>
> Yep, the explanation is very easy:
>
> [...]
> Caused by: java.lang.UnsupportedOperationException: Cannot instantiate
> more than one DefaultLegacyService
> […]
>
>
> I missed that...
>
>
> There is already a context, including a legacy service. Unfortunately, the
> best way to get at this context from an *ImageJ 1.x plugin* that I could
> come up with is:
>
> import org.scijava.Context;
>
> ...
>
> final Context context = (Context)
>  IJ.runPlugIn(Context.class.getName(), "");
> final ImgOpener opener = new ImgOpener(context);
>
> (There is no way to make that more convenient without letting SCIFIO
> depend on ImageJ 1.x, which is of course a big no-no).
>
>
> The problem with this solution you suggested is that it does not work in
> Eclipse:
> Exception in thread "main" java.lang.IllegalArgumentException: Invalid
> service: net.imagej.legacy.DefaultLegacyService
>
> As much as I understand the need for the runtime service discovery used by
> the scijava stack, there are certainly downsides to it.
> My feeling is that in some ways it undermines the advantages that we have
> gained by switching to maven.
> I can import a maven project into my Eclipse, and all the dependencies are
> there, explicitly and automatically, which is really very convenient.
> Except now all dependencies are not there anymore because now there are
> non-obvious (to me) implicit runtime dependencies.
> I find this unfortunate.
>
> That being said, I found a solution that works for now, both in Eclipse
> and in Fiji
>     final ImgOpener opener = new ImgOpener( new Context(
> SCIFIOService.class, AppService.class, StatusService.class ) );
> This avoids requiring the net.imagej.legacy.LegacyAppEventService.
> It seems to work, but I’m not sure: Are there any downsides to that?
>
> best regards,
> Tobias
>
>
> Of course, you could also turn your plugin into an ImageJ2 plugin -- which
> is handled properly in Fiji thanks to Fiji Just Being ImageJ2 -- and then
> it would become as easy as:
>
>  @Parameter
>  private IOService io;
>
>  ...
>   // use the IOService (which lets SCIFIO handle
>  // things) to open your dataset
>
> Ciao,
> Johannes
>
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