Fix img loaders for spark

[trautmane]

Hi @tpietzsch and @StephanPreibisch,

These commits fix the "could not find XmlIoBasicImgLoader implementation for format bdv.n5" issue @boazmohar identified in JaneliaSciComp/BigStitcher-Spark#2 . The first commit fixes the core problem. The second commit contains slf4j logging calls I added to help confirm what was happening. The logging works well in the spark environment I used for testing, but I wasn't sure if it would cause trouble for other contexts in which spimdata is used. Hopefully, separating the commits makes it easier for you to toss the logging stuff if necessary.

Best,
Eric

[StephanPreibisch]

Hi @trautmane, that is great, thanks so much!! ... but I don't think it is good to have a log4j dependency in such a basic repo, what do you think @tpietzsch?

[trautmane]

Note that the logging dependency is on the slf4j api (not log4j) so it will use whatever logger is bound in by the application using spimdata. If no logger implementation exists, a warning message will be printed upon first reference and then nothing else is logged ( see https://www.slf4j.org/manual.html ).

[tpietzsch]

Thanks @trautmane!

The registerManually method should be synchronised too probably?
And maybe we should use ConcurrentHashMaps instead of the HashMaps?

@StephanPreibisch I'm not fundamentally opposed to adding logging to the repo, but I also have a slight preference not do it now. Let's keep it on a branch, and next time it proves as useful as here, we merge it in?

[tpietzsch]

And maybe we should use ConcurrentHashMaps instead of the HashMaps?

I did this, and moved the initial non-synchronized if ( !buildWasCalled ) inside the build() method.
I pushed to the origin/fix_img_loaders_for_spark branch.
@trautmane @StephanPreibisch Could you verify that this still solves your problem and I didn't make any stupid mistake? If it works, I'll merge and release.

I put the slf4j commit on a branch origin/add-logging (which I would not merge for the release).

[trautmane]

Hi @tpietzsch - I think your change will still work but I prefer the way I had it (hah - no surprise there :). Maybe I am misunderstanding something. Let's discuss when we meet with @StephanPreibisch at 10am EST today.

[tpietzsch]

@trautmane I changed it back to how you had it, and merged via origin/fix_img_loaders_for_spark. Releasing now...