Prevent error when JVM is already running.

[hadim]

See imagej/pyimagej#29 for details.

[hanslovsky]

I do not agree that this check should be the responsibility of scyjava. As a (fairly) low-level library that does not do any UI work itself, I think that scyjava should fail if used incorrectly. The exception holds valuable information about improper use, which might get lost if only a warning is emitted and the python logging system has not been initialized.

What is the reasoning for not checking for the ValueError exception down-stream? If that exception is too broad, we could create a new exception and re-throw.

[hadim]

I understand your point.

But running twice the same line without modifying anything else and get an error only the second time is definitively not the correct pattern in my opinion.

I know the scyjava/pyimage/jnius init mechanism is complex but we should be able to run (or the equivalent scyjava code):

import imagej
imagej.init()

twice without running into an error.

Do you guys (@ctrueden and @hanslovsky) think this issue could be addressed elsewhere? Or do you think that issue should only be handled at the user level?

[hanslovsky]

But running twice the same line without modifying anything else and get an error only the second time is definitively not the correct pattern in my opinion.

I agree but that is a general problem with (stateful) singletons: Running the same thing multiple times will produce different result depending on the global state.

Do you guys hink this issue could be addressed elsewhere?

imagej.init() looks like a good candidate to me. The scyjava_config portion of the code could be run only if pyjnius is not initialized.

[hadim]

For the record: imagej/pyimagej#30

[hanslovsky]

Thanks @hadim