fix(AutoReloadAssetTypeManager): synchronize methods to avoid NPE

[keturn]

switchEnvironment leaves a closed reloadOnChangeHandler for a moment, which caused reloadChangedAssets() to crash if called from another thread.

I don't believe this is the most efficient locking strategy for this, but the ergonomics of marking methods as synchronized are so much better than using Lock.lock(). I tried a few other things but they added a ton of noise to the code, so I decided to submit this more readable version until we find something wrong with it.

I have very little experience managing thread safety in Java and am extra open to suggestions on this one.

Blocks MovingBlocks/Terasology#4622

Test plan

MTE tests run under MovingBlocks/Terasology#4622 consistently crash without a fix for this. Should be able to reproduce with something like

./gradlew :modules:Health:integrationTest

[jdrueckert]

Sounds reasonable to me. However, I likely have even less experience with thread safety in Java, so feel free to wait for a review from somebody else 😅

[keturn]

Sounds reasonable to me. However, I likely have even less experience with thread safety in Java, so feel free to wait for a review from somebody else 😅

It's a topic that's worth some attention, but I get the feeling I should not hold my breath for it.

I rate this as a low-risk change, so I'm going to go ahead and merge it.

If we find reloadChangedAssets causing things to stutter we can come back and give it another look.