fix memory leak

[muzuro]

I noticed a memory leak in my production environment. It can be reproduced with custom TransportCosts and huge array in it(after some amount of invocation same vrp, without stopping jsprit jvm and transportCost should be created each invocation, you wil recieve OOM). If we don`t remove shutdown hook it will be stored in runtime.

[oblonski]

Great. Thanks a lot @muzuro. Let me reproduce this first and recall why we actually need this hook ;).

[oblonski]

You are absolutely correct. Could reproduce is. This is evil. Thank you very much.

[karussell]

Additionally I would move the addition to the shutdown into the if. IMO something 'external' should not be manipulated.

[oblonski]

already done 👍 . thanks.

[karussell]

BTW1: Wouldn't it then make sense to have just one listener and add

Runtime.getRuntime().removeShutdownHook(hook);

BTW2: here is the problematic leaking explained for inner non-static classes

[oblonski]

Heap memory before and after fix :)