Race condition in KeyLocker

[Yrlec]

Thank you for creating this great library!

I found a potential race condition on this line in KeyLocker:

Paper/paperdb/src/main/java/io/paperdb/KeyLocker.java

Line 29 in 0e4e76a

if (!semaphoreMap.containsKey(key)) {

One should use putIfAbsent instead. See https://stackoverflow.com/a/15850870/71354 for an explanation.

[pilgr]

@Yrlec Good catch, thanks!