Archive thread safety

[AndreasAlbert]

(Related to #41)

Hi,

is there any documentation on which archives are thread safe? Specifically, I'd like to have multiple processes write to the same serialized dir_archive. I'd assume this works fine if I can guarantee that no two processes ever touch the same key, but I am not certain.

Thanks

[mmckerns]

is there any documentation on which archives are thread safe?

Documentation... no, but there should be. I'll add a note to #41