Improve mutex for online_reps::sample () (#1672)
Improve mutex for online_reps::sample () (#1672)

* Improve mutex for online_reps::sample ()

* Better unordered_set naming

clemahieu/raiblocks,SergiySW/raiblocks,clemahieu/raiblocks,clemahieu/raiblocks,clemahieu/raiblocks,clemahieu/raiblocks,SergiySW/raiblocks,SergiySW/raiblocks,SergiySW/raiblocks,SergiySW/raiblocks,clemahieu/raiblocks