guard memory storage with a oplock

[majst01]

like we do for sql databases to have same concurency stability

[codecov-commenter]

Codecov Report

Merging #60 (6a334ac) into master (04e73d8) will decrease coverage by 0.23%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master      #60      +/-   ##
==========================================
- Coverage   77.35%   77.11%   -0.24%     
==========================================
  Files           5        5              
  Lines         468      472       +4     
==========================================
+ Hits          362      364       +2     
- Misses         56       57       +1     
- Partials       50       51       +1     

Impacted Files	Coverage Δ
memory.go	90.90% <60.00%> (-4.10%)	⬇️

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