f-fix-deadlock -> dev

Summary

fix #122 (closed)

Focus

Problem was a non-atomic operation (integer decrement). Concurrent reading thread would fail to decrement the acquired counter. See code annotations.

Test Environment

Please use b2faf630 to see failing tests. Please use 9b85d817 for fixed DatabaseAccessManager

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CHANGELOG.md

@@ -25,6 +25,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+* #122 - Dead-lock due to error in the DatabaseAccessManager.
 * #120 - Editing entities that were created with a no longer existing user
   leads to a server error.
 * #31 - Queries with keywords in the path (e.g. `... STORED AT 0in.txt`)