Acquire Lock Algorithm - lucienlazar/plsql-application-locking GitHub Wiki
The three types of locks handled by the framework
Shared (S)
used for reading;
shared locks can be acquired when other shared or write exclusive locks already exist on the resource;
cannot be acquired when a full exclusive lock already exists on the resource.
Write exclusive (WX)
used for writing;
write exclusive locks can be acquired when shared locks already exist on the resource;
cannot be acquired when other write exclusive or full exclusive lock already exist on the resource.
Full exclusive (FX)
strictly exclusive;
can be acquired only when no other locks exist on the resource.