The rules and users are stored in thread-local pointers which removes the
need to hold global locks. This allows greater scalability but causes a
slightly larger memory footprint. Usually the increase in memory
consumption is trivial compared to the benefits in scaling.
Using a per-thread rule and user list allows changes to be applied
immediately without locking on the instance level.
The updating of the rules uses the new functinality described in the
debugcmd.h header. The module registers two functions at startup; one for
reloading rules and one for printing them. These custom functions can be
seen in the `maxadmin list functions` output.
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