Availability:built-in
garbage_collect_atomsReclaim unused atoms. Normally invoked after agc_margin 
(a Prolog flag) atoms have been created. On multithreaded versions the 
actual collection is delayed until there are no threads performing 
normal garbage collection. In this case garbage_collect_atoms/0 
returns immediately. Note that there is no guarantee it will ever 
happen, as there may always be threads performing garbage collection.