The macro with-hash-table-locked
evaluates body with the hash table hash-table locked against modification by other threads. The current thread can modify hash-table.
with-hash-table-locked
is useful not only for multiple accesses to the same table, but also when an access to the table must be consistent with some other operation, avoiding the need to make a separate lock,
gethash-ensuring
make-hash-table
modify-hash
with-ensuring-gethash
Atomicity and thread-safety of the LispWorks implementation
LispWorks User Guide and Reference Manual - 13 Feb 2015