15.2.8.2 Accessing symbol values across processes

Use symeval-in-process to read the value of a dynamically bound symbol in a given process.

(setf mp:symeval-in-process) can set the value of such a symbol.

symeval-in-process is mostly intended for debugging. Do not call it while the thread is actually running.

LispWorks User Guide and Reference Manual - 21 Dec 2011