When I start CCL with latest Slime, the lx86cl64 process uses 100% CPU time, even when Slime is otherwise idle. REPL works as expected, except for high CPU load. I can drop CPU load back to 0%, if I change timeout from 1 to 100 like this --- swank-ccl.lisp 26 Mar 2012 15:09:57 -0000 1.27 +++ swank-ccl.lisp 1 Jul 2012 01:39:52 -0000 @@ -761,7 +761,7 @@ (nconc (ldiff q tail) (cdr tail))) (return (car tail))))) (when (eq timeout t) (return (values nil t))) - (ccl:timed-wait-on-semaphore (mailbox.semaphore mbox) 1)))) + (ccl:timed-wait-on-semaphore (mailbox.semaphore mbox) 100)))) (let ((alist '()) (lock (ccl:make-lock "register-thread"))) My CCL had not been updated for a while, so it could be bug in CCL, I'll try latest SVN build of CCL next Regards, Max