[mcclim-devel] Threading and Waiting

[John Connors]

While looking for the 'right' way to get a SCBL thread to wait for a specified 
condition as part of an attempt to update port from the CLOCC, I came across 
this gem in the McCLIM sources.

(declaim (inline yield))
(defun yield ()
   (declare (optimize speed (safety 0)))
   (sb-alien:alien-funcall
    (sb-alien:extern-alien "sched_yield" (function sb-alien:int)))
   (values))

(defun process-wait (reason predicate)
   (let ((old-state (process-whostate *current-process*)))
     (unwind-protect
	 (progn
	   (setf old-state (process-whostate *current-process*)
		 (process-whostate *current-process*) reason)
	   (loop
	    (let ((it (funcall predicate)))
	      (when it (return it)))
	    ;(sleep .01)
                (yield)))
       (setf (process-whostate *current-process*) old-state))))

Now this will work, but my understanding is when calling sched_yeild, a thread 
gets completely expired and put at the back of the scheduling queue. What was/is 
wrong with sleep?