(defmacro pop-data (lock data-var queue &optional timeout)
  `(sb-thread:with-mutex (,lock)
    (loop :until ,data-var
       :do (or (sb-thread:condition-wait ,queue ,lock :timeout ,timeout)
	      ;; Lock not held, must unwind without touching *sites-data*.
	       (return-from pop-data nil)))
    (pop ,data-var)))


#|
scraper.lisp:47:18:
  error:
    return for unknown block: POP-DATA
    --> SB-THREAD:WITH-MUTEX SB-INT:DX-FLET FLET MULTIPLE-VALUE-PROG1 PROGN
    --> BLOCK LOOP BLOCK TAGBODY OR LET IF
    ==>
      (RETURN-FROM WITH-DRAKMA::POP-DATA NIL)


Compilation failed.
|#