update LIST-QUEUE-CONTENTS docstring, add note

diff --git a/NEWS b/NEWS
index 8985a10..e717e47 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -27,6 +27,8 @@ changes relative to sbcl-1.1.4:
   * enhancement: test-suite results are colorized, failures in red, unexpected
     success in green. Works on Windows and on terminals with ANSI escape code
     support. Can be disabled with --no-color.
+  * optimization: SB-CONCURRENCY:QUEUE implementation is more efficient.
+    (thanks to James M. Lawrence)
   * bug fix: no more unused variable style warnings from RESTART-CASE
     macroexpansion (lp#1113859)
   * bug fix: no more unused variable style warnings when loading

diff --git a/contrib/sb-concurrency/queue.lisp b/contrib/sb-concurrency/queue.lisp
index 397e29e..9b0949e 100644 (file)
--- a/contrib/sb-concurrency/queue.lisp
+++ b/contrib/sb-concurrency/queue.lisp
@@ -92,6 +92,8 @@ and secondary value."
                       (return (values value t)))))))))
 
 (defun try-walk-queue (fun queue)
+  ;; This isn't /quite/ as bad as it looks. We're in danger of needing
+  ;; to restart only as long as we're close to the head of the queue.
   (let ((node (queue-head queue)))
     (loop
        (let ((value (car node)))
@@ -105,8 +107,9 @@ and secondary value."
 
 (defun list-queue-contents (queue)
   "Returns the contents of QUEUE as a list without removing them from the
-QUEUE. Mainly useful for manual examination of queue state, as the list
-may be out of date by the time it is returned."
+QUEUE. Mainly useful for manual examination of queue state, as the list may be
+out of date by the time it is returned, and concurrent dequeue operations may
+in the worse case force the queue-traversal to be restarted several times."
   (tagbody
    :retry
      (collect ((result))