Fix PR#5309: Queue.add is not thread/signal safe

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@12163 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

1 files changed, 3 insertions, 2 deletions

diff --git a/stdlib/queue.ml b/stdlib/queue.ml
index 4e12eb3d2..388a46c53 100644
--- a/stdlib/queue.ml
+++ b/stdlib/queue.ml
@@ -54,12 +54,12 @@ let clear q =
   q.tail <- Obj.magic None
 
 let add x q =
-  q.length <- q.length + 1;
-  if q.length = 1 then
+  if q.length = 0 then
     let rec cell = {
       content = x;
       next = cell
     } in
+    q.length <- 1;
     q.tail <- cell
   else
     let tail = q.tail in
@@ -68,6 +68,7 @@ let add x q =
       content = x;
       next = head
     } in
+    q.length <- q.length + 1;
     tail.next <- cell;
     q.tail <- cell