Fixed a serious bug that could cause client I/O to stop

(hang). This was accomonied by a critical log message along the
lines of: "RuntimeError: dictionary changed size during iteration".

NEWS.txt

-What's new on ZODB 3.7.0c1?
-===========================
+What's new on ZODB 3.7.1?
+=========================
 
 Packaging
 ---------
@@ -19,6 +19,10 @@ Packaging
 ClientStorage
 -------------
 
+- (3.7.1) Fixed a serious bug that could cause client I/O to stop
+  (hang). This was accomonied by a critical log message along the
+  lines of: "RuntimeError: dictionary changed size during iteration".
+
 - (3.7b4) Added logic to avoid spurious errors from the logging system
   on exit.
 

src/ZEO/zrpc/connection.py

@@ -52,8 +52,12 @@ def client_loop():
     
     while map:
         try:
-            r = e = list(client_map)
-            w = [fd for (fd, obj) in map.iteritems() if obj.writable()]
+            
+            # The next two lines intentionally don't use
+            # iterators. Other threads can close dispatchers, causeing
+            # the socket map to shrink.
+            r = e = client_map.keys()
+            w = [fd for (fd, obj) in map.items() if obj.writable()]
 
             try:
                 r, w, e = select.select(r, w, e, client_timeout)