Rewrite pending() to handle input and output.

Pending does reads and writes.  In the case of server startup, we may
need to write out zeoVerify() messages.  Always check for read status,
but don't check for write status only there is output to do.  Only
continue in this loop as long as there is data to read.

src/ZEO/zrpc/connection.py

@@ -460,7 +460,7 @@ class Connection(smac.SizedMessageAsyncConnection):
         else:
             asyncore.poll(0.0, self._map)
 
-    def pending(self):
+    def pending(self, timeout=0):
         """Invoke mainloop until any pending messages are handled."""
         if __debug__:
             self.log("pending(), async=%d" % self.is_async(), level=zLOG.TRACE)
@@ -468,26 +468,50 @@ class Connection(smac.SizedMessageAsyncConnection):
             return
         # Inline the asyncore poll() function to know whether any input
         # was actually read.  Repeat until no input is ready.
-        # XXX This only does reads.
-        r_in = [self._fileno]
-        w_in = []
+
+        # Pending does reads and writes.  In the case of server
+        # startup, we may need to write out zeoVerify() messages.
+        # Always check for read status, but don't check for write status
+        # only there is output to do.  Only continue in this loop as
+        # long as there is data to read.
+        r = r_in = [self._fileno]
         x_in = []
-        while 1:
+        while r and not self.closed:
+            if self.writable():
+                w_in = [self._fileno]
+            else:
+                w_in = []
             try:
-                r, w, x = select.select(r_in, w_in, x_in, 0)
+                r, w, x = select.select(r_in, w_in, x_in, timeout)
             except select.error, err:
                 if err[0] == errno.EINTR:
+                    timeout = 0
                     continue
                 else:
                     raise
-            if not r:
-                break
-            try:
-                self.handle_read_event()
-            except asyncore.ExitNow:
-                raise
-            except:
-                self.handle_error()
+            else:
+                # Make sure any subsequent select does not block.  The
+                # loop is only intended to make sure all incoming data is
+                # returned.
+
+                # XXX What if the server sends a lot of invalidations,
+                # such that pending never finishes?  Seems unlikely, but
+                # not impossible.
+                timeout = 0
+            if r:
+                try:
+                    self.handle_read_event()
+                except asyncore.ExitNow:
+                    raise
+                except:
+                    self.handle_error()
+            if w:
+                try:
+                    self.handle_write_event()
+                except asyncore.ExitNow:
+                    raise
+                except:
+                    self.handle_error()
 
 class ManagedServerConnection(Connection):
     """Server-side Connection subclass."""