Avoid waiting on DNS for more than 2 seconds to display the list of

nearby servers.  Use the IP address if no name arrives within that time.
We can't interrupt the requests, though, so we cache them, and if an
answer arrives after more than 2 seconds it will be used as soon as the
user reloads the page.

common/hostchooser.py

@@ -82,9 +82,8 @@ def find_servers(hostlist=[('127.0.0.1', None), ('<broadcast>', None)],
         for host, udpport in hostlist:
             print >> sys.stderr, '    %s,  UDP port %s' % (
                 host, udpport or ("%s (default)" % UDP_PORT))
-    servers = {}
     events = {}
-    aliases = {}
+    replies = []
     s = socket(AF_INET, SOCK_DGRAM)
     s.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
     for trynum in range(tries):
@@ -120,27 +119,41 @@ def find_servers(hostlist=[('127.0.0.1', None), ('<broadcast>', None)],
                 hostrecv.append(time.time())
             data = data.split(':')
             if len(data) >= 4 and data[0] == PONG_MESSAGE:
-                if data[2]:
-                    hostname = data[2]
-                else:
-                    hostname = answer_from[0]
-                    try:
-                        hostname = gethostbyaddr(hostname)[0]
-                        if hostname == 'localhost':
-                            from msgstruct import HOSTNAME as hostname
-                    except error:
-                        pass
                 try:
                     port = int(data[3])
                 except ValueError:
                     if port_needed:
                         continue
                     port = ''
-                result = (hostname, port)
-                servers[result] = ':'.join(data[1:2]+data[4:])
-                aliases[hostname] = ipaddr
+                if data[2]:
+                    hostname = data[2]
+                    realhostname = [hostname]
+                else:
+                    hostname = answer_from[0]
+                    realhostname = lazy_gethostbyaddr(hostname)
+                server = ':'.join(data[1:2]+data[4:])
+                replies.append((hostname, realhostname, port, server, ipaddr))
             else:
                 print >> sys.stderr, "got an unexpected answer from", answer_from
+    servers = {}
+    aliases = {}
+    timeout = time.time() + 2.0     # wait for gethostbyaddr() for 2 seconds
+    while replies:
+        i = 0
+        now = time.time()
+        while i < len(replies):
+            hostname, realhostname, port, server, ipaddr = replies[i]
+            if realhostname:
+                hostname = realhostname[0]    # got an answer
+            elif now < timeout:
+                i += 1     # must wait some more time
+                continue
+            result = (hostname, port)
+            servers[result] = server
+            aliases[hostname] = ipaddr
+            del replies[i]
+        if replies:
+            time.sleep(0.08)   # time for gethostbyaddr() to finish
     if verbose:
         print >> sys.stderr, "%d answer(s):" % len(servers), servers.keys()
     for host, port in servers.keys():
@@ -151,4 +164,29 @@ def find_servers(hostlist=[('127.0.0.1', None), ('<broadcast>', None)],
             if len(hostsend) == len(hostrecv) == tries:
                 ping = min([t2-t1 for t1, t2 in zip(hostsend, hostrecv)])
         servers[host, port] = (servers[host, port], ping)
+    sys.setcheckinterval(4096)
     return servers
+
+# ____________________________________________________________
+
+HOSTNAMECACHE = {}
+
+def _lazygetter(hostname, resultlst):
+    try:
+        try:
+            hostname = gethostbyaddr(hostname)[0]
+            if hostname == 'localhost':
+                from msgstruct import HOSTNAME as hostname
+        except error:
+            pass
+    finally:
+        resultlst.append(hostname)
+
+def lazy_gethostbyaddr(hostname):
+    try:
+        return HOSTNAMECACHE[hostname]
+    except KeyError:
+        resultlst = HOSTNAMECACHE[hostname] = []
+        import thread
+        thread.start_new_thread(_lazygetter, (hostname, resultlst))
+        return resultlst