Previously, processing a large batch of timeouts was O(n^2) in the number of

outstanding queries, and processing a DNS response packet was O(n) in the
number of outstanding queries. To speed things up in Google, we added a few circular,
doubly-linked lists of queries that are hash-bucketed based on
the attributes we care about, so most important operations are now O(1).

It might be that the number of buckets are higher than most people would need,
but on a quick calculation it should only be 100kB or so even on a 64-bit
system, so I've let it stay as-is.

1 files changed, 4 insertions, 1 deletions

diff --git a/ares_fds.c b/ares_fds.c
index a305b3b..4c6299a 100644
--- a/ares_fds.c
+++ b/ares_fds.c
@@ -30,6 +30,9 @@ int ares_fds(ares_channel channel, fd_set *read_fds, fd_set *write_fds)
   ares_socket_t nfds;
   int i;
 
+  /* Are there any active queries? */
+  int active_queries = !ares__is_list_empty(&(channel->all_queries));
+
   nfds = 0;
   for (i = 0; i < channel->nservers; i++)
     {
@@ -37,7 +40,7 @@ int ares_fds(ares_channel channel, fd_set *read_fds, fd_set *write_fds)
       /* We only need to register interest in UDP sockets if we have
        * outstanding queries.
        */
-      if (channel->queries && server->udp_socket != ARES_SOCKET_BAD)
+      if (active_queries && server->udp_socket != ARES_SOCKET_BAD)
         {
           FD_SET(server->udp_socket, read_fds);
           if (server->udp_socket >= nfds)