Merge pull request #2809 from sigiesec/optimize-select-win

Optimize select on Windows; reduce code duplication in select_t

src/select.cpp

@@ -54,10 +54,13 @@ zmq::select_t::select_t (const zmq::ctx_t &ctx_) :
     current_family_entry_it (family_entries.end ()),
 #else
     maxfd (retired_fd),
-    retired (false),
 #endif
     stopping (false)
 {
+#if defined ZMQ_HAVE_WINDOWS
+    for (size_t i = 0; i < fd_family_cache_size; ++i)
+        fd_family_cache [i] = std::make_pair (retired_fd, 0);
+#endif
 }
 
 zmq::select_t::~select_t ()
@@ -74,13 +77,12 @@ zmq::select_t::handle_t zmq::select_t::add_fd (fd_t fd_, i_poll_events *events_)
 #if defined ZMQ_HAVE_WINDOWS
     u_short family = get_fd_family (fd_);
     wsa_assert (family != AF_UNSPEC);
-    family_entry_t& family_entry = family_entries [family];
+    family_entry_t &family_entry = family_entries [family];
+#endif
     family_entry.fd_entries.push_back (fd_entry);
     FD_SET (fd_, &family_entry.fds_set.error);
-#else
-    fd_entries.push_back (fd_entry);
-    FD_SET (fd_, &fds_set.error);
 
+#if !defined ZMQ_HAVE_WINDOWS
     if (fd_ > maxfd)
         maxfd = fd_;
 #endif
@@ -103,6 +105,47 @@ zmq::select_t::find_fd_entry_by_handle (fd_entries_t &fd_entries,
     return fd_entry_it;
 }
 
+void zmq::select_t::trigger_events (const fd_entries_t &fd_entries_,
+                                    const fds_set_t &local_fds_set_,
+                                    int event_count_)
+{
+    //  Size is cached to avoid iteration through recently added descriptors.
+    for (fd_entries_t::size_type i = 0, size = fd_entries_.size ();
+         i < size && event_count_ > 0; ++i) {
+        const fd_entry_t &current_fd_entry = fd_entries_ [i];
+
+        if (is_retired_fd (current_fd_entry))
+            continue;
+
+        if (FD_ISSET (current_fd_entry.fd, &local_fds_set_.read)) {
+            current_fd_entry.events->in_event ();
+            --event_count_;
+        }
+
+        //  TODO: can the is_retired_fd be true at this point? if it
+        //  was retired before, we would already have continued, and I
+        //  don't see where it might have been modified
+        //  And if rc == 0, we can break instead of continuing
+        if (is_retired_fd (current_fd_entry) || event_count_ == 0)
+            continue;
+
+        if (FD_ISSET (current_fd_entry.fd, &local_fds_set_.write)) {
+            current_fd_entry.events->out_event ();
+            --event_count_;
+        }
+
+        //  TODO: same as above
+        if (is_retired_fd (current_fd_entry) || event_count_ == 0)
+            continue;
+
+        if (FD_ISSET (current_fd_entry.fd, &local_fds_set_.error)) {
+            current_fd_entry.events->in_event ();
+            --event_count_;
+        }
+    }
+}
+
+#if defined ZMQ_HAVE_WINDOWS
 bool zmq::select_t::try_remove_fd_entry (
   family_entries_t::iterator family_entry_it, zmq::fd_t &handle_)
 {
@@ -126,6 +169,7 @@ bool zmq::select_t::try_remove_fd_entry (
     family_entry.fds_set.remove_fd (handle_);
     return true;
 }
+#endif
 
 void zmq::select_t::rm_fd (handle_t handle_)
 {
@@ -151,21 +195,21 @@ void zmq::select_t::rm_fd (handle_t handle_)
     }
 #else
     fd_entries_t::iterator fd_entry_it =
-      find_fd_entry_by_handle (fd_entries, handle_);
+      find_fd_entry_by_handle (family_entry.fd_entries, handle_);
     assert (fd_entry_it != fd_entries.end ());
 
     fd_entry_it->fd = retired_fd;
-    fds_set.remove_fd (handle_);
+    family_entry.fds_set.remove_fd (handle_);
 
     if (handle_ == maxfd) {
         maxfd = retired_fd;
-        for (fd_entry_it = fd_entries.begin (); fd_entry_it != fd_entries.end ();
-              ++fd_entry_it)
+        for (fd_entry_it = family_entry.fd_entries.begin ();
+             fd_entry_it != family_entry.fd_entries.end (); ++fd_entry_it)
             if (fd_entry_it->fd > maxfd)
                 maxfd = fd_entry_it->fd;
     }
 
-    retired = true;
+    family_entry.retired = true;
 #endif
     adjust_load (-1);
 }
@@ -175,10 +219,9 @@ void zmq::select_t::set_pollin (handle_t handle_)
 #if defined ZMQ_HAVE_WINDOWS
     u_short family = get_fd_family (handle_);
     wsa_assert (family != AF_UNSPEC);
-    FD_SET (handle_, &family_entries [family].fds_set.read);
-#else
-    FD_SET (handle_, &fds_set.read);
+    family_entry_t &family_entry = family_entries [family];
 #endif
+    FD_SET (handle_, &family_entry.fds_set.read);
 }
 
 void zmq::select_t::reset_pollin (handle_t handle_)
@@ -186,10 +229,9 @@ void zmq::select_t::reset_pollin (handle_t handle_)
 #if defined ZMQ_HAVE_WINDOWS
     u_short family = get_fd_family (handle_);
     wsa_assert (family != AF_UNSPEC);
-    FD_CLR (handle_, &family_entries [family].fds_set.read);
-#else
-    FD_CLR (handle_, &fds_set.read);
+    family_entry_t &family_entry = family_entries [family];
 #endif
+    FD_CLR (handle_, &family_entry.fds_set.read);
 }
 
 void zmq::select_t::set_pollout (handle_t handle_)
@@ -197,10 +239,9 @@ void zmq::select_t::set_pollout (handle_t handle_)
 #if defined ZMQ_HAVE_WINDOWS
     u_short family = get_fd_family (handle_);
     wsa_assert (family != AF_UNSPEC);
-    FD_SET (handle_, &family_entries [family].fds_set.write);
-#else
-    FD_SET (handle_, &fds_set.write);
+    family_entry_t &family_entry = family_entries [family];
 #endif
+    FD_SET (handle_, &family_entry.fds_set.write);
 }
 
 void zmq::select_t::reset_pollout (handle_t handle_)
@@ -208,10 +249,9 @@ void zmq::select_t::reset_pollout (handle_t handle_)
 #if defined ZMQ_HAVE_WINDOWS
     u_short family = get_fd_family (handle_);
     wsa_assert (family != AF_UNSPEC);
-    FD_CLR (handle_, &family_entries [family].fds_set.write);
-#else
-    FD_CLR (handle_, &fds_set.write);
+    family_entry_t &family_entry = family_entries [family];
 #endif
+    FD_CLR (handle_, &family_entry.fds_set.write);
 }
 
 void zmq::select_t::start ()
@@ -236,9 +276,10 @@ void zmq::select_t::loop ()
         int timeout = (int) execute_timers ();
 
 #if defined ZMQ_HAVE_OSX
-        struct timeval tv = { (long) (timeout / 1000), timeout % 1000 * 1000 };
+        struct timeval tv = {(long) (timeout / 1000), timeout % 1000 * 1000};
 #else
-        struct timeval tv = { (long) (timeout / 1000), (long) (timeout % 1000 * 1000) };
+        struct timeval tv = {(long) (timeout / 1000),
+                             (long) (timeout % 1000 * 1000)};
 #endif
 
         int rc = 0;
@@ -253,38 +294,51 @@ void zmq::select_t::loop ()
             cannot be used alone, because it does not support more than 64 events
             which is not enough.
 
-            To reduce unncessary overhead, WSA is only used when there are more
+            To reduce unnecessary overhead, WSA is only used when there are more
             than one family. Moreover, AF_INET and AF_INET6 are considered the same
             family because Windows seems to handle them properly.
             See get_fd_family for details.
         */
 
         //  If there is just one family, there is no reason to use WSA events.
-        if (family_entries.size () > 1) {
+        const bool use_wsa_events = family_entries.size () > 1;
+        if (use_wsa_events) {
+            // TODO: I don't really understand why we are doing this. If any of
+            // the events was signaled, we will call select for each fd_family
+            // afterwards. The only benefit is if none of the events was
+            // signaled, then we continue early.
+            // IMHO, either WSAEventSelect/WSAWaitForMultipleEvents or select
+            // should be used, but not both
+
             wsa_events_t wsa_events;
 
-            for (family_entries_t::iterator family_entry_it = family_entries.begin ();
+            for (family_entries_t::iterator family_entry_it =
+                   family_entries.begin ();
                  family_entry_it != family_entries.end (); ++family_entry_it) {
-                family_entry_t& family_entry = family_entry_it->second;
+                family_entry_t &family_entry = family_entry_it->second;
 
-                for (fd_entries_t::iterator fd_entry_it = family_entry.fd_entries.begin ();
-                      fd_entry_it != family_entry.fd_entries.end (); ++fd_entry_it) {
+                for (fd_entries_t::iterator fd_entry_it =
+                       family_entry.fd_entries.begin ();
+                     fd_entry_it != family_entry.fd_entries.end ();
+                     ++fd_entry_it) {
                     fd_t fd = fd_entry_it->fd;
 
                     //  http://stackoverflow.com/q/35043420/188530
-                    if (FD_ISSET (fd, &family_entry.fds_set.read) &&
-                          FD_ISSET (fd, &family_entry.fds_set.write))
-                        rc = WSAEventSelect (fd, wsa_events.events [3],
-                            FD_READ | FD_ACCEPT | FD_CLOSE | FD_WRITE | FD_CONNECT | FD_OOB);
+                    if (FD_ISSET (fd, &family_entry.fds_set.read)
+                        && FD_ISSET (fd, &family_entry.fds_set.write))
+                        rc =
+                          WSAEventSelect (fd, wsa_events.events [3],
+                                          FD_READ | FD_ACCEPT | FD_CLOSE
+                                            | FD_WRITE | FD_CONNECT | FD_OOB);
                     else if (FD_ISSET (fd, &family_entry.fds_set.read))
                         rc = WSAEventSelect (fd, wsa_events.events [0],
-                            FD_READ | FD_ACCEPT | FD_CLOSE | FD_OOB);
+                                             FD_READ | FD_ACCEPT | FD_CLOSE
+                                               | FD_OOB);
                     else if (FD_ISSET (fd, &family_entry.fds_set.write))
                         rc = WSAEventSelect (fd, wsa_events.events [1],
                                              FD_WRITE | FD_CONNECT | FD_OOB);
                     else if (FD_ISSET (fd, &family_entry.fds_set.error))
-                        rc = WSAEventSelect (fd, wsa_events.events [2],
-                            FD_OOB);
+                        rc = WSAEventSelect (fd, wsa_events.events [2], FD_OOB);
                     else
                         rc = 0;
 
@@ -294,7 +348,7 @@ void zmq::select_t::loop ()
 
             rc = WSAWaitForMultipleEvents (4, wsa_events.events, FALSE,
                                            timeout ? timeout : INFINITE, FALSE);
-            wsa_assert (rc != (int)WSA_WAIT_FAILED);
+            wsa_assert (rc != (int) WSA_WAIT_FAILED);
             zmq_assert (rc != WSA_WAIT_IO_COMPLETION);
 
             if (rc == WSA_WAIT_TIMEOUT)
@@ -302,111 +356,63 @@ void zmq::select_t::loop ()
         }
 
         for (current_family_entry_it = family_entries.begin ();
-              current_family_entry_it != family_entries.end (); ++current_family_entry_it) {
-            family_entry_t& family_entry = current_family_entry_it->second;
-
-            //  select will fail when run with empty sets.
-            if (family_entry.fd_entries.empty ())
-                continue;
+             current_family_entry_it != family_entries.end ();
+             ++current_family_entry_it) {
+            family_entry_t &family_entry = current_family_entry_it->second;
 
-            fds_set_t local_fds_set = family_entry.fds_set;
 
-            if (family_entries.size () > 1) {
+            if (use_wsa_events) {
                 //  There is no reason to wait again after WSAWaitForMultipleEvents.
                 //  Simply collect what is ready.
-                struct timeval tv_nodelay = { 0, 0 };
-                rc = select (0, &local_fds_set.read, &local_fds_set.write, &local_fds_set.error,
-                    &tv_nodelay);
+                struct timeval tv_nodelay = {0, 0};
+                select_family_entry (family_entry, 0, true, tv_nodelay);
+            } else {
+                select_family_entry (family_entry, 0, timeout > 0, tv);
             }
-            else
-                rc = select (0, &local_fds_set.read, &local_fds_set.write,
-                    &local_fds_set.error, timeout > 0 ? &tv : NULL);
-
-            wsa_assert (rc != SOCKET_ERROR);
-
-            //  Size is cached to avoid iteration through recently added descriptors.
-            for (fd_entries_t::size_type i = 0, size = family_entry.fd_entries.size (); i < size && rc > 0; ++i) {
-
-                if (family_entry.fd_entries[i].fd == retired_fd)
-                    continue;
-
-                if (FD_ISSET(family_entry.fd_entries[i].fd, &local_fds_set.read)) {
-                    family_entry.fd_entries[i].events->in_event();
-                    --rc;
         }
-
-                if (family_entry.fd_entries[i].fd == retired_fd || rc == 0)
-                    continue;
-
-                if (FD_ISSET(family_entry.fd_entries[i].fd, &local_fds_set.write)) {
-                    family_entry.fd_entries[i].events->out_event();
-                    --rc;
+#else
+        select_family_entry (family_entry, maxfd, timeout > 0, tv);
+#endif
     }
+}
 
-                if (family_entry.fd_entries[i].fd == retired_fd || rc == 0)
-                    continue;
+void zmq::select_t::select_family_entry (family_entry_t &family_entry_,
+                                         const int max_fd_,
+                                         const bool use_timeout_,
+                                         struct timeval &tv_)
+{
+    //  select will fail when run with empty sets.
+    fd_entries_t &fd_entries = family_entry_.fd_entries;
+    if (fd_entries.empty ())
+        return;
 
-                if (FD_ISSET(family_entry.fd_entries[i].fd, &local_fds_set.error)) {
-                    family_entry.fd_entries[i].events->in_event();
-                    --rc;
-                }
-            }
+    fds_set_t local_fds_set = family_entry_.fds_set;
+    int rc = select (max_fd_, &local_fds_set.read, &local_fds_set.write,
+                     &local_fds_set.error, use_timeout_ ? &tv_ : NULL);
 
-            if (family_entry.retired) {
-                family_entry.retired = false;
-                family_entry.fd_entries.erase (std::remove_if (family_entry.fd_entries.begin (),
-                    family_entry.fd_entries.end (), is_retired_fd), family_entry.fd_entries.end ());
-            }
-        }
+#if defined ZMQ_HAVE_WINDOWS
+    wsa_assert (rc != SOCKET_ERROR);
 #else
-        fds_set_t local_fds_set = fds_set;
-        rc = select (maxfd + 1, &local_fds_set.read, &local_fds_set.write,
-            &local_fds_set.error, timeout ? &tv : NULL);
-
     if (rc == -1) {
         errno_assert (errno == EINTR);
-            continue;
+        return;
     }
+#endif
 
-        //  Size is cached to avoid iteration through just added descriptors.
-        for (fd_entries_t::size_type i = 0, size = fd_entries.size (); i < size && rc > 0; ++i) {
-            if (fd_entries [i].fd == retired_fd)
-                continue;
-
-            if (FD_ISSET (fd_entries [i].fd, &local_fds_set.read)) {
-                fd_entries [i].events->in_event ();
-                --rc;
-            }
-
-            if (fd_entries [i].fd == retired_fd || rc == 0)
-                continue;
-
-            if (FD_ISSET (fd_entries [i].fd, &local_fds_set.write)) {
-                fd_entries [i].events->out_event ();
-                --rc;
-            }
-
-            if (fd_entries [i].fd == retired_fd || rc == 0)
-                continue;
-
-            if (FD_ISSET (fd_entries [i].fd, &local_fds_set.error)) {
-                fd_entries [i].events->in_event ();
-                --rc;
-            }
-        }
+    trigger_events (fd_entries, local_fds_set, rc);
 
-        if (retired) {
-            retired = false;
-            fd_entries.erase (std::remove_if (fd_entries.begin (), fd_entries.end (),
-                is_retired_fd), fd_entries.end ());
-        }
-#endif
+    if (family_entry_.retired) {
+        family_entry_.retired = false;
+        family_entry_.fd_entries.erase (std::remove_if (fd_entries.begin (),
+                                                        fd_entries.end (),
+                                                        is_retired_fd),
+                                        family_entry_.fd_entries.end ());
     }
 }
 
 void zmq::select_t::worker_routine (void *arg_)
 {
-    ((select_t*) arg_)->loop ();
+    ((select_t *) arg_)->loop ();
 }
 
 zmq::select_t::fds_set_t::fds_set_t ()
@@ -416,16 +422,22 @@ zmq::select_t::fds_set_t::fds_set_t ()
     FD_ZERO (&error);
 }
 
-zmq::select_t::fds_set_t::fds_set_t (const fds_set_t& other_)
+zmq::select_t::fds_set_t::fds_set_t (const fds_set_t &other_)
 {
 #if defined ZMQ_HAVE_WINDOWS
     // On Windows we don't need to copy the whole fd_set.
     // SOCKETS are continuous from the beginning of fd_array in fd_set.
     // We just need to copy fd_count elements of fd_array.
     // We gain huge memcpy() improvement if number of used SOCKETs is much lower than FD_SETSIZE.
-    memcpy (&read,  &other_.read,  (char *) (other_.read.fd_array  + other_.read.fd_count ) - (char *) &other_.read );
-    memcpy (&write, &other_.write, (char *) (other_.write.fd_array + other_.write.fd_count) - (char *) &other_.write);
-    memcpy (&error, &other_.error, (char *) (other_.error.fd_array + other_.error.fd_count) - (char *) &other_.error);
+    memcpy (&read, &other_.read,
+            (char *) (other_.read.fd_array + other_.read.fd_count)
+              - (char *) &other_.read);
+    memcpy (&write, &other_.write,
+            (char *) (other_.write.fd_array + other_.write.fd_count)
+              - (char *) &other_.write);
+    memcpy (&error, &other_.error,
+            (char *) (other_.error.fd_array + other_.error.fd_count)
+              - (char *) &other_.error);
 #else
     memcpy (&read, &other_.read, sizeof other_.read);
     memcpy (&write, &other_.write, sizeof other_.write);
@@ -433,16 +445,23 @@ zmq::select_t::fds_set_t::fds_set_t (const fds_set_t& other_)
 #endif
 }
 
-zmq::select_t::fds_set_t& zmq::select_t::fds_set_t::operator= (const fds_set_t& other_)
+zmq::select_t::fds_set_t &zmq::select_t::fds_set_t::
+operator= (const fds_set_t &other_)
 {
 #if defined ZMQ_HAVE_WINDOWS
     // On Windows we don't need to copy the whole fd_set.
     // SOCKETS are continuous from the beginning of fd_array in fd_set.
     // We just need to copy fd_count elements of fd_array.
     // We gain huge memcpy() improvement if number of used SOCKETs is much lower than FD_SETSIZE.
-    memcpy (&read,  &other_.read,  (char *) (other_.read.fd_array  + other_.read.fd_count ) - (char *) &other_.read );
-    memcpy (&write, &other_.write, (char *) (other_.write.fd_array + other_.write.fd_count) - (char *) &other_.write);
-    memcpy (&error, &other_.error, (char *) (other_.error.fd_array + other_.error.fd_count) - (char *) &other_.error);
+    memcpy (&read, &other_.read,
+            (char *) (other_.read.fd_array + other_.read.fd_count)
+              - (char *) &other_.read);
+    memcpy (&write, &other_.write,
+            (char *) (other_.write.fd_array + other_.write.fd_count)
+              - (char *) &other_.write);
+    memcpy (&error, &other_.error,
+            (char *) (other_.error.fd_array + other_.error.fd_count)
+              - (char *) &other_.error);
 #else
     memcpy (&read, &other_.read, sizeof other_.read);
     memcpy (&write, &other_.write, sizeof other_.write);
@@ -451,7 +470,7 @@ zmq::select_t::fds_set_t& zmq::select_t::fds_set_t::operator= (const fds_set_t&
     return *this;
 }
 
-void zmq::select_t::fds_set_t::remove_fd (const fd_t& fd_)
+void zmq::select_t::fds_set_t::remove_fd (const fd_t &fd_)
 {
     FD_CLR (fd_, &read);
     FD_CLR (fd_, &write);
@@ -466,20 +485,48 @@ bool zmq::select_t::is_retired_fd (const fd_entry_t &entry)
 #if defined ZMQ_HAVE_WINDOWS
 u_short zmq::select_t::get_fd_family (fd_t fd_)
 {
-    //  Use sockaddr_storage instead of sockaddr to accomodate differect structure sizes
-    sockaddr_storage addr = { 0 };
+    // cache the results of determine_fd_family, as this is frequently called
+    // for the same sockets, and determine_fd_family is expensive
+    size_t i;
+    for (i = 0; i < fd_family_cache_size; ++i) {
+        const std::pair<fd_t, u_short> &entry = fd_family_cache [i];
+        if (entry.first == fd_) {
+            return entry.second;
+        }
+        if (entry.first == retired_fd)
+            break;
+    }
+
+    std::pair<fd_t, u_short> res =
+      std::make_pair (fd_, determine_fd_family (fd_));
+    if (i < fd_family_cache_size) {
+        fd_family_cache [i] = res;
+    } else {
+        // just overwrite a random entry
+        // could be optimized by some LRU strategy
+        fd_family_cache [rand () % fd_family_cache_size] = res;
+    }
+
+    return res.second;
+}
+
+u_short zmq::select_t::determine_fd_family (fd_t fd_)
+{
+    //  Use sockaddr_storage instead of sockaddr to accommodate different structure sizes
+    sockaddr_storage addr = {0};
     int addr_size = sizeof addr;
 
     int type;
-    int type_length = sizeof(int);
+    int type_length = sizeof (int);
 
-    int rc = getsockopt(fd_, SOL_SOCKET, SO_TYPE, (char*) &type, &type_length);
+    int rc =
+      getsockopt (fd_, SOL_SOCKET, SO_TYPE, (char *) &type, &type_length);
 
     if (rc == 0) {
         if (type == SOCK_DGRAM)
             return AF_INET;
         else {
-            rc = getsockname(fd_, (sockaddr *)&addr, &addr_size);
+            rc = getsockname (fd_, (sockaddr *) &addr, &addr_size);
 
             //  AF_INET and AF_INET6 can be mixed in select
             //  TODO: If proven otherwise, should simply return addr.sa_family
@@ -491,8 +538,7 @@ u_short zmq::select_t::get_fd_family (fd_t fd_)
     return AF_UNSPEC;
 }
 
-zmq::select_t::family_entry_t::family_entry_t () :
-    retired (false)
+zmq::select_t::family_entry_t::family_entry_t () : retired (false)
 {
 }
 

src/select.hpp

@@ -53,16 +53,14 @@
 
 namespace zmq
 {
+struct i_poll_events;
 
-    struct i_poll_events;
+//  Implements socket polling mechanism using POSIX.1-2001 select()
+//  function.
 
-    //  Implements socket polling mechanism using POSIX.1-2001 select()
-    //  function.
-
-    class select_t : public poller_base_t
-    {
+class select_t : public poller_base_t
+{
   public:
-
     typedef fd_t handle_t;
 
     select_t (const ctx_t &ctx_);
@@ -81,7 +79,6 @@ namespace zmq
     static int max_fds ();
 
   private:
-
     //  Main worker thread routine.
     static void worker_routine (void *arg_);
 
@@ -95,10 +92,10 @@ namespace zmq
     struct fds_set_t
     {
         fds_set_t ();
-            fds_set_t (const fds_set_t& other_);
-            fds_set_t& operator=(const fds_set_t& other_);
-            //  Convinient method to descriptor from all sets.
-            void remove_fd (const fd_t& fd_);
+        fds_set_t (const fds_set_t &other_);
+        fds_set_t &operator= (const fds_set_t &other_);
+        //  Convenience method to descriptor from all sets.
+        void remove_fd (const fd_t &fd_);
 
         fd_set read;
         fd_set write;
@@ -108,11 +105,14 @@ namespace zmq
     struct fd_entry_t
     {
         fd_t fd;
-            zmq::i_poll_events* events;
+        zmq::i_poll_events *events;
     };
     typedef std::vector<fd_entry_t> fd_entries_t;
 
-#if defined ZMQ_HAVE_WINDOWS
+    void trigger_events (const fd_entries_t &fd_entries_,
+                         const fds_set_t &local_fds_set_,
+                         int event_count_);
+
     struct family_entry_t
     {
         family_entry_t ();
@@ -121,6 +121,13 @@ namespace zmq
         fds_set_t fds_set;
         bool retired;
     };
+
+    void select_family_entry (family_entry_t &family_entry_,
+                              int max_fd_,
+                              bool use_timeout_,
+                              struct timeval &tv_);
+
+#if defined ZMQ_HAVE_WINDOWS
     typedef std::map<u_short, family_entry_t> family_entries_t;
 
     struct wsa_events_t
@@ -131,26 +138,28 @@ namespace zmq
         //  read, write, error and readwrite
         WSAEVENT events [4];
     };
-#endif
 
-#if defined ZMQ_HAVE_WINDOWS
     family_entries_t family_entries;
     // See loop for details.
     family_entries_t::iterator current_family_entry_it;
 
     bool try_remove_fd_entry (family_entries_t::iterator family_entry_it,
                               zmq::fd_t &handle_);
+
+    static const size_t fd_family_cache_size = 8;
+    std::pair<fd_t, u_short> fd_family_cache [fd_family_cache_size];
+
+    u_short get_fd_family (fd_t fd_);
+
+    //  Socket's family or AF_UNSPEC on error.
+    static u_short determine_fd_family (fd_t fd_);
 #else
-        fd_entries_t fd_entries;
-        fds_set_t fds_set;
+    //  on non-Windows, we can treat all fds as one family
+    family_entry_t family_entry;
     fd_t maxfd;
     bool retired;
 #endif
 
-#if defined ZMQ_HAVE_WINDOWS
-        //  Socket's family or AF_UNSPEC on error.
-        static u_short get_fd_family (fd_t fd_);
-#endif
     //  Checks if an fd_entry_t is retired.
     static bool is_retired_fd (const fd_entry_t &entry);
 
@@ -163,12 +172,11 @@ namespace zmq
     //  Handle of the physical thread doing the I/O work.
     thread_t worker;
 
-        select_t (const select_t&);
-        const select_t &operator = (const select_t&);
-    };
-
-    typedef select_t poller_t;
+    select_t (const select_t &);
+    const select_t &operator= (const select_t &);
+};
 
+typedef select_t poller_t;
 }
 
 #endif