vnc: threaded VNC server

Implement a threaded VNC server using the producer-consumer model.
The main thread will push encoding jobs (a list a rectangles to update)
in a queue, and the VNC worker thread will consume that queue and send
framebuffer updates to the output buffer.

The threaded VNC server can be enabled with ./configure --enable-vnc-thread.

If you don't want it, just use ./configure --disable-vnc-thread and a syncrhonous
queue of job will be used (which as exactly the same behavior as the old queue).
If you disable the VNC thread, all thread related code will not be built and there will
be no overhead.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/configure b/configure
index 59e9385..f5f7248 100755
--- a/configure
+++ b/configure
@@ -270,6 +270,7 @@
 vnc_sasl=""
 vnc_jpeg=""
 vnc_png=""
+vnc_thread=""
 xen=""
 linux_aio=""
 attr=""
@@ -585,6 +586,10 @@
   ;;
   --enable-vnc-png) vnc_png="yes"
   ;;
+  --disable-vnc-thread) vnc_thread="no"
+  ;;
+  --enable-vnc-thread) vnc_thread="yes"
+  ;;
   --disable-slirp) slirp="no"
   ;;
   --disable-uuid) uuid="no"
@@ -839,6 +844,8 @@
 echo "  --enable-vnc-jpeg        enable JPEG lossy compression for VNC server"
 echo "  --disable-vnc-png        disable PNG compression for VNC server"
 echo "  --enable-vnc-png         enable PNG compression for VNC server"
+echo "  --disable-vnc-thread     disable threaded VNC server"
+echo "  --enable-vnc-thread      enable threaded VNC server"
 echo "  --disable-curses         disable curses output"
 echo "  --enable-curses          enable curses output"
 echo "  --disable-curl           disable curl connectivity"
@@ -2156,6 +2163,7 @@
 echo "VNC SASL support  $vnc_sasl"
 echo "VNC JPEG support  $vnc_jpeg"
 echo "VNC PNG support   $vnc_png"
+echo "VNC thread        $vnc_thread"
 if test -n "$sparc_cpu"; then
     echo "Target Sparc Arch $sparc_cpu"
 fi
@@ -2301,6 +2309,10 @@
   echo "CONFIG_VNC_PNG=y" >> $config_host_mak
   echo "VNC_PNG_CFLAGS=$vnc_png_cflags" >> $config_host_mak
 fi
+if test "$vnc_thread" = "yes" ; then
+  echo "CONFIG_VNC_THREAD=y" >> $config_host_mak
+  echo "CONFIG_THREAD=y" >> $config_host_mak
+fi
 if test "$fnmatch" = "yes" ; then
   echo "CONFIG_FNMATCH=y" >> $config_host_mak
 fi
@@ -2377,6 +2389,7 @@
 fi
 if test "$io_thread" = "yes" ; then
   echo "CONFIG_IOTHREAD=y" >> $config_host_mak
+  echo "CONFIG_THREAD=y" >> $config_host_mak
 fi
 if test "$linux_aio" = "yes" ; then
   echo "CONFIG_LINUX_AIO=y" >> $config_host_mak