Use xcb for -queryExt instead of a round-trip per extension

On a system with 30 extensions listed by xdpyinfo, truss -c
reports this saves quite a few system calls by batching the
QueryExtension requests instead of a round-trip for each one:

                      Xlib      xcb
writev                  40       11
poll                    80       22
recv                   117       29
total (*)              464      296

(*) total includes all system calls, including many not shown since
their count did not change significantly.   There was one additional
set of open/mmap/close etc. for loading the added libX11-xcb library.

Over a tcp connection, this reduced both the number of packets,
and due to tcp packet header overhead, the overall amount of data:

                      Xlib      xcb
TCP packets             93       35
TCP bytes            11554     7726

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Jamey Sharp <jamey@minilop.net>

2 files changed, 45 insertions, 13 deletions

diff --git a/configure.ac b/configure.ac
index 48ae434..47a1246 100644
--- a/configure.ac
+++ b/configure.ac
@@ -36,7 +36,7 @@ XORG_DEFAULT_OPTIONS
 AM_CONFIG_HEADER(config.h)
 
 # Checks for pkg-config packages
-PKG_CHECK_MODULES(XDPYINFO, xext x11 xtst)
+PKG_CHECK_MODULES(XDPYINFO, xext x11 xtst x11-xcb xcb)
 
 # This is used below to allow <X11/Xlib.h> to be found
 PKG_CHECK_MODULES(DPY_X11, x11)
diff --git a/xdpyinfo.c b/xdpyinfo.c
index db4a438..017738f 100644
--- a/xdpyinfo.c
+++ b/xdpyinfo.c
@@ -82,6 +82,7 @@ in this Software without prior written authorization from The Open Group.
 
 #endif
 
+#include <X11/Xlib-xcb.h>
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #ifdef MULTIBUFFER
@@ -170,22 +171,53 @@ print_extension_info(Display *dpy)
     printf ("number of extensions:    %d\n", n);
 
     if (extlist) {
-        register int i;
-        int opcode, event, error;
+        int i;
 
         qsort(extlist, n, sizeof(char *), StrCmp);
-        for (i = 0; i < n; i++) {
-            if (!queryExtensions) {
+
+        if (!queryExtensions) {
+            for (i = 0; i < n; i++) {
                 printf ("    %s\n", extlist[i]);
-                continue;
             }
-            XQueryExtension(dpy, extlist[i], &opcode, &event, &error);
-            printf ("    %s  (opcode: %d", extlist[i], opcode);
-            if (event)
-                printf (", base event: %d", event);
-            if (error)
-                printf (", base error: %d", error);
-            printf(")\n");
+        } else {
+            xcb_connection_t *xcb_conn = XGetXCBConnection (dpy);
+            xcb_query_extension_cookie_t *qe_cookies;
+
+            qe_cookies = calloc(n, sizeof(xcb_query_extension_cookie_t));
+            if (!qe_cookies) {
+                perror ("calloc failed to allocate memory for extensions");
+                return;
+            }
+
+            /*
+             * Generate all extension queries at once, so they can be
+             * sent to the xserver in a single batch
+             */
+            for (i = 0; i < n; i++) {
+                qe_cookies[i] = xcb_query_extension (xcb_conn,
+                                                     strlen(extlist[i]),
+                                                     extlist[i]);
+            }
+
+            /*
+             * Start processing replies as they come in.
+             * The first call will flush the queue to the server, then
+             * each one will wait, if needed, for its reply.
+             */
+            for (i = 0; i < n; i++) {
+                xcb_query_extension_reply_t *rep
+                    = xcb_query_extension_reply(xcb_conn, qe_cookies[i], NULL);
+
+                printf ("    %s  (opcode: %d", extlist[i], rep->major_opcode);
+                if (rep->first_event)
+                    printf (", base event: %d", rep->first_event);
+                if (rep->first_error)
+                    printf (", base error: %d", rep->first_error);
+                printf (")\n");
+
+                free (rep);
+            }
+            free (qe_cookies);
         }
         /* do not free, Xlib can depend on contents being unaltered */
         /* XFreeExtensionList (extlist); */