Add a mode to ensure a server is not already running.

tools/xdisplaycheck/xdisplaycheck.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This is a small program that tries to connect to the X server.  It
 // continually retries until it connects or 30 seconds pass.  If it fails
 // to connect to the X server or fails to find needed functiona, it returns
 // an error code of -1.
 //
 // This is to help verify that a useful X server is available before we start
 // start running tests on the build bots.
 
 #include <errno.h>
 #include <stdio.h>
+#include <string.h>
 #include <time.h>
 #include <X11/Xlib.h>
 
 #if defined(USE_AURA)
 #include <X11/extensions/XInput2.h>
 #endif
 
 void Sleep(int duration_ms) {
   struct timespec sleep_time, remaining;
 
   // Contains the portion of duration_ms >= 1 sec.
   sleep_time.tv_sec = duration_ms / 1000;
   duration_ms -= sleep_time.tv_sec * 1000;
 
   // Contains the portion of duration_ms < 1 sec.
   sleep_time.tv_nsec = duration_ms * 1000 * 1000;  // nanoseconds.
 
   while (nanosleep(&sleep_time, &remaining) == -1 && errno == EINTR)
     sleep_time = remaining;
 }
 
 int main(int argc, char* argv[]) {
+  Display* display = NULL;
+  if (argv[1] && strcmp(argv[1], "--noserver")==0) {

[cmp, 2012/05/18 20:05:24]

spaces around ==

[Peter Mayo, 2012/05/18 20:25:44]

Done.

+    display = XOpenDisplay(NULL);
+    if (display) {
+      fprintf(stderr, "Found unexpected connectable display %s\n",
+              XDisplayName(NULL));
+    }
+    // Use upside down logic to resemble previous behaviour.

[cmp, 2012/05/18 20:05:24]

can you change this comment to be more explicit about the case you're returning
on?  (for example 'previous behavior' won't be clear later to others looking at
the code, 'upside down logic' is not clear to me.)

[Peter Mayo, 2012/05/18 20:25:44]

Better?

+    return !display;
+  }
+
   int kNumTries = 78;  // 78*77/2 * 10 = 30s of waiting
-  Display* display = NULL;
   int tries;
   for (tries = 0; tries < kNumTries; ++tries) {
     display = XOpenDisplay(NULL);
     if (display)
       break;
     Sleep(10 * tries);
   }
 
   if (!display) {
     fprintf(stderr, "Failed to connect to %s\n", XDisplayName(NULL));
@@ skipping 23 matching lines @@
   XIDeviceInfo* devices = XIQueryDevice(display, XIAllDevices, &count);
   if (devices)
     XIFreeDeviceInfo(devices);
 
   fprintf(stderr,
       "XInput2 verified initially sane on %s.\n", XDisplayName(NULL));
 #endif
 
   return 0;
 }