Improve tracing of xvfb.py

testing/xvfb.py

 #!/usr/bin/env python
 # 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.
 
 """Runs the test with xvfb on linux. Runs the test normally on other platforms.
 
 For simplicity in gyp targets, this script just runs the test normal on
 non-linux platforms.
 """
@@ skipping 37 matching lines @@
 
   Args:
     xvfb_path: Path to Xvfb.
   """
   cmd = [xvfb_path, display, '-screen', '0', '1024x768x24', '-ac']
   try:
     proc = subprocess.Popen(
         cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
   except OSError:
     print >> sys.stderr, 'Failed to run %s' % ' '.join(cmd)
-    return 0
-  return proc.pid
+    return
+  return proc
 
 
 def wait_for_xvfb(xdisplaycheck, env):
   """Waits for xvfb to be fully initialized by using xdisplaycheck."""
   try:
-    subprocess.check_call(
+    _logs = subprocess.check_output(
         [xdisplaycheck],
-        stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT,
         env=env)
   except OSError:
     print >> sys.stderr, 'Failed to load %s with cwd=%s' % (
         xdisplaycheck, os.getcwd())
     return False
-  except subprocess.CalledProcessError:
+  except subprocess.CalledProcessError as e:
     print >> sys.stderr, (
-        'Xvfb failed to load properly while trying to run %s' % xdisplaycheck)
+        'Xvfb failed to load properly (code %d) according to %s' %
+        (e.returncode, xdisplaycheck))
     return False
+
   return True
 
 
 def run_executable(cmd, build_dir, env):
   """Runs an executable within a xvfb buffer on linux or normally on other
   platforms.
 
   Requires that both xvfb and openbox are installed on linux.
 
   Detects recursion with an environment variable and do not create a recursive X
   buffer if present.
   """
   # First look if we are inside a display.
   if env.get('_CHROMIUM_INSIDE_XVFB') == '1':
     # No need to recurse.
     return test_env.run_executable(cmd, env)
 
   pid = None
   xvfb = 'Xvfb'
   try:
     if sys.platform == 'linux2':
       # Defaults to X display 9.
       display = ':9'
-      pid = start_xvfb(xvfb, display)
-      if not pid:
+      xvfb_proc = start_xvfb(xvfb, display)
+      if not xvfb_proc or not xvfb_proc.pid:
         return 1
       env['DISPLAY'] = display
       if not wait_for_xvfb(os.path.join(build_dir, 'xdisplaycheck'), env):
+        rc = xvfb_proc.poll()
+        if rc is None:
+          print 'Xvfb still running, stopping.'
+          xvfb_proc.terminate()
+        else:
+          print 'Xvfb exited, code %d' % rc
+
+        print 'Xvfb output:'
+        for l in xvfb_proc.communicate()[0].splitlines():
+          print '> %s' % l
+
         return 3
       # Inhibit recursion.
       env['_CHROMIUM_INSIDE_XVFB'] = '1'
       # Some ChromeOS tests need a window manager. Technically, it could be
       # another script but that would be overkill.
       try:
         wm_cmd = ['openbox']
         subprocess.Popen(
             wm_cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, env=env)
       except OSError:
         print >> sys.stderr, 'Failed to run %s' % ' '.join(wm_cmd)
         return 1
     return test_env.run_executable(cmd, env)
   finally:
     if pid:
       kill(pid)
 
 
 def main():
   if len(sys.argv) < 3:
     print >> sys.stderr, (
         'Usage: xvfb.py [path to build_dir] [command args...]')
     return 2
   return run_executable(sys.argv[2:], sys.argv[1], os.environ.copy())
 
 
 if __name__ == "__main__":
   sys.exit(main())