webkitpy: Check xvfb with xdpyinfo after starting.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 30 matching lines @@
 
     SUPPORTED_VERSIONS = ('trusty',)
 
     FALLBACK_PATHS = {}
     FALLBACK_PATHS['trusty'] = ['linux'] + win.WinPort.latest_platform_fallback_path()
 
     DEFAULT_BUILD_DIRECTORIES = ('out',)
 
     BUILD_REQUIREMENTS_URL = 'https://chromium.googlesource.com/chromium/src/+/master/docs/linux_build_instructions.md'
 
+    XVFB_START_TIMEOUT = 5.0  # Wait up to 5 seconds for Xvfb to start.
+
     @classmethod
     def determine_full_port_name(cls, host, options, port_name):
         if port_name.endswith('linux'):
             assert host.platform.is_linux()
             version = host.platform.os_version
             return port_name + '-' + version
         return port_name
 
     def __init__(self, host, port_name, **kwargs):
         super(LinuxPort, self).__init__(host, port_name, **kwargs)
@@ skipping 100 matching lines @@
         # get the right DISPLAY. Note, if this environment could be passed
         # when creating workers, then we wouldn't need to modify DISPLAY here.
         self._original_display = self.host.environ.get('DISPLAY')
         self.host.environ['DISPLAY'] = display
 
         # The poll() method will return None if the process has not terminated:
         # https://docs.python.org/2/library/subprocess.html#subprocess.Popen.poll
         if self._xvfb_process.poll() is not None:
             _log.warn('Failed to start Xvfb on display "%s."', display)
 
+        start_time = self.host.time()
+        while self.host.time() - start_time < self.XVFB_START_TIMEOUT:
+            # We don't explicitly set the display, as we want to check the
+            # environment value.
+            exit_code = self.host.executive.run_command(
+                ['xdpyinfo'], return_exit_code=True)
+            if exit_code == 0:
+                _log.info('Successfully started Xvfb with display "%s".', display)
+                return
+            _log.warn('xdpyinfo check failed with exit code %s while starting Xvfb on "%s".', exit_code, display)
+            self.host.sleep(0.1)
+        _log.fatal('Failed to start Xvfb on display "%s" (xdpyinfo check failed).', display)
+
     def _find_display(self):
         """Tries to find a free X display, looping if necessary."""
         # The "xvfb-run" command uses :99 by default.
         for display_number in range(99, 120):
             display = ':%d' % display_number
             exit_code = self.host.executive.run_command(
                 ['xdpyinfo', '-display', display], return_exit_code=True)
             if exit_code == 1:
                 return display
         return None
 
     def _stop_xvfb(self):
         if self._original_display:
             self.host.environ['DISPLAY'] = self._original_display
         if not self._xvfb_process:
             return
         _log.debug('Killing Xvfb process pid %d.', self._xvfb_process.pid)
         self._xvfb_process.kill()
         self._xvfb_process.wait()
 
 
     def _path_to_driver(self, target=None):
         binary_name = self.driver_name()
         return self._build_path_with_target(target, binary_name)