code: def cross_check_launchers(self, launchers):
          
          if len(launchers) == 0: raise Exception('Empty launcher list')
          timestamps = [launcher.timestamp for launcher in launchers]
  
          if not all(timestamps[0] == tstamp for tstamp in timestamps):
              raise Exception("Launcher timestamps not all equal. "
                              "Consider setting timestamp explicitly.")
  
          root_directories = []
          for launcher in launchers:
              command = launcher.command
              args = launcher.args
              command.verify(args)
              root_directory = launcher.get_root_directory()
              if os.path.isdir(root_directory):
                  raise Exception("Root directory already exists: %r" % root_directory)
              if root_directory in root_directories:
                  raise Exception("Each launcher requires a unique root directory")
              root_directories.append(root_directory)
docs: Performs consistency checks across all the launchers.