+
+class PersistentFileHelperCtxMgr(object):
+ """A context manager for Python's "with" statement, which ensures that any
+ generated file is deleted (and hence regenerated) if its mtime is older
+ than the mtime of the Python module which generated it, and gets an mtime
+ newer than the mtime of the Python module which generated after it is
+ generated. Objects of this type should be created by factory function
+ persistent_file_helper rather than directly."""
+
+ def __init__(self, log, filename):
+ """Initialize a new object.
+
+ Args:
+ log: The Logfile object to log to.
+ filename: The filename of the generated file.
+
+ Returns:
+ Nothing.
+ """
+
+ self.log = log
+ self.filename = filename
+
+ def __enter__(self):
+ frame = inspect.stack()[1]
+ module = inspect.getmodule(frame[0])
+ self.module_filename = module.__file__
+ self.module_timestamp = os.path.getmtime(self.module_filename)
+
+ if os.path.exists(self.filename):
+ filename_timestamp = os.path.getmtime(self.filename)
+ if filename_timestamp < self.module_timestamp:
+ self.log.action('Removing stale generated file ' +
+ self.filename)
+ os.unlink(self.filename)
+
+ def __exit__(self, extype, value, traceback):
+ if extype:
+ try:
+ os.path.unlink(self.filename)
+ except:
+ pass
+ return
+ logged = False
+ for i in range(20):
+ filename_timestamp = os.path.getmtime(self.filename)
+ if filename_timestamp > self.module_timestamp:
+ break
+ if not logged:
+ self.log.action(
+ 'Waiting for generated file timestamp to increase')
+ logged = True
+ os.utime(self.filename)
+ time.sleep(0.1)
+
+def persistent_file_helper(u_boot_log, filename):
+ """Manage the timestamps and regeneration of a persistent generated
+ file. This function creates a context manager for Python's "with"
+ statement
+
+ Usage:
+ with persistent_file_helper(u_boot_console.log, filename):
+ code to generate the file, if it's missing.
+
+ Args:
+ u_boot_log: u_boot_console.log.
+ filename: The filename of the generated file.
+
+ Returns:
+ A context manager object.
+ """
+
+ return PersistentFileHelperCtxMgr(u_boot_log, filename)