Avoid problems when multiple processes generate the same file (fixes m…

…hammond#1600)

com/win32com/client/genpy.py

@@ -769,24 +769,49 @@ def BuildOleItemsFromType(self):
  def open_writer(self, filename, encoding="mbcs"):
  # A place to put code to open a file with the appropriate encoding.
  # Does *not* set self.file - just opens and returns a file.
- # Actually *deletes* the filename asked for and returns a handle to a
- # temp file - finish_writer then puts everything back in place. This
+ # Actually returns a handle to a temp file - finish_writer then deletes
+ # the filename asked for and puts everything back in place. This
  # is so errors don't leave a 1/2 generated file around causing bizarre
- # errors later.
+ # errors later, and so that multiple processes writing the same file
+ # don't step on each others' toes.
  # Could be a classmethod one day...
+ temp_filename = self.get_temp_filename(filename)
+ return open(temp_filename, "wt", encoding=encoding)
+
+ def finish_writer(self, filename, f, worked):
+ f.close()
  try:
  os.unlink(filename)
  except os.error:
  pass
- filename = filename + ".temp"
- return open(filename, "wt", encoding=encoding)
-
- def finish_writer(self, filename, f, worked):
- f.close()
+ temp_filename = self.get_temp_filename(filename)
  if worked:
- os.rename(filename + ".temp", filename)
+ try:
+ os.rename(temp_filename, filename)
+ except os.error:
+ # If we are really unlucky, another process may have written the
+ # file in between our calls to os.unlink and os.rename. So try
+ # again, but only once.
+ # There are still some race conditions, but they seem difficult to
+ # fix, and they probably occur much less frequently:
+ # * The os.rename failure could occur more than once if more than
+ # two processes are involved.
+ # * In between os.unlink and os.rename, another process could try
+ # to import the module, having seen that it already exists.
+ # * If another process starts a COM server while we are still
+ # generating __init__.py, that process sees that the folder
+ # already exists and assumes that __init__.py is already there
+ # as well.
+ try:
+ os.unlink(filename)
+ except os.error:
+ pass
+ os.rename(temp_filename, filename)
  else:
- os.unlink(filename + ".temp")
+ os.unlink(temp_filename)
+
+ def get_temp_filename(self, filename):
+ return '%s.%d.temp' % (filename, os.getpid())
 
  def generate(self, file, is_for_demand = 0):
  if is_for_demand: