Lib/dummy_threading.py

   1 """Faux ``threading`` version using ``dummy_thread`` instead of ``thread``.
   2
   3 The module ``_dummy_threading`` is added to ``sys.modules`` in order
   4 to not have ``threading`` considered imported.  Had ``threading`` been
   5 directly imported it would have made all subsequent imports succeed
   6 regardless of whether ``thread`` was available which is not desired.
   7
   8 :Author: Brett Cannon
   9 :Contact: brett@python.org
  10
  11 XXX: Try to get rid of ``_dummy_threading``.
  12
  13 """
  14 from sys import modules as sys_modules
  15
  16 import dummy_thread
  17
  18 # Declaring now so as to not have to nest ``try``s to get proper clean-up.
  19 holding_thread = False
  20 holding_threading = False
  21
  22 try:
  23     # Could have checked if ``thread`` was not in sys.modules and gone
  24     # a different route, but decided to mirror technique used with
  25     # ``threading`` below.
  26     if 'thread' in sys_modules:
  27         held_thread = sys_modules['thread']
  28         holding_thread = True
  29     # Must have some module named ``thread`` that implements its API
  30     # in order to initially import ``threading``.
  31     sys_modules['thread'] = sys_modules['dummy_thread']
  32
  33     if 'threading' in sys_modules:
  34         # If ``threading`` is already imported, might as well prevent
  35         # trying to import it more than needed by saving it if it is
  36         # already imported before deleting it.
  37         held_threading = sys_modules['threading']
  38         holding_threading = True
  39         del sys_modules['threading']
  40     import threading
  41     # Need a copy of the code kept somewhere...
  42     sys_modules['_dummy_threading'] = sys_modules['threading']
  43     del sys_modules['threading']
  44     from _dummy_threading import *
  45     from _dummy_threading import __all__
  46
  47 finally:
  48     # Put back ``threading`` if we overwrote earlier
  49     if holding_threading:
  50         sys_modules['threading'] = held_threading
  51         del held_threading
  52     del holding_threading
  53
  54     # Put back ``thread`` if we overwrote, else del the entry we made
  55     if holding_thread:
  56         sys_modules['thread'] = held_thread
  57         del held_thread
  58     else:
  59         del sys_modules['thread']
  60     del holding_thread
  61
  62     del dummy_thread
  63     del sys_modules