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 holding__threading_local = False
  22
  23 try:
  24     # Could have checked if ``thread`` was not in sys.modules and gone
  25     # a different route, but decided to mirror technique used with
  26     # ``threading`` below.
  27     if 'thread' in sys_modules:
  28         held_thread = sys_modules['thread']
  29         holding_thread = True
  30     # Must have some module named ``thread`` that implements its API
  31     # in order to initially import ``threading``.
  32     sys_modules['thread'] = sys_modules['dummy_thread']
  33
  34     if 'threading' in sys_modules:
  35         # If ``threading`` is already imported, might as well prevent
  36         # trying to import it more than needed by saving it if it is
  37         # already imported before deleting it.
  38         held_threading = sys_modules['threading']
  39         holding_threading = True
  40         del sys_modules['threading']
  41
  42     if '_threading_local' in sys_modules:
  43         # If ``_threading_local`` is already imported, might as well prevent
  44         # trying to import it more than needed by saving it if it is
  45         # already imported before deleting it.
  46         held__threading_local = sys_modules['_threading_local']
  47         holding__threading_local = True
  48         del sys_modules['_threading_local']
  49
  50     import threading
  51     # Need a copy of the code kept somewhere...
  52     sys_modules['_dummy_threading'] = sys_modules['threading']
  53     del sys_modules['threading']
  54     sys_modules['_dummy__threading_local'] = sys_modules['_threading_local']
  55     del sys_modules['_threading_local']
  56     from _dummy_threading import *
  57     from _dummy_threading import __all__
  58
  59 finally:
  60     # Put back ``threading`` if we overwrote earlier
  61
  62     if holding_threading:
  63         sys_modules['threading'] = held_threading
  64         del held_threading
  65     del holding_threading
  66
  67     # Put back ``_threading_local`` if we overwrote earlier
  68
  69     if holding__threading_local:
  70         sys_modules['_threading_local'] = held__threading_local
  71         del held__threading_local
  72     del holding__threading_local
  73
  74     # Put back ``thread`` if we overwrote, else del the entry we made
  75     if holding_thread:
  76         sys_modules['thread'] = held_thread
  77         del held_thread
  78     else:
  79         del sys_modules['thread']
  80     del holding_thread
  81
  82     del dummy_thread
  83     del sys_modules