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 """
   9 from sys import modules as sys_modules
  10
  11 import dummy_thread
  12
  13 # Declaring now so as to not have to nest ``try``s to get proper clean-up.
  14 holding_thread = False
  15 holding_threading = False
  16 holding__threading_local = False
  17
  18 try:
  19     # Could have checked if ``thread`` was not in sys.modules and gone
  20     # a different route, but decided to mirror technique used with
  21     # ``threading`` below.
  22     if 'thread' in sys_modules:
  23         held_thread = sys_modules['thread']
  24         holding_thread = True
  25     # Must have some module named ``thread`` that implements its API
  26     # in order to initially import ``threading``.
  27     sys_modules['thread'] = sys_modules['dummy_thread']
  28
  29     if 'threading' in sys_modules:
  30         # If ``threading`` is already imported, might as well prevent
  31         # trying to import it more than needed by saving it if it is
  32         # already imported before deleting it.
  33         held_threading = sys_modules['threading']
  34         holding_threading = True
  35         del sys_modules['threading']
  36
  37     if '_threading_local' in sys_modules:
  38         # If ``_threading_local`` is already imported, might as well prevent
  39         # trying to import it more than needed by saving it if it is
  40         # already imported before deleting it.
  41         held__threading_local = sys_modules['_threading_local']
  42         holding__threading_local = True
  43         del sys_modules['_threading_local']
  44
  45     import threading
  46     # Need a copy of the code kept somewhere...
  47     sys_modules['_dummy_threading'] = sys_modules['threading']
  48     del sys_modules['threading']
  49     sys_modules['_dummy__threading_local'] = sys_modules['_threading_local']
  50     del sys_modules['_threading_local']
  51     from _dummy_threading import *
  52     from _dummy_threading import __all__
  53
  54 finally:
  55     # Put back ``threading`` if we overwrote earlier
  56
  57     if holding_threading:
  58         sys_modules['threading'] = held_threading
  59         del held_threading
  60     del holding_threading
  61
  62     # Put back ``_threading_local`` if we overwrote earlier
  63
  64     if holding__threading_local:
  65         sys_modules['_threading_local'] = held__threading_local
  66         del held__threading_local
  67     del holding__threading_local
  68
  69     # Put back ``thread`` if we overwrote, else del the entry we made
  70     if holding_thread:
  71         sys_modules['thread'] = held_thread
  72         del held_thread
  73     else:
  74         del sys_modules['thread']
  75     del holding_thread
  76
  77     del dummy_thread
  78     del sys_modules