blob: 1bb7eee338af2458ce35a55dc946d2057f9a5d80 [file] [log] [blame]
Antoine Pitroub43c4ca2017-09-18 22:04:20 +02001"""Faux ``threading`` version using ``dummy_thread`` instead of ``thread``.
2
3The module ``_dummy_threading`` is added to ``sys.modules`` in order
4to not have ``threading`` considered imported. Had ``threading`` been
5directly imported it would have made all subsequent imports succeed
6regardless of whether ``_thread`` was available which is not desired.
7
8"""
9from sys import modules as sys_modules
10
11import _dummy_thread
12
13# Declaring now so as to not have to nest ``try``s to get proper clean-up.
14holding_thread = False
15holding_threading = False
16holding__threading_local = False
17
18try:
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
54finally:
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