Python code coverage for Lib/test/test_threaded_import.py

#	count	content
1	n/a	# This is a variant of the very old (early 90's) file
2	n/a	# Demo/threads/bug.py. It simply provokes a number of threads into
3	n/a	# trying to import the same module "at the same time".
4	n/a	# There are no pleasant failure modes -- most likely is that Python
5	n/a	# complains several times about module random having no attribute
6	n/a	# randrange, and then Python hangs.
7	n/a
8	n/a	import _imp as imp
9	n/a	import os
10	n/a	import importlib
11	n/a	import sys
12	n/a	import time
13	n/a	import shutil
14	n/a	import unittest
15	n/a	from test.support import (
16	n/a	verbose, import_module, run_unittest, TESTFN, reap_threads,
17	n/a	forget, unlink, rmtree, start_threads)
18	n/a	threading = import_module('threading')
19	n/a
20	n/a	def task(N, done, done_tasks, errors):
21	n/a	try:
22	n/a	# We don't use modulefinder but still import it in order to stress
23	n/a	# importing of different modules from several threads.
24	n/a	if len(done_tasks) % 2:
25	n/a	import modulefinder
26	n/a	import random
27	n/a	else:
28	n/a	import random
29	n/a	import modulefinder
30	n/a	# This will fail if random is not completely initialized
31	n/a	x = random.randrange(1, 3)
32	n/a	except Exception as e:
33	n/a	errors.append(e.with_traceback(None))
34	n/a	finally:
35	n/a	done_tasks.append(threading.get_ident())
36	n/a	finished = len(done_tasks) == N
37	n/a	if finished:
38	n/a	done.set()
39	n/a
40	n/a	# Create a circular import structure: A -> C -> B -> D -> A
41	n/a	# NOTE: `time` is already loaded and therefore doesn't threaten to deadlock.
42	n/a
43	n/a	circular_imports_modules = {
44	n/a	'A': """if 1:
45	n/a	import time
46	n/a	time.sleep(%(delay)s)
47	n/a	x = 'a'
48	n/a	import C
49	n/a	""",
50	n/a	'B': """if 1:
51	n/a	import time
52	n/a	time.sleep(%(delay)s)
53	n/a	x = 'b'
54	n/a	import D
55	n/a	""",
56	n/a	'C': """import B""",
57	n/a	'D': """import A""",
58	n/a	}
59	n/a
60	n/a	class Finder:
61	n/a	"""A dummy finder to detect concurrent access to its find_spec()
62	n/a	method."""
63	n/a
64	n/a	def __init__(self):
65	n/a	self.numcalls = 0
66	n/a	self.x = 0
67	n/a	self.lock = threading.Lock()
68	n/a
69	n/a	def find_spec(self, name, path=None, target=None):
70	n/a	# Simulate some thread-unsafe behaviour. If calls to find_spec()
71	n/a	# are properly serialized, `x` will end up the same as `numcalls`.
72	n/a	# Otherwise not.
73	n/a	assert imp.lock_held()
74	n/a	with self.lock:
75	n/a	self.numcalls += 1
76	n/a	x = self.x
77	n/a	time.sleep(0.01)
78	n/a	self.x = x + 1
79	n/a
80	n/a	class FlushingFinder:
81	n/a	"""A dummy finder which flushes sys.path_importer_cache when it gets
82	n/a	called."""
83	n/a
84	n/a	def find_spec(self, name, path=None, target=None):
85	n/a	sys.path_importer_cache.clear()
86	n/a
87	n/a
88	n/a	class ThreadedImportTests(unittest.TestCase):
89	n/a
90	n/a	def setUp(self):
91	n/a	self.old_random = sys.modules.pop('random', None)
92	n/a
93	n/a	def tearDown(self):
94	n/a	# If the `random` module was already initialized, we restore the
95	n/a	# old module at the end so that pickling tests don't fail.
96	n/a	# See http://bugs.python.org/issue3657#msg110461
97	n/a	if self.old_random is not None:
98	n/a	sys.modules['random'] = self.old_random
99	n/a
100	n/a	def check_parallel_module_init(self):
101	n/a	if imp.lock_held():
102	n/a	# This triggers on, e.g., from test import autotest.
103	n/a	raise unittest.SkipTest("can't run when import lock is held")
104	n/a
105	n/a	done = threading.Event()
106	n/a	for N in (20, 50) * 3:
107	n/a	if verbose:
108	n/a	print("Trying", N, "threads ...", end=' ')
109	n/a	# Make sure that random and modulefinder get reimported freshly
110	n/a	for modname in ['random', 'modulefinder']:
111	n/a	try:
112	n/a	del sys.modules[modname]
113	n/a	except KeyError:
114	n/a	pass
115	n/a	errors = []
116	n/a	done_tasks = []
117	n/a	done.clear()
118	n/a	t0 = time.monotonic()
119	n/a	with start_threads(threading.Thread(target=task,
120	n/a	args=(N, done, done_tasks, errors,))
121	n/a	for i in range(N)):
122	n/a	pass
123	n/a	completed = done.wait(10 * 60)
124	n/a	dt = time.monotonic() - t0
125	n/a	if verbose:
126	n/a	print("%.1f ms" % (dt*1e3), flush=True, end=" ")
127	n/a	dbg_info = 'done: %s/%s' % (len(done_tasks), N)
128	n/a	self.assertFalse(errors, dbg_info)
129	n/a	self.assertTrue(completed, dbg_info)
130	n/a	if verbose:
131	n/a	print("OK.")
132	n/a
133	n/a	def test_parallel_module_init(self):
134	n/a	self.check_parallel_module_init()
135	n/a
136	n/a	def test_parallel_meta_path(self):
137	n/a	finder = Finder()
138	n/a	sys.meta_path.insert(0, finder)
139	n/a	try:
140	n/a	self.check_parallel_module_init()
141	n/a	self.assertGreater(finder.numcalls, 0)
142	n/a	self.assertEqual(finder.x, finder.numcalls)
143	n/a	finally:
144	n/a	sys.meta_path.remove(finder)
145	n/a
146	n/a	def test_parallel_path_hooks(self):
147	n/a	# Here the Finder instance is only used to check concurrent calls
148	n/a	# to path_hook().
149	n/a	finder = Finder()
150	n/a	# In order for our path hook to be called at each import, we need
151	n/a	# to flush the path_importer_cache, which we do by registering a
152	n/a	# dedicated meta_path entry.
153	n/a	flushing_finder = FlushingFinder()
154	n/a	def path_hook(path):
155	n/a	finder.find_spec('')
156	n/a	raise ImportError
157	n/a	sys.path_hooks.insert(0, path_hook)
158	n/a	sys.meta_path.append(flushing_finder)
159	n/a	try:
160	n/a	# Flush the cache a first time
161	n/a	flushing_finder.find_spec('')
162	n/a	numtests = self.check_parallel_module_init()
163	n/a	self.assertGreater(finder.numcalls, 0)
164	n/a	self.assertEqual(finder.x, finder.numcalls)
165	n/a	finally:
166	n/a	sys.meta_path.remove(flushing_finder)
167	n/a	sys.path_hooks.remove(path_hook)
168	n/a
169	n/a	def test_import_hangers(self):
170	n/a	# In case this test is run again, make sure the helper module
171	n/a	# gets loaded from scratch again.
172	n/a	try:
173	n/a	del sys.modules['test.threaded_import_hangers']
174	n/a	except KeyError:
175	n/a	pass
176	n/a	import test.threaded_import_hangers
177	n/a	self.assertFalse(test.threaded_import_hangers.errors)
178	n/a
179	n/a	def test_circular_imports(self):
180	n/a	# The goal of this test is to exercise implementations of the import
181	n/a	# lock which use a per-module lock, rather than a global lock.
182	n/a	# In these implementations, there is a possible deadlock with
183	n/a	# circular imports, for example:
184	n/a	# - thread 1 imports A (grabbing the lock for A) which imports B
185	n/a	# - thread 2 imports B (grabbing the lock for B) which imports A
186	n/a	# Such implementations should be able to detect such situations and
187	n/a	# resolve them one way or the other, without freezing.
188	n/a	# NOTE: our test constructs a slightly less trivial import cycle,
189	n/a	# in order to better stress the deadlock avoidance mechanism.
190	n/a	delay = 0.5
191	n/a	os.mkdir(TESTFN)
192	n/a	self.addCleanup(shutil.rmtree, TESTFN)
193	n/a	sys.path.insert(0, TESTFN)
194	n/a	self.addCleanup(sys.path.remove, TESTFN)
195	n/a	for name, contents in circular_imports_modules.items():
196	n/a	contents = contents % {'delay': delay}
197	n/a	with open(os.path.join(TESTFN, name + ".py"), "wb") as f:
198	n/a	f.write(contents.encode('utf-8'))
199	n/a	self.addCleanup(forget, name)
200	n/a
201	n/a	importlib.invalidate_caches()
202	n/a	results = []
203	n/a	def import_ab():
204	n/a	import A
205	n/a	results.append(getattr(A, 'x', None))
206	n/a	def import_ba():
207	n/a	import B
208	n/a	results.append(getattr(B, 'x', None))
209	n/a	t1 = threading.Thread(target=import_ab)
210	n/a	t2 = threading.Thread(target=import_ba)
211	n/a	t1.start()
212	n/a	t2.start()
213	n/a	t1.join()
214	n/a	t2.join()
215	n/a	self.assertEqual(set(results), {'a', 'b'})
216	n/a
217	n/a	def test_side_effect_import(self):
218	n/a	code = """if 1:
219	n/a	import threading
220	n/a	def target():
221	n/a	import random
222	n/a	t = threading.Thread(target=target)
223	n/a	t.start()
224	n/a	t.join()"""
225	n/a	sys.path.insert(0, os.curdir)
226	n/a	self.addCleanup(sys.path.remove, os.curdir)
227	n/a	filename = TESTFN + ".py"
228	n/a	with open(filename, "wb") as f:
229	n/a	f.write(code.encode('utf-8'))
230	n/a	self.addCleanup(unlink, filename)
231	n/a	self.addCleanup(forget, TESTFN)
232	n/a	self.addCleanup(rmtree, '__pycache__')
233	n/a	importlib.invalidate_caches()
234	n/a	__import__(TESTFN)
235	n/a
236	n/a
237	n/a	@reap_threads
238	n/a	def test_main():
239	n/a	old_switchinterval = None
240	n/a	try:
241	n/a	old_switchinterval = sys.getswitchinterval()
242	n/a	sys.setswitchinterval(1e-5)
243	n/a	except AttributeError:
244	n/a	pass
245	n/a	try:
246	n/a	run_unittest(ThreadedImportTests)
247	n/a	finally:
248	n/a	if old_switchinterval is not None:
249	n/a	sys.setswitchinterval(old_switchinterval)
250	n/a
251	n/a	if __name__ == "__main__":
252	n/a	test_main()