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author | Kyle Stanley <aeros167@gmail.com> | 2019-07-05 21:22:42 (GMT) |
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committer | Brett Cannon <54418+brettcannon@users.noreply.github.com> | 2019-07-05 21:22:42 (GMT) |
commit | bad02cc3c881e5b55e1d3db5a3ce3aaf02ce8536 (patch) | |
tree | e55c9569609142c913119b1e7c8e8972df9c1880 /Lib/test/test_importlib | |
parent | 7b57c03a7cb63ccfb2b8dfa82a1bf169268d80ba (diff) | |
download | cpython-bad02cc3c881e5b55e1d3db5a3ce3aaf02ce8536.zip cpython-bad02cc3c881e5b55e1d3db5a3ce3aaf02ce8536.tar.gz cpython-bad02cc3c881e5b55e1d3db5a3ce3aaf02ce8536.tar.bz2 |
Move test_threaded_import.py to test_importlib/ (GH-14582)
Diffstat (limited to 'Lib/test/test_importlib')
-rw-r--r-- | Lib/test/test_importlib/test_threaded_import.py | 263 |
1 files changed, 263 insertions, 0 deletions
diff --git a/Lib/test/test_importlib/test_threaded_import.py b/Lib/test/test_importlib/test_threaded_import.py new file mode 100644 index 0000000..8607f36 --- /dev/null +++ b/Lib/test/test_importlib/test_threaded_import.py @@ -0,0 +1,263 @@ +# This is a variant of the very old (early 90's) file +# Demo/threads/bug.py. It simply provokes a number of threads into +# trying to import the same module "at the same time". +# There are no pleasant failure modes -- most likely is that Python +# complains several times about module random having no attribute +# randrange, and then Python hangs. + +import _imp as imp +import os +import importlib +import sys +import time +import shutil +import threading +import unittest +from unittest import mock +from test.support import ( + verbose, run_unittest, TESTFN, reap_threads, + forget, unlink, rmtree, start_threads) + +def task(N, done, done_tasks, errors): + try: + # We don't use modulefinder but still import it in order to stress + # importing of different modules from several threads. + if len(done_tasks) % 2: + import modulefinder + import random + else: + import random + import modulefinder + # This will fail if random is not completely initialized + x = random.randrange(1, 3) + except Exception as e: + errors.append(e.with_traceback(None)) + finally: + done_tasks.append(threading.get_ident()) + finished = len(done_tasks) == N + if finished: + done.set() + +def mock_register_at_fork(func): + # bpo-30599: Mock os.register_at_fork() when importing the random module, + # since this function doesn't allow to unregister callbacks and would leak + # memory. + return mock.patch('os.register_at_fork', create=True)(func) + +# Create a circular import structure: A -> C -> B -> D -> A +# NOTE: `time` is already loaded and therefore doesn't threaten to deadlock. + +circular_imports_modules = { + 'A': """if 1: + import time + time.sleep(%(delay)s) + x = 'a' + import C + """, + 'B': """if 1: + import time + time.sleep(%(delay)s) + x = 'b' + import D + """, + 'C': """import B""", + 'D': """import A""", +} + +class Finder: + """A dummy finder to detect concurrent access to its find_spec() + method.""" + + def __init__(self): + self.numcalls = 0 + self.x = 0 + self.lock = threading.Lock() + + def find_spec(self, name, path=None, target=None): + # Simulate some thread-unsafe behaviour. If calls to find_spec() + # are properly serialized, `x` will end up the same as `numcalls`. + # Otherwise not. + assert imp.lock_held() + with self.lock: + self.numcalls += 1 + x = self.x + time.sleep(0.01) + self.x = x + 1 + +class FlushingFinder: + """A dummy finder which flushes sys.path_importer_cache when it gets + called.""" + + def find_spec(self, name, path=None, target=None): + sys.path_importer_cache.clear() + + +class ThreadedImportTests(unittest.TestCase): + + def setUp(self): + self.old_random = sys.modules.pop('random', None) + + def tearDown(self): + # If the `random` module was already initialized, we restore the + # old module at the end so that pickling tests don't fail. + # See http://bugs.python.org/issue3657#msg110461 + if self.old_random is not None: + sys.modules['random'] = self.old_random + + @mock_register_at_fork + def check_parallel_module_init(self, mock_os): + if imp.lock_held(): + # This triggers on, e.g., from test import autotest. + raise unittest.SkipTest("can't run when import lock is held") + + done = threading.Event() + for N in (20, 50) * 3: + if verbose: + print("Trying", N, "threads ...", end=' ') + # Make sure that random and modulefinder get reimported freshly + for modname in ['random', 'modulefinder']: + try: + del sys.modules[modname] + except KeyError: + pass + errors = [] + done_tasks = [] + done.clear() + t0 = time.monotonic() + with start_threads(threading.Thread(target=task, + args=(N, done, done_tasks, errors,)) + for i in range(N)): + pass + completed = done.wait(10 * 60) + dt = time.monotonic() - t0 + if verbose: + print("%.1f ms" % (dt*1e3), flush=True, end=" ") + dbg_info = 'done: %s/%s' % (len(done_tasks), N) + self.assertFalse(errors, dbg_info) + self.assertTrue(completed, dbg_info) + if verbose: + print("OK.") + + def test_parallel_module_init(self): + self.check_parallel_module_init() + + def test_parallel_meta_path(self): + finder = Finder() + sys.meta_path.insert(0, finder) + try: + self.check_parallel_module_init() + self.assertGreater(finder.numcalls, 0) + self.assertEqual(finder.x, finder.numcalls) + finally: + sys.meta_path.remove(finder) + + def test_parallel_path_hooks(self): + # Here the Finder instance is only used to check concurrent calls + # to path_hook(). + finder = Finder() + # In order for our path hook to be called at each import, we need + # to flush the path_importer_cache, which we do by registering a + # dedicated meta_path entry. + flushing_finder = FlushingFinder() + def path_hook(path): + finder.find_spec('') + raise ImportError + sys.path_hooks.insert(0, path_hook) + sys.meta_path.append(flushing_finder) + try: + # Flush the cache a first time + flushing_finder.find_spec('') + numtests = self.check_parallel_module_init() + self.assertGreater(finder.numcalls, 0) + self.assertEqual(finder.x, finder.numcalls) + finally: + sys.meta_path.remove(flushing_finder) + sys.path_hooks.remove(path_hook) + + def test_import_hangers(self): + # In case this test is run again, make sure the helper module + # gets loaded from scratch again. + try: + del sys.modules['test.threaded_import_hangers'] + except KeyError: + pass + import test.threaded_import_hangers + self.assertFalse(test.threaded_import_hangers.errors) + + def test_circular_imports(self): + # The goal of this test is to exercise implementations of the import + # lock which use a per-module lock, rather than a global lock. + # In these implementations, there is a possible deadlock with + # circular imports, for example: + # - thread 1 imports A (grabbing the lock for A) which imports B + # - thread 2 imports B (grabbing the lock for B) which imports A + # Such implementations should be able to detect such situations and + # resolve them one way or the other, without freezing. + # NOTE: our test constructs a slightly less trivial import cycle, + # in order to better stress the deadlock avoidance mechanism. + delay = 0.5 + os.mkdir(TESTFN) + self.addCleanup(shutil.rmtree, TESTFN) + sys.path.insert(0, TESTFN) + self.addCleanup(sys.path.remove, TESTFN) + for name, contents in circular_imports_modules.items(): + contents = contents % {'delay': delay} + with open(os.path.join(TESTFN, name + ".py"), "wb") as f: + f.write(contents.encode('utf-8')) + self.addCleanup(forget, name) + + importlib.invalidate_caches() + results = [] + def import_ab(): + import A + results.append(getattr(A, 'x', None)) + def import_ba(): + import B + results.append(getattr(B, 'x', None)) + t1 = threading.Thread(target=import_ab) + t2 = threading.Thread(target=import_ba) + t1.start() + t2.start() + t1.join() + t2.join() + self.assertEqual(set(results), {'a', 'b'}) + + @mock_register_at_fork + def test_side_effect_import(self, mock_os): + code = """if 1: + import threading + def target(): + import random + t = threading.Thread(target=target) + t.start() + t.join() + t = None""" + sys.path.insert(0, os.curdir) + self.addCleanup(sys.path.remove, os.curdir) + filename = TESTFN + ".py" + with open(filename, "wb") as f: + f.write(code.encode('utf-8')) + self.addCleanup(unlink, filename) + self.addCleanup(forget, TESTFN) + self.addCleanup(rmtree, '__pycache__') + importlib.invalidate_caches() + __import__(TESTFN) + del sys.modules[TESTFN] + + +@reap_threads +def test_main(): + old_switchinterval = None + try: + old_switchinterval = sys.getswitchinterval() + sys.setswitchinterval(1e-5) + except AttributeError: + pass + try: + run_unittest(ThreadedImportTests) + finally: + if old_switchinterval is not None: + sys.setswitchinterval(old_switchinterval) + +if __name__ == "__main__": + test_main() |