| # 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 |
| import sys |
| import time |
| import unittest |
| from test.support import verbose, TestFailed, import_module, run_unittest |
| thread = import_module('_thread') |
| |
| 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(thread.get_ident()) |
| finished = len(done_tasks) == N |
| if finished: |
| done.release() |
| |
| |
| class Finder: |
| """A dummy finder to detect concurrent access to its find_module() |
| method.""" |
| |
| def __init__(self): |
| self.numcalls = 0 |
| self.x = 0 |
| self.lock = thread.allocate_lock() |
| |
| def find_module(self, name, path=None): |
| # Simulate some thread-unsafe behaviour. If calls to find_module() |
| # are properly serialized, `x` will end up the same as `numcalls`. |
| # Otherwise not. |
| with self.lock: |
| self.numcalls += 1 |
| x = self.x |
| time.sleep(0.1) |
| self.x = x + 1 |
| |
| class FlushingFinder: |
| """A dummy finder which flushes sys.path_importer_cache when it gets |
| called.""" |
| |
| def find_module(self, name, path=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 |
| |
| def check_parallel_module_init(self): |
| 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 = thread.allocate_lock() |
| done.acquire() |
| 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 = [] |
| for i in range(N): |
| thread.start_new_thread(task, (N, done, done_tasks, errors,)) |
| done.acquire() |
| self.assertFalse(errors) |
| if verbose: |
| print("OK.") |
| done.release() |
| |
| def test_parallel_module_init(self): |
| self.check_parallel_module_init() |
| |
| def test_parallel_meta_path(self): |
| finder = Finder() |
| sys.meta_path.append(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_module('') |
| raise ImportError |
| sys.path_hooks.append(path_hook) |
| sys.meta_path.append(flushing_finder) |
| try: |
| # Flush the cache a first time |
| flushing_finder.find_module('') |
| 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_main(): |
| run_unittest(ThreadedImportTests) |
| |
| |
| if __name__ == "__main__": |
| test_main() |