From ff6d5c044a017364f291dc792b500dba8f7e55f0 Mon Sep 17 00:00:00 2001 From: Antoine Pitrou Date: Sun, 22 Aug 2010 20:46:30 +0000 Subject: [PATCH] Merged revisions 84258,84268 via svnmerge from svn+ssh://pythondev@svn.python.org/python/branches/py3k MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit ........ r84258 | antoine.pitrou | 2010-08-22 12:18:36 +0200 (dim., 22 août 2010) | 4 lines Test that calls to path hooks and meta_path entries are serialized by the import lock. (part of issue #9251) ........ r84268 | antoine.pitrou | 2010-08-22 22:43:26 +0200 (dim., 22 août 2010) | 4 lines Add an import lock test for multithreaded circular imports. (part of #9657) ........ --- Lib/test/test_threaded_import.py | 148 +++++++++++++++++++++++++++++-- 1 file changed, 139 insertions(+), 9 deletions(-) diff --git a/Lib/test/test_threaded_import.py b/Lib/test/test_threaded_import.py index 6cedb9615b..8884fa8182 100644 --- a/Lib/test/test_threaded_import.py +++ b/Lib/test/test_threaded_import.py @@ -5,15 +5,26 @@ # complains several times about module random having no attribute # randrange, and then Python hangs. +import os import imp import sys +import time +import shutil import unittest -from test.support import verbose, TestFailed, import_module, run_unittest +from test.support import verbose, import_module, run_unittest, TESTFN thread = import_module('_thread') +threading = import_module('threading') def task(N, done, done_tasks, errors): try: - import random + # 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: @@ -24,6 +35,52 @@ def task(N, done, done_tasks, errors): if finished: done.release() +# 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_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): @@ -37,7 +94,7 @@ class ThreadedImportTests(unittest.TestCase): if self.old_random is not None: sys.modules['random'] = self.old_random - def test_parallel_module_init(self): + 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") @@ -47,11 +104,12 @@ class ThreadedImportTests(unittest.TestCase): for N in (20, 50) * 3: if verbose: print("Trying", N, "threads ...", end=' ') - # Make sure that random gets reimported freshly - try: - del sys.modules['random'] - except KeyError: - pass + # 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): @@ -62,6 +120,42 @@ class ThreadedImportTests(unittest.TestCase): 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. @@ -72,10 +166,46 @@ class ThreadedImportTests(unittest.TestCase): 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(sys.modules.pop, name, None) + + 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'}) + def test_main(): run_unittest(ThreadedImportTests) - if __name__ == "__main__": test_main() -- 2.40.0