[Python-checkins] r84269 - in python/branches/release31-maint: Lib/test/test_threaded_import.py
antoine.pitrou
python-checkins at python.org
Sun Aug 22 22:46:30 CEST 2010
Author: antoine.pitrou
Date: Sun Aug 22 22:46:30 2010
New Revision: 84269
Log:
Merged revisions 84258,84268 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k
........
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)
........
Modified:
python/branches/release31-maint/ (props changed)
python/branches/release31-maint/Lib/test/test_threaded_import.py
Modified: python/branches/release31-maint/Lib/test/test_threaded_import.py
==============================================================================
--- python/branches/release31-maint/Lib/test/test_threaded_import.py (original)
+++ python/branches/release31-maint/Lib/test/test_threaded_import.py Sun Aug 22 22:46:30 2010
@@ -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 @@
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 @@
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 @@
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 @@
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 @@
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()
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