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# 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 _thread as thread
from test.support import verbose, TestFailed
critical_section = thread.allocate_lock()
done = thread.allocate_lock()
def task():
global N, critical_section, done
import random
x = random.randrange(1, 3)
critical_section.acquire()
N -= 1
# Must release critical_section before releasing done, else the main
# thread can exit and set critical_section to None as part of global
# teardown; then critical_section.release() raises AttributeError.
finished = N == 0
critical_section.release()
if finished:
done.release()
def test_import_hangers():
import sys
if verbose:
print("testing import hangers ...", end=' ')
import test.threaded_import_hangers
try:
if test.threaded_import_hangers.errors:
raise TestFailed(test.threaded_import_hangers.errors)
elif verbose:
print("OK.")
finally:
# In case this test is run again, make sure the helper module
# gets loaded from scratch again.
del sys.modules['test.threaded_import_hangers']
# Tricky: When regrtest imports this module, the thread running regrtest
# grabs the import lock and won't let go of it until this module returns.
# All other threads attempting an import hang for the duration. Since
# this test spawns threads that do little *but* import, we can't do that
# successfully until after this module finishes importing and regrtest
# regains control. To make this work, a special case was added to
# regrtest to invoke a module's "test_main" function (if any) after
# importing it.
def test_main(): # magic name! see above
global N, done
import imp
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.acquire()
for N in (20, 50) * 3:
if verbose:
print("Trying", N, "threads ...", end=' ')
for i in range(N):
thread.start_new_thread(task, ())
done.acquire()
if verbose:
print("OK.")
done.release()
test_import_hangers()
if __name__ == "__main__":
test_main()
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