| # 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 |
| import unittest |
| 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() |