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//usr/lib/python2.4/test/test_threaded_import.py
# 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 from test.test_support import verbose, TestSkipped 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() # 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 TestSkipped("can't run when import lock is held") done.acquire() for N in (20, 50) * 3: if verbose: print "Trying", N, "threads ...", for i in range(N): thread.start_new_thread(task, ()) done.acquire() if verbose: print "OK." done.release() if __name__ == "__main__": test_main()