1 # This is a variant of the very old (early 90's) file

     2 # Demo/threads/bug.py.  It simply provokes a number of threads into

     3 # trying to import the same module "at the same time".

     4 # There are no pleasant failure modes -- most likely is that Python

     5 # complains several times about module random having no attribute

     6 # randrange, and then Python hangs.

     7 

     8 import thread

     9 from test.test_support import verbose, TestSkipped, TestFailed

    10 

    11 critical_section = thread.allocate_lock()

    12 done = thread.allocate_lock()

    13 

    14 def task():

    15     global N, critical_section, done

    16     import random

    17     x = random.randrange(1, 3)

    18     critical_section.acquire()

    19     N -= 1

    20     # Must release critical_section before releasing done, else the main

    21     # thread can exit and set critical_section to None as part of global

    22     # teardown; then critical_section.release() raises AttributeError.

    23     finished = N == 0

    24     critical_section.release()

    25     if finished:

    26         done.release()

    27 

    28 def test_import_hangers():

    29     import sys

    30     if verbose:

    31         print "testing import hangers ...",

    32 

    33     import test.threaded_import_hangers

    34     try:

    35         if test.threaded_import_hangers.errors:

    36             raise TestFailed(test.threaded_import_hangers.errors)

    37         elif verbose:

    38             print "OK."

    39     finally:

    40         # In case this test is run again, make sure the helper module

    41         # gets loaded from scratch again.

    42         del sys.modules['test.threaded_import_hangers']

    43 

    44 # Tricky:  When regrtest imports this module, the thread running regrtest

    45 # grabs the import lock and won't let go of it until this module returns.

    46 # All other threads attempting an import hang for the duration.  Since

    47 # this test spawns threads that do little *but* import, we can't do that

    48 # successfully until after this module finishes importing and regrtest

    49 # regains control.  To make this work, a special case was added to

    50 # regrtest to invoke a module's "test_main" function (if any) after

    51 # importing it.

    52 

    53 def test_main():        # magic name!  see above

    54     global N, done

    55 

    56     import imp

    57     if imp.lock_held():

    58         # This triggers on, e.g., from test import autotest.

    59         raise TestSkipped("can't run when import lock is held")

    60 

    61     done.acquire()

    62     for N in (20, 50) * 3:

    63         if verbose:

    64             print "Trying", N, "threads ...",

    65         for i in range(N):

    66             thread.start_new_thread(task, ())

    67         done.acquire()

    68         if verbose:

    69             print "OK."

    70     done.release()

    71 

    72     test_import_hangers()

    73 

    74 if __name__ == "__main__":

    75     test_main()