Lib/test/test_threaded_import.py

   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_support import verbose
  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     if N == 0:
  21         done.release()
  22     critical_section.release()
  23
  24 # Tricky:  When regrtest imports this module, the thread running regrtest
  25 # grabs the import lock and won't let go of it until this module returns.
  26 # All other threads attempting an import hang for the duration.  Since
  27 # this test spawns threads that do little *but* import, we can't do that
  28 # successfully until after this module finishes importing and regrtest
  29 # regains control.  To make this work, a special case was added to
  30 # regrtest to invoke a module's "test_main" function (if any) after
  31 # importing it.
  32
  33 def test_main():        # magic name!  see above
  34     global N, done
  35     done.acquire()
  36     for N in (20, 50) * 3:
  37         if verbose:
  38             print "Trying", N, "threads ...",
  39         for i in range(N):
  40             thread.start_new_thread(task, ())
  41         done.acquire()
  42         if verbose:
  43             print "OK."
  44
  45 if __name__ == "__main__":
  46     test_main()