Lib/test/test_fork1.py

   1 """This test checks for correct fork() behavior.
   2 """
   3
   4 import imp
   5 import os
   6 import signal
   7 import sys
   8 import time
   9
  10 from test.fork_wait import ForkWait
  11 from test.test_support import run_unittest, reap_children, get_attribute, import_module
  12 threading = import_module('threading')
  13
  14 #Skip test if fork does not exist.
  15 get_attribute(os, 'fork')
  16
  17
  18 class ForkTest(ForkWait):
  19     def wait_impl(self, cpid):
  20         for i in range(10):
  21             # waitpid() shouldn't hang, but some of the buildbots seem to hang
  22             # in the forking tests.  This is an attempt to fix the problem.
  23             spid, status = os.waitpid(cpid, os.WNOHANG)
  24             if spid == cpid:
  25                 break
  26             time.sleep(1.0)
  27
  28         self.assertEqual(spid, cpid)
  29         self.assertEqual(status, 0, "cause = %d, exit = %d" % (status&0xff, status>>8))
  30
  31     def test_import_lock_fork(self):
  32         import_started = threading.Event()
  33         fake_module_name = "fake test module"
  34         partial_module = "partial"
  35         complete_module = "complete"
  36         def importer():
  37             imp.acquire_lock()
  38             sys.modules[fake_module_name] = partial_module
  39             import_started.set()
  40             time.sleep(0.01) # Give the other thread time to try and acquire.
  41             sys.modules[fake_module_name] = complete_module
  42             imp.release_lock()
  43         t = threading.Thread(target=importer)
  44         t.start()
  45         import_started.wait()
  46         pid = os.fork()
  47         try:
  48             if not pid:
  49                 m = __import__(fake_module_name)
  50                 if m == complete_module:
  51                     os._exit(0)
  52                 else:
  53                     os._exit(1)
  54             else:
  55                 t.join()
  56                 # Exitcode 1 means the child got a partial module (bad.) No
  57                 # exitcode (but a hang, which manifests as 'got pid 0')
  58                 # means the child deadlocked (also bad.)
  59                 self.wait_impl(pid)
  60         finally:
  61             try:
  62                 os.kill(pid, signal.SIGKILL)
  63             except OSError:
  64                 pass
  65
  66 def test_main():
  67     run_unittest(ForkTest)
  68     reap_children()
  69
  70 if __name__ == "__main__":
  71     test_main()