New test adapted from the ancient Demo/threads/bug.py.

ICK ALERT:  read the long comment block before run_the_test().  It was
almost impossible to get this to run without instant deadlock, and the
solution here sucks on several counts.  If you can dream up a better way,
let me know!

Lib/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
+
+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
+    if N == 0:
+        done.release()
+    critical_section.release()
+
+# Tricky, tricky, 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.  So we have to spawn
+# a thread to run the test and return to regrtest.py right away, else the
+# test can't make progress.
+#
+# One miserable consequence:  This test can't wait to make sure all the
+# threads complete!
+#
+# Another:  If this test fails, the output may show up while running
+# some other test.
+#
+# Another:  If you run this test directly, the OS will probably kill
+# all the threads right away, because the program exits immediately
+# after spawning a thread to run the real test.
+#
+# Another:  If this test ever does fail and you attempt to run it by
+# itself via regrtest, the same applies:  regrtest will get out so fast
+# the OS will kill all the threads here.
+
+def run_the_test():
+    global N, done
+    done.acquire()
+    for N in [1, 2, 3, 4, 20, 4, 3, 2]:
+        for i in range(N):
+            thread.start_new_thread(task, ())
+        done.acquire()
+
+thread.start_new_thread(run_the_test, ())