Merge.

14 files changed, 294 insertions, 208 deletions

diff --git a/Lib/_dummy_thread.py b/Lib/_dummy_thread.py
index 13b1f26..b67cfb9 100644
--- a/Lib/_dummy_thread.py
+++ b/Lib/_dummy_thread.py
@@ -81,6 +81,10 @@ def stack_size(size=None):
         raise error("setting thread stack size not supported")
     return 0
 
+def _set_sentinel():
+    """Dummy implementation of _thread._set_sentinel()."""
+    return LockType()
+
 class LockType(object):
     """Class implementing dummy implementation of _thread.LockType.
 
diff --git a/Lib/decimal.py b/Lib/decimal.py
index d39ac1d..fc95ae9 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -21,7 +21,7 @@ the General Decimal Arithmetic Specification:
 
 and IEEE standard 854-1987:
 
-    www.cs.berkeley.edu/~ejr/projects/754/private/drafts/854-1987/dir.html
+    http://en.wikipedia.org/wiki/IEEE_854-1987
 
 Decimal floating point has finite precision with arbitrarily large bounds.
 
diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py
index 59fb664..27fda9f 100644
--- a/Lib/multiprocessing/connection.py
+++ b/Lib/multiprocessing/connection.py
@@ -878,13 +878,21 @@ else:
 
     import selectors
 
+    # poll/select have the advantage of not requiring any extra file
+    # descriptor, contrarily to epoll/kqueue (also, they require a single
+    # syscall).
+    if hasattr(selectors, 'PollSelector'):
+        _WaitSelector = selectors.PollSelector
+    else:
+        _WaitSelector = selectors.SelectSelector
+
     def wait(object_list, timeout=None):
         '''
         Wait till an object in object_list is ready/readable.
 
         Returns list of those objects in object_list which are ready/readable.
         '''
-        with selectors.DefaultSelector() as selector:
+        with _WaitSelector() as selector:
             for obj in object_list:
                 selector.register(obj, selectors.EVENT_READ)
 
diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index 5832ef6..5687ef9 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -860,24 +860,31 @@ if hasattr(os, "umask"):
         finally:
             os.umask(oldmask)
 
-# TEST_HOME refers to the top level directory of the "test" package
+# TEST_HOME_DIR refers to the top level directory of the "test" package
 # that contains Python's regression test suite
-TEST_HOME = os.path.dirname(os.path.abspath(__file__))
+TEST_SUPPORT_DIR = os.path.dirname(os.path.abspath(__file__))
+TEST_HOME_DIR = os.path.dirname(TEST_SUPPORT_DIR)
 
-def findfile(file, here=TEST_HOME, subdir=None):
+# TEST_DATA_DIR is used as a target download location for remote resources
+TEST_DATA_DIR = os.path.join(TEST_HOME_DIR, "data")
+
+def findfile(filename, subdir=None):
     """Try to find a file on sys.path or in the test directory.  If it is not
     found the argument passed to the function is returned (this does not
-    necessarily signal failure; could still be the legitimate path)."""
-    if os.path.isabs(file):
-        return file
+    necessarily signal failure; could still be the legitimate path).
+
+    Setting *subdir* indicates a relative path to use to find the file
+    rather than looking directly in the path directories.
+    """
+    if os.path.isabs(filename):
+        return filename
     if subdir is not None:
-        file = os.path.join(subdir, file)
-    path = sys.path
-    path = [os.path.dirname(here)] + path
+        filename = os.path.join(subdir, filename)
+    path = [TEST_HOME_DIR] + sys.path
     for dn in path:
-        fn = os.path.join(dn, file)
+        fn = os.path.join(dn, filename)
         if os.path.exists(fn): return fn
-    return file
+    return filename
 
 def create_empty_file(filename):
     """Create an empty file. If the file already exists, truncate it."""
@@ -914,7 +921,7 @@ def open_urlresource(url, *args, **kw):
 
     filename = urllib.parse.urlparse(url)[2].split('/')[-1] # '/': it's URL!
 
-    fn = os.path.join(os.path.dirname(__file__), "data", filename)
+    fn = os.path.join(TEST_DATA_DIR, filename)
 
     def check_valid_file(fn):
         f = open(fn, *args, **kw)
diff --git a/Lib/test/test_faulthandler.py b/Lib/test/test_faulthandler.py
index 4a8becf..d78bcb0 100644
--- a/Lib/test/test_faulthandler.py
+++ b/Lib/test/test_faulthandler.py
@@ -265,17 +265,33 @@ faulthandler._sigsegv()
         # By default, the module should be disabled
         code = "import faulthandler; print(faulthandler.is_enabled())"
         args = (sys.executable, '-E', '-c', code)
-        # use subprocess module directly because test.script_helper adds
-        # "-X faulthandler" to the command line
-        stdout = subprocess.check_output(args)
-        self.assertEqual(stdout.rstrip(), b"False")
+        # don't use assert_python_ok() because it always enable faulthandler
+        output = subprocess.check_output(args)
+        self.assertEqual(output.rstrip(), b"False")
 
     def test_sys_xoptions(self):
         # Test python -X faulthandler
         code = "import faulthandler; print(faulthandler.is_enabled())"
-        rc, stdout, stderr = assert_python_ok("-X", "faulthandler", "-c", code)
-        stdout = (stdout + stderr).strip()
-        self.assertEqual(stdout, b"True")
+        args = (sys.executable, "-E", "-X", "faulthandler", "-c", code)
+        # don't use assert_python_ok() because it always enable faulthandler
+        output = subprocess.check_output(args)
+        self.assertEqual(output.rstrip(), b"True")
+
+    def test_env_var(self):
+        # empty env var
+        code = "import faulthandler; print(faulthandler.is_enabled())"
+        args = (sys.executable, "-c", code)
+        env = os.environ.copy()
+        env['PYTHONFAULTHANDLER'] = ''
+        # don't use assert_python_ok() because it always enable faulthandler
+        output = subprocess.check_output(args, env=env)
+        self.assertEqual(output.rstrip(), b"False")
+
+        # non-empty env var
+        env = os.environ.copy()
+        env['PYTHONFAULTHANDLER'] = '1'
+        output = subprocess.check_output(args, env=env)
+        self.assertEqual(output.rstrip(), b"True")
 
     def check_dump_traceback(self, filename):
         """
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index d0dd364..39b0e80 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -34,6 +34,10 @@ try:
     import resource
 except ImportError:
     resource = None
+try:
+    import fcntl
+except ImportError:
+    fcntl = None
 
 from test.script_helper import assert_python_ok
 
@@ -2300,19 +2304,38 @@ class CPUCountTests(unittest.TestCase):
 
 
 class FDInheritanceTests(unittest.TestCase):
-    def test_get_inheritable(self):
+    def test_get_set_inheritable(self):
         fd = os.open(__file__, os.O_RDONLY)
         self.addCleanup(os.close, fd)
-        for inheritable in (False, True):
-            os.set_inheritable(fd, inheritable)
-            self.assertEqual(os.get_inheritable(fd), inheritable)
+        self.assertEqual(os.get_inheritable(fd), False)
+
+        os.set_inheritable(fd, True)
+        self.assertEqual(os.get_inheritable(fd), True)
 
-    def test_set_inheritable(self):
+    @unittest.skipIf(fcntl is None, "need fcntl")
+    def test_get_inheritable_cloexec(self):
         fd = os.open(__file__, os.O_RDONLY)
         self.addCleanup(os.close, fd)
-        os.set_inheritable(fd, True)
+        self.assertEqual(os.get_inheritable(fd), False)
+
+        # clear FD_CLOEXEC flag
+        flags = fcntl.fcntl(fd, fcntl.F_GETFD)
+        flags &= ~fcntl.FD_CLOEXEC
+        fcntl.fcntl(fd, fcntl.F_SETFD, flags)
+
         self.assertEqual(os.get_inheritable(fd), True)
 
+    @unittest.skipIf(fcntl is None, "need fcntl")
+    def test_set_inheritable_cloexec(self):
+        fd = os.open(__file__, os.O_RDONLY)
+        self.addCleanup(os.close, fd)
+        self.assertEqual(fcntl.fcntl(fd, fcntl.F_GETFD) & fcntl.FD_CLOEXEC,
+                         fcntl.FD_CLOEXEC)
+
+        os.set_inheritable(fd, True)
+        self.assertEqual(fcntl.fcntl(fd, fcntl.F_GETFD) & fcntl.FD_CLOEXEC,
+                         0)
+
     def test_open(self):
         fd = os.open(__file__, os.O_RDONLY)
         self.addCleanup(os.close, fd)
diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py
index 289fb22..353874b 100644
--- a/Lib/test/test_regrtest.py
+++ b/Lib/test/test_regrtest.py
@@ -3,6 +3,7 @@ Tests of regrtest.py.
 """
 
 import argparse
+import faulthandler
 import getopt
 import os.path
 import unittest
@@ -25,6 +26,8 @@ class ParseArgsTestCase(unittest.TestCase):
                     regrtest._parse_args([opt])
                 self.assertIn('Run Python regression tests.', out.getvalue())
 
+    @unittest.skipUnless(hasattr(faulthandler, 'dump_traceback_later'),
+                         "faulthandler.dump_traceback_later() required")
     def test_timeout(self):
         ns = regrtest._parse_args(['--timeout', '4.2'])
         self.assertEqual(ns.timeout, 4.2)
diff --git a/Lib/test/test_selectors.py b/Lib/test/test_selectors.py
index 2657a50..6ce4d8a 100644
--- a/Lib/test/test_selectors.py
+++ b/Lib/test/test_selectors.py
@@ -301,6 +301,7 @@ class BaseSelectorTestCase(unittest.TestCase):
 
 class ScalableSelectorMixIn:
 
+    # see issue #18963 for why it's skipped on older OS X versions
     @support.requires_mac_ver(10, 5)
     @unittest.skipUnless(resource, "Test needs resource module")
     def test_above_fd_setsize(self):
@@ -313,7 +314,7 @@ class ScalableSelectorMixIn:
             self.addCleanup(resource.setrlimit, resource.RLIMIT_NOFILE,
                             (soft, hard))
             NUM_FDS = hard
-        except OSError:
+        except (OSError, ValueError):
             NUM_FDS = soft
 
         # guard for already allocated FDs (stdin, stdout...)
diff --git a/Lib/test/test_site.py b/Lib/test/test_site.py
index 4aff932..34d83f2 100644
--- a/Lib/test/test_site.py
+++ b/Lib/test/test_site.py
@@ -5,6 +5,7 @@ executing have not been removed.
 
 """
 import unittest
+import test.support
 from test.support import run_unittest, TESTFN, EnvironmentVarGuard
 from test.support import captured_stderr
 import builtins
@@ -373,9 +374,10 @@ class ImportSideEffectTests(unittest.TestCase):
         self.assertTrue(hasattr(builtins, "exit"))
 
     def test_setting_copyright(self):
-        # 'copyright' and 'credits' should be in builtins
+        # 'copyright', 'credits', and 'license' should be in builtins
         self.assertTrue(hasattr(builtins, "copyright"))
         self.assertTrue(hasattr(builtins, "credits"))
+        self.assertTrue(hasattr(builtins, "license"))
 
     def test_setting_help(self):
         # 'help' should be set in builtins
@@ -402,5 +404,27 @@ class ImportSideEffectTests(unittest.TestCase):
                 self.fail("sitecustomize not imported automatically")
 
 
+class LicenseURL(unittest.TestCase):
+    """Test accessibility of the license."""
+
+    @unittest.skipUnless(str(license).startswith('See http://'),
+                         'license is available as a file')
+    def test_license_page(self):
+        """urlopen should return the license page"""
+        pat = r'^See (http://www\.python\.org/download/releases/[^/]+/license/)$'
+        mo = re.search(pat, str(license))
+        self.assertIsNotNone(mo, msg='can\'t find appropriate url in license')
+        if mo is not None:
+            url = mo.group(1)
+            with test.support.transient_internet(url):
+                import urllib.request, urllib.error
+                try:
+                    with urllib.request.urlopen(url) as data:
+                        code = data.getcode()
+                except urllib.error.HTTPError as e:
+                    code = e.code
+                self.assertEqual(code, 200, msg=url)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 6205768..490f776 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -26,6 +26,10 @@ try:
     import multiprocessing
 except ImportError:
     multiprocessing = False
+try:
+    import fcntl
+except ImportError:
+    fcntl = None
 
 HOST = support.HOST
 MSG = 'Michael Gilfix was here\u1234\r\n'.encode('utf-8') ## test unicode string and carriage return
@@ -4804,6 +4808,33 @@ class InheritanceTest(unittest.TestCase):
             sock.set_inheritable(False)
             self.assertEqual(sock.get_inheritable(), False)
 
+    @unittest.skipIf(fcntl is None, "need fcntl")
+    def test_get_inheritable_cloexec(self):
+        sock = socket.socket()
+        with sock:
+            fd = sock.fileno()
+            self.assertEqual(sock.get_inheritable(), False)
+
+            # clear FD_CLOEXEC flag
+            flags = fcntl.fcntl(fd, fcntl.F_GETFD)
+            flags &= ~fcntl.FD_CLOEXEC
+            fcntl.fcntl(fd, fcntl.F_SETFD, flags)
+
+            self.assertEqual(sock.get_inheritable(), True)
+
+    @unittest.skipIf(fcntl is None, "need fcntl")
+    def test_set_inheritable_cloexec(self):
+        sock = socket.socket()
+        with sock:
+            fd = sock.fileno()
+            self.assertEqual(fcntl.fcntl(fd, fcntl.F_GETFD) & fcntl.FD_CLOEXEC,
+                             fcntl.FD_CLOEXEC)
+
+            sock.set_inheritable(True)
+            self.assertEqual(fcntl.fcntl(fd, fcntl.F_GETFD) & fcntl.FD_CLOEXEC,
+                             0)
+
+
     @unittest.skipUnless(hasattr(socket, "socketpair"),
                          "need socket.socketpair()")
     def test_socketpair(self):
diff --git a/Lib/test/test_tcl.py b/Lib/test/test_tcl.py
index 4e52fd4..cf717d8 100644
--- a/Lib/test/test_tcl.py
+++ b/Lib/test/test_tcl.py
@@ -15,6 +15,14 @@ support.import_fresh_module('tkinter')
 from tkinter import Tcl
 from _tkinter import TclError
 
+tcl_version = _tkinter.TCL_VERSION.split('.')
+try:
+    for i in range(len(tcl_version)):
+        tcl_version[i] = int(tcl_version[i])
+except ValueError:
+    pass
+tcl_version = tuple(tcl_version)
+
 
 class TkinterTest(unittest.TestCase):
 
@@ -200,9 +208,12 @@ class TclTest(unittest.TestCase):
             (('a', 3.4), ('a', 3.4)),
             ((), ()),
             (call('list', 1, '2', (3.4,)), (1, '2', (3.4,))),
-            (call('dict', 'create', 1, '\u20ac', b'\xe2\x82\xac', (3.4,)),
-                    (1, '\u20ac', '\u20ac', (3.4,))),
         ]
+        if tcl_version >= (8, 5):
+            testcases += [
+                (call('dict', 'create', 1, '\u20ac', b'\xe2\x82\xac', (3.4,)),
+                        (1, '\u20ac', '\u20ac', (3.4,))),
+            ]
         for arg, res in testcases:
             self.assertEqual(splitlist(arg), res, msg=arg)
         self.assertRaises(TclError, splitlist, '{')
@@ -234,9 +245,12 @@ class TclTest(unittest.TestCase):
             (('a', (2, 3.4)), ('a', (2, 3.4))),
             ((), ()),
             (call('list', 1, '2', (3.4,)), (1, '2', (3.4,))),
-            (call('dict', 'create', 12, '\u20ac', b'\xe2\x82\xac', (3.4,)),
-                    (12, '\u20ac', '\u20ac', (3.4,))),
         ]
+        if tcl_version >= (8, 5):
+            testcases += [
+                (call('dict', 'create', 12, '\u20ac', b'\xe2\x82\xac', (3.4,)),
+                        (12, '\u20ac', '\u20ac', (3.4,))),
+            ]
         for arg, res in testcases:
             self.assertEqual(split(arg), res, msg=arg)
 
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index 971a635..75ae247 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -109,7 +109,7 @@ class ThreadTests(BaseTestCase):
         if verbose:
             print('waiting for all tasks to complete')
         for t in threads:
-            t.join(NUMTASKS)
+            t.join()
             self.assertTrue(not t.is_alive())
             self.assertNotEqual(t.ident, 0)
             self.assertFalse(t.ident is None)
@@ -539,6 +539,40 @@ class ThreadTests(BaseTestCase):
         self.assertEqual(err, b"")
         self.assertEqual(data, "Thread-1\nTrue\nTrue\n")
 
+    def test_tstate_lock(self):
+        # Test an implementation detail of Thread objects.
+        started = _thread.allocate_lock()
+        finish = _thread.allocate_lock()
+        started.acquire()
+        finish.acquire()
+        def f():
+            started.release()
+            finish.acquire()
+            time.sleep(0.01)
+        # The tstate lock is None until the thread is started
+        t = threading.Thread(target=f)
+        self.assertIs(t._tstate_lock, None)
+        t.start()
+        started.acquire()
+        self.assertTrue(t.is_alive())
+        # The tstate lock can't be acquired when the thread is running
+        # (or suspended).
+        tstate_lock = t._tstate_lock
+        self.assertFalse(tstate_lock.acquire(timeout=0), False)
+        finish.release()
+        # When the thread ends, the state_lock can be successfully
+        # acquired.
+        self.assertTrue(tstate_lock.acquire(timeout=5), False)
+        # But is_alive() is still True:  we hold _tstate_lock now, which
+        # prevents is_alive() from knowing the thread's end-of-life C code
+        # is done.
+        self.assertTrue(t.is_alive())
+        # Let is_alive() find out the C code is done.
+        tstate_lock.release()
+        self.assertFalse(t.is_alive())
+        # And verify the thread disposed of _tstate_lock.
+        self.assertTrue(t._tstate_lock is None)
+
 
 class ThreadJoinOnShutdown(BaseTestCase):
 
@@ -613,144 +647,8 @@ class ThreadJoinOnShutdown(BaseTestCase):
             """
         self._run_and_join(script)
 
-    def assertScriptHasOutput(self, script, expected_output):
-        rc, out, err = assert_python_ok("-c", script)
-        data = out.decode().replace('\r', '')
-        self.assertEqual(data, expected_output)
-
-    @unittest.skipUnless(hasattr(os, 'fork'), "needs os.fork()")
-    @unittest.skipIf(sys.platform in platforms_to_skip, "due to known OS bug")
-    def test_4_joining_across_fork_in_worker_thread(self):
-        # There used to be a possible deadlock when forking from a child
-        # thread.  See http://bugs.python.org/issue6643.
-
-        # The script takes the following steps:
-        # - The main thread in the parent process starts a new thread and then
-        #   tries to join it.
-        # - The join operation acquires the Lock inside the thread's _block
-        #   Condition.  (See threading.py:Thread.join().)
-        # - We stub out the acquire method on the condition to force it to wait
-        #   until the child thread forks.  (See LOCK ACQUIRED HERE)
-        # - The child thread forks.  (See LOCK HELD and WORKER THREAD FORKS
-        #   HERE)
-        # - The main thread of the parent process enters Condition.wait(),
-        #   which releases the lock on the child thread.
-        # - The child process returns.  Without the necessary fix, when the
-        #   main thread of the child process (which used to be the child thread
-        #   in the parent process) attempts to exit, it will try to acquire the
-        #   lock in the Thread._block Condition object and hang, because the
-        #   lock was held across the fork.
-
-        script = """if 1:
-            import os, time, threading
-
-            finish_join = False
-            start_fork = False
-
-            def worker():
-                # Wait until this thread's lock is acquired before forking to
-                # create the deadlock.
-                global finish_join
-                while not start_fork:
-                    time.sleep(0.01)
-                # LOCK HELD: Main thread holds lock across this call.
-                childpid = os.fork()
-                finish_join = True
-                if childpid != 0:
-                    # Parent process just waits for child.
-                    os.waitpid(childpid, 0)
-                # Child process should just return.
-
-            w = threading.Thread(target=worker)
-
-            # Stub out the private condition variable's lock acquire method.
-            # This acquires the lock and then waits until the child has forked
-            # before returning, which will release the lock soon after.  If
-            # someone else tries to fix this test case by acquiring this lock
-            # before forking instead of resetting it, the test case will
-            # deadlock when it shouldn't.
-            condition = w._block
-            orig_acquire = condition.acquire
-            call_count_lock = threading.Lock()
-            call_count = 0
-            def my_acquire():
-                global call_count
-                global start_fork
-                orig_acquire()  # LOCK ACQUIRED HERE
-                start_fork = True
-                if call_count == 0:
-                    while not finish_join:
-                        time.sleep(0.01)  # WORKER THREAD FORKS HERE
-                with call_count_lock:
-                    call_count += 1
-            condition.acquire = my_acquire
-
-            w.start()
-            w.join()
-            print('end of main')
-            """
-        self.assertScriptHasOutput(script, "end of main\n")
-
-    @unittest.skipUnless(hasattr(os, 'fork'), "needs os.fork()")
-    @unittest.skipIf(sys.platform in platforms_to_skip, "due to known OS bug")
-    def test_5_clear_waiter_locks_to_avoid_crash(self):
-        # Check that a spawned thread that forks doesn't segfault on certain
-        # platforms, namely OS X.  This used to happen if there was a waiter
-        # lock in the thread's condition variable's waiters list.  Even though
-        # we know the lock will be held across the fork, it is not safe to
-        # release locks held across forks on all platforms, so releasing the
-        # waiter lock caused a segfault on OS X.  Furthermore, since locks on
-        # OS X are (as of this writing) implemented with a mutex + condition
-        # variable instead of a semaphore, while we know that the Python-level
-        # lock will be acquired, we can't know if the internal mutex will be
-        # acquired at the time of the fork.
-
-        script = """if True:
-            import os, time, threading
-
-            start_fork = False
-
-            def worker():
-                # Wait until the main thread has attempted to join this thread
-                # before continuing.
-                while not start_fork:
-                    time.sleep(0.01)
-                childpid = os.fork()
-                if childpid != 0:
-                    # Parent process just waits for child.
-                    (cpid, rc) = os.waitpid(childpid, 0)
-                    assert cpid == childpid
-                    assert rc == 0
-                    print('end of worker thread')
-                else:
-                    # Child process should just return.
-                    pass
-
-            w = threading.Thread(target=worker)
-
-            # Stub out the private condition variable's _release_save method.
-            # This releases the condition's lock and flips the global that
-            # causes the worker to fork.  At this point, the problematic waiter
-            # lock has been acquired once by the waiter and has been put onto
-            # the waiters list.
-            condition = w._block
-            orig_release_save = condition._release_save
-            def my_release_save():
-                global start_fork
-                orig_release_save()
-                # Waiter lock held here, condition lock released.
-                start_fork = True
-            condition._release_save = my_release_save
-
-            w.start()
-            w.join()
-            print('end of main thread')
-            """
-        output = "end of worker thread\nend of main thread\n"
-        self.assertScriptHasOutput(script, output)
-
     @unittest.skipIf(sys.platform in platforms_to_skip, "due to known OS bug")
-    def test_6_daemon_threads(self):
+    def test_4_daemon_threads(self):
         # Check that a daemon thread cannot crash the interpreter on shutdown
         # by manipulating internal structures that are being disposed of in
         # the main thread.
@@ -867,6 +765,38 @@ class SubinterpThreadingTests(BaseTestCase):
         # The thread was joined properly.
         self.assertEqual(os.read(r, 1), b"x")
 
+    def test_threads_join_2(self):
+        # Same as above, but a delay gets introduced after the thread's
+        # Python code returned but before the thread state is deleted.
+        # To achieve this, we register a thread-local object which sleeps
+        # a bit when deallocated.
+        r, w = os.pipe()
+        self.addCleanup(os.close, r)
+        self.addCleanup(os.close, w)
+        code = r"""if 1:
+            import os
+            import threading
+            import time
+
+            class Sleeper:
+                def __del__(self):
+                    time.sleep(0.05)
+
+            tls = threading.local()
+
+            def f():
+                # Sleep a bit so that the thread is still running when
+                # Py_EndInterpreter is called.
+                time.sleep(0.05)
+                tls.x = Sleeper()
+                os.write(%d, b"x")
+            threading.Thread(target=f).start()
+            """ % (w,)
+        ret = _testcapi.run_in_subinterp(code)
+        self.assertEqual(ret, 0)
+        # The thread was joined properly.
+        self.assertEqual(os.read(r, 1), b"x")
+
     def test_daemon_threads_fatal_error(self):
         subinterp_code = r"""if 1:
             import os
diff --git a/Lib/threading.py b/Lib/threading.py
index b6d19d5..1921ee3 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -33,6 +33,7 @@ __all__ = ['active_count', 'Condition', 'current_thread', 'enumerate', 'Event',
 # Rename some stuff so "from threading import *" is safe
 _start_new_thread = _thread.start_new_thread
 _allocate_lock = _thread.allocate_lock
+_set_sentinel = _thread._set_sentinel
 get_ident = _thread.get_ident
 ThreadError = _thread.error
 try:
@@ -516,8 +517,6 @@ def _newname(template="Thread-%d"):
 _active_limbo_lock = _allocate_lock()
 _active = {}    # maps thread id to Thread object
 _limbo = {}
-
-# For debug and leak testing
 _dangling = WeakSet()
 
 # Main class for threads
@@ -548,28 +547,33 @@ class Thread:
         else:
             self._daemonic = current_thread().daemon
         self._ident = None
+        self._tstate_lock = None
         self._started = Event()
-        self._stopped = False
-        self._block = Condition(Lock())
+        self._is_stopped = False
         self._initialized = True
         # sys.stderr is not stored in the class like
         # sys.exc_info since it can be changed between instances
         self._stderr = _sys.stderr
+        # For debugging and _after_fork()
         _dangling.add(self)
 
-    def _reset_internal_locks(self):
+    def _reset_internal_locks(self, is_alive):
         # private!  Called by _after_fork() to reset our internal locks as
         # they may be in an invalid state leading to a deadlock or crash.
-        if hasattr(self, '_block'):  # DummyThread deletes _block
-            self._block.__init__()
         self._started._reset_internal_locks()
+        if is_alive:
+            self._set_tstate_lock()
+        else:
+            # The thread isn't alive after fork: it doesn't have a tstate
+            # anymore.
+            self._tstate_lock = None
 
     def __repr__(self):
         assert self._initialized, "Thread.__init__() was not called"
         status = "initial"
         if self._started.is_set():
             status = "started"
-        if self._stopped:
+        if self._is_stopped:
             status = "stopped"
         if self._daemonic:
             status += " daemon"
@@ -625,9 +629,18 @@ class Thread:
     def _set_ident(self):
         self._ident = get_ident()
 
+    def _set_tstate_lock(self):
+        """
+        Set a lock object which will be released by the interpreter when
+        the underlying thread state (see pystate.h) gets deleted.
+        """
+        self._tstate_lock = _set_sentinel()
+        self._tstate_lock.acquire()
+
     def _bootstrap_inner(self):
         try:
             self._set_ident()
+            self._set_tstate_lock()
             self._started.set()
             with _active_limbo_lock:
                 _active[self._ident] = self
@@ -682,7 +695,6 @@ class Thread:
                 pass
         finally:
             with _active_limbo_lock:
-                self._stop()
                 try:
                     # We don't call self._delete() because it also
                     # grabs _active_limbo_lock.
@@ -691,10 +703,8 @@ class Thread:
                     pass
 
     def _stop(self):
-        self._block.acquire()
-        self._stopped = True
-        self._block.notify_all()
-        self._block.release()
+        self._is_stopped = True
+        self._tstate_lock = None
 
     def _delete(self):
         "Remove current thread from the dict of currently running threads."
@@ -738,21 +748,24 @@ class Thread:
             raise RuntimeError("cannot join thread before it is started")
         if self is current_thread():
             raise RuntimeError("cannot join current thread")
-
-        self._block.acquire()
-        try:
-            if timeout is None:
-                while not self._stopped:
-                    self._block.wait()
-            else:
-                deadline = _time() + timeout
-                while not self._stopped:
-                    delay = deadline - _time()
-                    if delay <= 0:
-                        break
-                    self._block.wait(delay)
-        finally:
-            self._block.release()
+        if timeout is None:
+            self._wait_for_tstate_lock()
+        else:
+            self._wait_for_tstate_lock(timeout=timeout)
+
+    def _wait_for_tstate_lock(self, block=True, timeout=-1):
+        # Issue #18808: wait for the thread state to be gone.
+        # At the end of the thread's life, after all knowledge of the thread
+        # is removed from C data structures, C code releases our _tstate_lock.
+        # This method passes its arguments to _tstate_lock.aquire().
+        # If the lock is acquired, the C code is done, and self._stop() is
+        # called.  That sets ._is_stopped to True, and ._tstate_lock to None.
+        lock = self._tstate_lock
+        if lock is None:  # already determined that the C code is done
+            assert self._is_stopped
+        elif lock.acquire(block, timeout):
+            lock.release()
+            self._stop()
 
     @property
     def name(self):
@@ -771,7 +784,10 @@ class Thread:
 
     def is_alive(self):
         assert self._initialized, "Thread.__init__() not called"
-        return self._started.is_set() and not self._stopped
+        if self._is_stopped or not self._started.is_set():
+            return False
+        self._wait_for_tstate_lock(False)
+        return not self._is_stopped
 
     isAlive = is_alive
 
@@ -835,6 +851,7 @@ class _MainThread(Thread):
 
     def __init__(self):
         Thread.__init__(self, name="MainThread", daemon=False)
+        self._set_tstate_lock()
         self._started.set()
         self._set_ident()
         with _active_limbo_lock:
@@ -854,11 +871,6 @@ class _DummyThread(Thread):
     def __init__(self):
         Thread.__init__(self, name=_newname("Dummy-%d"), daemon=True)
 
-        # Thread._block consumes an OS-level locking primitive, which
-        # can never be used by a _DummyThread.  Since a _DummyThread
-        # instance is immortal, that's bad, so release this resource.
-        del self._block
-
         self._started.set()
         self._set_ident()
         with _active_limbo_lock:
@@ -904,6 +916,14 @@ from _thread import stack_size
 _main_thread = _MainThread()
 
 def _shutdown():
+    # Obscure:  other threads may be waiting to join _main_thread.  That's
+    # dubious, but some code does it.  We can't wait for C code to release
+    # the main thread's tstate_lock - that won't happen until the interpreter
+    # is nearly dead.  So we release it here.  Note that just calling _stop()
+    # isn't enough:  other threads may already be waiting on _tstate_lock.
+    assert _main_thread._tstate_lock is not None
+    assert _main_thread._tstate_lock.locked()
+    _main_thread._tstate_lock.release()
     _main_thread._stop()
     t = _pickSomeNonDaemonThread()
     while t:
@@ -949,18 +969,23 @@ def _after_fork():
     current = current_thread()
     _main_thread = current
     with _active_limbo_lock:
-        for thread in _enumerate():
+        # Dangling thread instances must still have their locks reset,
+        # because someone may join() them.
+        threads = set(_enumerate())
+        threads.update(_dangling)
+        for thread in threads:
             # Any lock/condition variable may be currently locked or in an
             # invalid state, so we reinitialize them.
-            thread._reset_internal_locks()
             if thread is current:
                 # There is only one active thread. We reset the ident to
                 # its new value since it can have changed.
+                thread._reset_internal_locks(True)
                 ident = get_ident()
                 thread._ident = ident
                 new_active[ident] = thread
             else:
                 # All the others are already stopped.
+                thread._reset_internal_locks(False)
                 thread._stop()
 
         _limbo.clear()
diff --git a/Lib/unittest/__init__.py b/Lib/unittest/__init__.py
index 201a3f0..a5d50af 100644
--- a/Lib/unittest/__init__.py
+++ b/Lib/unittest/__init__.py
@@ -11,7 +11,7 @@ Simple usage:
 
     import unittest
 
-    class IntegerArithmenticTestCase(unittest.TestCase):
+    class IntegerArithmeticTestCase(unittest.TestCase):
         def testAdd(self):  ## test method names begin 'test*'
             self.assertEqual((1 + 2), 3)
             self.assertEqual(0 + 1, 1)