def setUp(self):
     # Set a very small check interval, this will make it more likely
     # that the interpreter crashes when threading is done incorrectly.
     if sys.version_info[:2] >= (3, 2):
         self._int = sys.getswitchinterval()
         sys.setswitchinterval(0.0000001)
     else:
         self._int = sys.getcheckinterval()
         sys.setcheckinterval(1)

    def test_trashcan_threads(self):
        # Issue #13992: trashcan mechanism should be thread-safe
        NESTING = 60
        N_THREADS = 2

        def sleeper_gen():
            """A generator that releases the GIL when closed or dealloc'ed."""
            try:
                yield
            finally:
                time.sleep(0.000001)

        class C(list):
            # Appending to a list is atomic, which avoids the use of a lock.
            inits = []
            dels = []
            def __init__(self, alist):
                self[:] = alist
                C.inits.append(None)
            def __del__(self):
                # This __del__ is called by subtype_dealloc().
                C.dels.append(None)
                # `g` will release the GIL when garbage-collected.  This
                # helps assert subtype_dealloc's behaviour when threads
                # switch in the middle of it.
                g = sleeper_gen()
                next(g)
                # Now that __del__ is finished, subtype_dealloc will proceed
                # to call list_dealloc, which also uses the trashcan mechanism.

        def make_nested():
            """Create a sufficiently nested container object so that the
            trashcan mechanism is invoked when deallocating it."""
            x = C([])
            for i in range(NESTING):
                x = [C([x])]
            del x

        def run_thread():
            """Exercise make_nested() in a loop."""
            while not exit:
                make_nested()

        old_switchinterval = sys.getswitchinterval()
        sys.setswitchinterval(1e-5)
        try:
            exit = []
            threads = []
            for i in range(N_THREADS):
                t = threading.Thread(target=run_thread)
                threads.append(t)
            with start_threads(threads, lambda: exit.append(1)):
                time.sleep(1.0)
        finally:
            sys.setswitchinterval(old_switchinterval)
        gc.collect()
        self.assertEqual(len(C.inits), len(C.dels))

 def tidy_up():
     """
     Put the bytecode back to how it was. Good as new.
     """
     if sys.version_info[0] < 3:
         sys.setcheckinterval(old_check_interval)
     else:
         sys.setswitchinterval(old_check_interval)
     for i in range(3):
         pb[where + i][0] = orig_bytes[i]

def release_priority_execution(p):
    sys.setcheckinterval(100)
    if sys.version_info > (3, 0, 0):
        sys.setswitchinterval(0.005)
    try:
        if platform.system() == "Windows":
            p.nice(psutil.NORMAL_PRIORITY_CLASS)
        else:
            p.nice(5)
    except psutil.AccessDenied:
        pass
    gc.enable()

def test_main():
    old_switchinterval = None
    try:
        old_switchinterval = sys.getswitchinterval()
        sys.setswitchinterval(1e-5)
    except AttributeError:
        pass
    try:
        run_unittest(ThreadedImportTests)
    finally:
        if old_switchinterval is not None:
            sys.setswitchinterval(old_switchinterval)

    def test_thread_safety_during_modification(self):
        hosts = range(100)
        policy = RoundRobinPolicy()
        policy.populate(None, hosts)

        errors = []

        def check_query_plan():
            try:
                for i in xrange(100):
                    list(policy.make_query_plan())
            except Exception as exc:
                errors.append(exc)

        def host_up():
            for i in xrange(1000):
                policy.on_up(randint(0, 99))

        def host_down():
            for i in xrange(1000):
                policy.on_down(randint(0, 99))

        threads = []
        for i in range(5):
            threads.append(Thread(target=check_query_plan))
            threads.append(Thread(target=host_up))
            threads.append(Thread(target=host_down))

        # make the GIL switch after every instruction, maximizing
        # the chance of race conditions
        check = six.PY2 or '__pypy__' in sys.builtin_module_names
        if check:
            original_interval = sys.getcheckinterval()
        else:
            original_interval = sys.getswitchinterval()

        try:
            if check:
                sys.setcheckinterval(0)
            else:
                sys.setswitchinterval(0.0001)
            map(lambda t: t.start(), threads)
            map(lambda t: t.join(), threads)
        finally:
            if check:
                sys.setcheckinterval(original_interval)
            else:
                sys.setswitchinterval(original_interval)

        if errors:
            self.fail("Saw errors: %s" % (errors,))

 def setUp(self):
     """
     Reduce the CPython check interval so that thread switches happen much
     more often, hopefully exercising more possible race conditions.  Also,
     delay actual test startup until the reactor has been started.
     """
     if _PY3:
         if getattr(sys, 'getswitchinterval', None) is not None:
             self.addCleanup(sys.setswitchinterval, sys.getswitchinterval())
             sys.setswitchinterval(0.0000001)
     else:
         if getattr(sys, 'getcheckinterval', None) is not None:
             self.addCleanup(sys.setcheckinterval, sys.getcheckinterval())
             sys.setcheckinterval(7)

def test_main():
    old_switchinterval = None
    # Issue #15599: FreeBSD/KVM cannot handle gil_interval == 1.
    new_switchinterval = 0.00001 if 'freebsd' in sys.platform else 0.00000001
    try:
        old_switchinterval = sys.getswitchinterval()
        sys.setswitchinterval(new_switchinterval)
    except AttributeError:
        pass
    try:
        run_unittest(ThreadedImportTests)
    finally:
        if old_switchinterval is not None:
            sys.setswitchinterval(old_switchinterval)

 def test_switchinterval(self):
     self.assertRaises(TypeError, sys.setswitchinterval)
     self.assertRaises(TypeError, sys.setswitchinterval, "a")
     self.assertRaises(ValueError, sys.setswitchinterval, -1.0)
     self.assertRaises(ValueError, sys.setswitchinterval, 0.0)
     orig = sys.getswitchinterval()
     # sanity check
     self.assertTrue(orig < 0.5, orig)
     try:
         for n in 0.00001, 0.05, 3.0, orig:
             sys.setswitchinterval(n)
             self.assertAlmostEqual(sys.getswitchinterval(), n)
     finally:
         sys.setswitchinterval(orig)

 def test_pending_calls_race(self):
     # Issue #14406: multi-threaded race condition when waiting on all
     # futures.
     event = threading.Event()
     def future_func():
         event.wait()
     oldswitchinterval = sys.getswitchinterval()
     sys.setswitchinterval(1e-6)
     try:
         fs = {self.executor.submit(future_func) for i in range(100)}
         event.set()
         futures.wait(fs, return_when=futures.ALL_COMPLETED)
     finally:
         sys.setswitchinterval(oldswitchinterval)

 def test_enumerate_after_join(self):
     # Try hard to trigger #1703448: a thread is still returned in
     # threading.enumerate() after it has been join()ed.
     enum = threading.enumerate
     old_interval = sys.getswitchinterval()
     try:
         for i in range(1, 100):
             sys.setswitchinterval(i * 0.0002)
             t = threading.Thread(target=lambda: None)
             t.start()
             t.join()
             l = enum()
             self.assertNotIn(t, l, "#1703448 triggered after %d trials: %s" % (i, l))
     finally:
         sys.setswitchinterval(old_interval)

def request_priority_execution():
    gc.disable()
    sys.setcheckinterval(999999999)
    if sys.version_info > (3, 0, 0):
        sys.setswitchinterval(1000)
    p = psutil.Process(os.getpid())
    try:
        if platform.system() == "Windows":
            p.nice(psutil.HIGH_PRIORITY_CLASS)
        else:
            p.nice(10)
    except psutil.AccessDenied:
        pass

    return p

    def test_lru_cache_threaded(self):
        n, m = 5, 11

        class C:

            def orig(self, x, y):
                return 3 * x + y

        instance = C()

        f = per_instance_lru_cache(maxsize=n*m)(C.orig)
        hits, misses, maxsize, currsize = f.cache_info(instance)
        self.assertEqual(currsize, 0)

        start = threading.Event()
        def full(k):
            start.wait(10)
            for _ in range(m):
                self.assertEqual(f(instance, k, 0), instance.orig(k, 0))

        def clear():
            start.wait(10)
            for _ in range(2*m):
                f.cache_clear(instance)

        orig_si = sys.getswitchinterval()
        sys.setswitchinterval(1e-6)
        try:
            # create n threads in order to fill cache
            threads = [threading.Thread(target=full, args=[k]) for k in range(n)]
            with support.start_threads(threads):
                start.set()

            hits, misses, maxsize, currsize = f.cache_info(instance)

            # XXX: Why can be not equal?
            self.assertLessEqual(misses, n)
            self.assertLessEqual(hits, m*n - misses)
            self.assertEqual(currsize, n)

            # create n threads in order to fill cache and 1 to clear it
            threads = [threading.Thread(target=clear)]
            threads += [threading.Thread(target=full, args=[k]) for k in range(n)]
            start.clear()
            with support.start_threads(threads):
                start.set()
        finally:
            sys.setswitchinterval(orig_si)

def setup_gil():
    """
    Set extremely long GIL release interval to let threads naturally progress
    through CPU-heavy sequences without forcing the wake of another thread that
    may contend trying to run the same CPU-heavy code. For the new-style work,
    this drops runtime ~33% and involuntary context switches by >80%,
    essentially making threads cooperatively scheduled.
    """
    try:
        # Python 2.
        sys.setcheckinterval(100000)
    except AttributeError:
        pass

    try:
        # Python 3.
        sys.setswitchinterval(10)
    except AttributeError:
        pass

    def adjust_balance_concurrently(self, account):
        def transact():
            account.deposit(5)
            time.sleep(0.001)
            account.withdraw(5)

        # Greatly improve the chance of an operation being interrupted
        # by thread switch, thus testing synchronization effectively
        try:
            sys.setswitchinterval(1e-12)
        except AttributeError:
            # For Python 2 compatibility
            sys.setcheckinterval(1)

        threads = [threading.Thread(target=transact) for _ in range(1000)]
        for thread in threads:
            thread.start()
        for thread in threads:
            thread.join()

    def test_is_alive_after_fork(self):
        # Try hard to trigger #18418: is_alive() could sometimes be True on
        # threads that vanished after a fork.
        old_interval = sys.getswitchinterval()
        self.addCleanup(sys.setswitchinterval, old_interval)

        # Make the bug more likely to manifest.
        sys.setswitchinterval(1e-6)

        for i in range(20):
            t = threading.Thread(target=lambda: None)
            t.start()
            self.addCleanup(t.join)
            pid = os.fork()
            if pid == 0:
                os._exit(1 if t.is_alive() else 0)
            else:
                pid, status = os.waitpid(pid, 0)
                self.assertEqual(0, status)

def frequent_thread_switches():
    """Make concurrency bugs more likely to manifest."""
    interval = None
    if not sys.platform.startswith('java'):
        if hasattr(sys, 'getswitchinterval'):
            interval = sys.getswitchinterval()
            sys.setswitchinterval(1e-6)
        else:
            interval = sys.getcheckinterval()
            sys.setcheckinterval(1)

    try:
        yield
    finally:
        if not sys.platform.startswith('java'):
            if hasattr(sys, 'setswitchinterval'):
                sys.setswitchinterval(interval)
            else:
                sys.setcheckinterval(interval)

def _inject_jump(self, where, dest):
    """
    Monkeypatch bytecode at ``where`` to force it to jump to ``dest``.

    Returns function which puts things back to how they were.
    """
    # We're about to do dangerous things to a function's code content.
    # We can't make a lock to prevent the interpreter from using those
    # bytes, so the best we can do is to set the check interval to be high
    # and just pray that this keeps other threads at bay.
    if sys.version_info[0] < 3:
        old_check_interval = sys.getcheckinterval()
        sys.setcheckinterval(2**20)
    else:
        old_check_interval = sys.getswitchinterval()
        sys.setswitchinterval(1000)

    pb = ctypes.pointer(self.ob_sval)
    orig_bytes = [pb[where + i][0] for i in range(3)]

    v = struct.pack("<BH", opcode.opmap["JUMP_ABSOLUTE"], dest)

    # Overwrite code to cause it to jump to the target
    if sys.version_info[0] < 3:
        for i in range(3):
            pb[where + i][0] = ord(v[i])
    else:
        for i in range(3):
            pb[where + i][0] = v[i]

    def tidy_up():
        """
        Put the bytecode back to how it was. Good as new.
        """
        if sys.version_info[0] < 3:
            sys.setcheckinterval(old_check_interval)
        else:
            sys.setswitchinterval(old_check_interval)
        for i in range(3):
            pb[where + i][0] = orig_bytes[i]

    return tidy_up

def lazy_client_trial(reset, target, test, get_client, use_greenlets):
    """Test concurrent operations on a lazily-connecting client.

    `reset` takes a collection and resets it for the next trial.

    `target` takes a lazily-connecting collection and an index from
    0 to NTHREADS, and performs some operation, e.g. an insert.

    `test` takes the lazily-connecting collection and asserts a
    post-condition to prove `target` succeeded.
    """
    if use_greenlets and not has_gevent:
        raise SkipTest('Gevent not installed')

    collection = MongoClient(host, port).pymongo_test.test

    # Make concurrency bugs more likely to manifest.
    interval = None
    if not sys.platform.startswith('java'):
        if sys.version_info >= (3, 2):
            interval = sys.getswitchinterval()
            sys.setswitchinterval(1e-6)
        else:
            interval = sys.getcheckinterval()
            sys.setcheckinterval(1)

    try:
        for i in range(NTRIALS):
            reset(collection)
            lazy_client = get_client(
                _connect=False, use_greenlets=use_greenlets)

            lazy_collection = lazy_client.pymongo_test.test
            run_threads(lazy_collection, target, use_greenlets)
            test(lazy_collection)

    finally:
        if not sys.platform.startswith('java'):
            if sys.version_info >= (3, 2):
                sys.setswitchinterval(interval)
            else:
                sys.setcheckinterval(interval)

    def trial(self, reset, target, test):
        """Test concurrent operations on a lazily-connecting client.

        `reset` takes a collection and resets it for the next trial.

        `target` takes a lazily-connecting collection and an index from
        0 to nthreads, and performs some operation, e.g. an insert.

        `test` takes a collection and asserts a post-condition to prove
        `target` succeeded.
        """
        if self.use_greenlets and not has_gevent:
            raise SkipTest("Gevent not installed")

        collection = self._get_client().pymongo_test.test

        # Make concurrency bugs more likely to manifest.
        if not sys.platform.startswith("java"):
            if PY3:
                self.interval = sys.getswitchinterval()
                sys.setswitchinterval(1e-6)
            else:
                self.interval = sys.getcheckinterval()
                sys.setcheckinterval(1)

        try:
            for i in range(self.ntrials):
                reset(collection)
                lazy_client = self._get_client(_connect=False, use_greenlets=self.use_greenlets)

                lazy_collection = lazy_client.pymongo_test.test
                self.run_threads(lazy_collection, target)
                test(collection)

        finally:
            if not sys.platform.startswith("java"):
                if PY3:
                    sys.setswitchinterval(self.interval)
                else:
                    sys.setcheckinterval(self.interval)