diff options
Diffstat (limited to '.venv/lib/python3.12/site-packages/greenlet/tests/test_greenlet_trash.py')
| -rw-r--r-- | .venv/lib/python3.12/site-packages/greenlet/tests/test_greenlet_trash.py | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/.venv/lib/python3.12/site-packages/greenlet/tests/test_greenlet_trash.py b/.venv/lib/python3.12/site-packages/greenlet/tests/test_greenlet_trash.py new file mode 100644 index 00000000..c1fc1374 --- /dev/null +++ b/.venv/lib/python3.12/site-packages/greenlet/tests/test_greenlet_trash.py @@ -0,0 +1,187 @@ +# -*- coding: utf-8 -*- +""" +Tests for greenlets interacting with the CPython trash can API. + +The CPython trash can API is not designed to be re-entered from a +single thread. But this can happen using greenlets, if something +during the object deallocation process switches greenlets, and this second +greenlet then causes the trash can to get entered again. Here, we do this +very explicitly, but in other cases (like gevent) it could be arbitrarily more +complicated: for example, a weakref callback might try to acquire a lock that's +already held by another greenlet; that would allow a greenlet switch to occur. + +See https://github.com/gevent/gevent/issues/1909 + +This test is fragile and relies on details of the CPython +implementation (like most of the rest of this package): + + - We enter the trashcan and deferred deallocation after + ``_PyTrash_UNWIND_LEVEL`` calls. This constant, defined in + CPython's object.c, is generally 50. That's basically how many objects are required to + get us into the deferred deallocation situation. + + - The test fails by hitting an ``assert()`` in object.c; if the + build didn't enable assert, then we don't catch this. + + - If the test fails in that way, the interpreter crashes. +""" +from __future__ import print_function, absolute_import, division + +import unittest + + +class TestTrashCanReEnter(unittest.TestCase): + + def test_it(self): + try: + # pylint:disable-next=no-name-in-module + from greenlet._greenlet import get_tstate_trash_delete_nesting # pylint:disable=unused-import + except ImportError: + import sys + # Python 3.13 has not "trash delete nesting" anymore (but "delete later") + assert sys.version_info[:2] >= (3, 13) + self.skipTest("get_tstate_trash_delete_nesting is not available.") + + # Try several times to trigger it, because it isn't 100% + # reliable. + for _ in range(10): + self.check_it() + + def check_it(self): # pylint:disable=too-many-statements + import greenlet + from greenlet._greenlet import get_tstate_trash_delete_nesting # pylint:disable=no-name-in-module + main = greenlet.getcurrent() + + assert get_tstate_trash_delete_nesting() == 0 + + # We expect to be in deferred deallocation after this many + # deallocations have occurred. TODO: I wish we had a better way to do + # this --- that was before get_tstate_trash_delete_nesting; perhaps + # we can use that API to do better? + TRASH_UNWIND_LEVEL = 50 + # How many objects to put in a container; it's the container that + # queues objects for deferred deallocation. + OBJECTS_PER_CONTAINER = 500 + + class Dealloc: # define the class here because we alter class variables each time we run. + """ + An object with a ``__del__`` method. When it starts getting deallocated + from a deferred trash can run, it switches greenlets, allocates more objects + which then also go in the trash can. If we don't save state appropriately, + nesting gets out of order and we can crash the interpreter. + """ + + #: Has our deallocation actually run and switched greenlets? + #: When it does, this will be set to the current greenlet. This should + #: be happening in the main greenlet, so we check that down below. + SPAWNED = False + + #: Has the background greenlet run? + BG_RAN = False + + BG_GLET = None + + #: How many of these things have ever been allocated. + CREATED = 0 + + #: How many of these things have ever been deallocated. + DESTROYED = 0 + + #: How many were destroyed not in the main greenlet. There should always + #: be some. + #: If the test is broken or things change in the trashcan implementation, + #: this may not be correct. + DESTROYED_BG = 0 + + def __init__(self, sequence_number): + """ + :param sequence_number: The ordinal of this object during + one particular creation run. This is used to detect (guess, really) + when we have entered the trash can's deferred deallocation. + """ + self.i = sequence_number + Dealloc.CREATED += 1 + + def __del__(self): + if self.i == TRASH_UNWIND_LEVEL and not self.SPAWNED: + Dealloc.SPAWNED = greenlet.getcurrent() + other = Dealloc.BG_GLET = greenlet.greenlet(background_greenlet) + x = other.switch() + assert x == 42 + # It's important that we don't switch back to the greenlet, + # we leave it hanging there in an incomplete state. But we don't let it + # get collected, either. If we complete it now, while we're still + # in the scope of the initial trash can, things work out and we + # don't see the problem. We need this greenlet to complete + # at some point in the future, after we've exited this trash can invocation. + del other + elif self.i == 40 and greenlet.getcurrent() is not main: + Dealloc.BG_RAN = True + try: + main.switch(42) + except greenlet.GreenletExit as ex: + # We expect this; all references to us go away + # while we're still running, and we need to finish deleting + # ourself. + Dealloc.BG_RAN = type(ex) + del ex + + # Record the fact that we're dead last of all. This ensures that + # we actually get returned too. + Dealloc.DESTROYED += 1 + if greenlet.getcurrent() is not main: + Dealloc.DESTROYED_BG += 1 + + + def background_greenlet(): + # We direct through a second function, instead of + # directly calling ``make_some()``, so that we have complete + # control over when these objects are destroyed: we need them + # to be destroyed in the context of the background greenlet + t = make_some() + del t # Triggere deletion. + + def make_some(): + t = () + i = OBJECTS_PER_CONTAINER + while i: + # Nest the tuples; it's the recursion that gets us + # into trash. + t = (Dealloc(i), t) + i -= 1 + return t + + + some = make_some() + self.assertEqual(Dealloc.CREATED, OBJECTS_PER_CONTAINER) + self.assertEqual(Dealloc.DESTROYED, 0) + + # If we're going to crash, it should be on the following line. + # We only crash if ``assert()`` is enabled, of course. + del some + + # For non-debug builds of CPython, we won't crash. The best we can do is check + # the nesting level explicitly. + self.assertEqual(0, get_tstate_trash_delete_nesting()) + + # Discard this, raising GreenletExit into where it is waiting. + Dealloc.BG_GLET = None + # The same nesting level maintains. + self.assertEqual(0, get_tstate_trash_delete_nesting()) + + # We definitely cleaned some up in the background + self.assertGreater(Dealloc.DESTROYED_BG, 0) + + # Make sure all the cleanups happened. + self.assertIs(Dealloc.SPAWNED, main) + self.assertTrue(Dealloc.BG_RAN) + self.assertEqual(Dealloc.BG_RAN, greenlet.GreenletExit) + self.assertEqual(Dealloc.CREATED, Dealloc.DESTROYED ) + self.assertEqual(Dealloc.CREATED, OBJECTS_PER_CONTAINER * 2) + + import gc + gc.collect() + + +if __name__ == '__main__': + unittest.main() |