cpython: b3c2472c12a1 (original) (raw)

Mercurial > cpython

changeset 88637:b3c2472c12a1 3.3

Issue #20317: Don't create a reference loop in ExitStack [#20317]

Nick Coghlan ncoghlan@gmail.com
date	Wed, 22 Jan 2014 22:24:46 +1000
parents	1b89fd73c625
children	46c3ea358784 b26db63bb931
files	Lib/contextlib.py Lib/test/test_contextlib.py Misc/NEWS
diffstat	3 files changed, 38 insertions(+), 1 deletions(-)[+] [-] Lib/contextlib.py 10 Lib/test/test_contextlib.py 23 Misc/NEWS 6

line wrap: on

line diff

--- a/Lib/contextlib.py +++ b/Lib/contextlib.py @@ -231,11 +231,19 @@ class ExitStack(object): # we were actually nesting multiple with statements frame_exc = sys.exc_info()[1] def _fix_exception_context(new_exc, old_exc):

       # Context isn't what we want, so find the end of the chain[](#l1.7)
       while 1:[](#l1.8)
           exc_context = new_exc.__context__[](#l1.9)

           if exc_context in (None, frame_exc):[](#l1.10)

           if exc_context is old_exc:[](#l1.11)

               # Context is already set correctly (see issue 20317)[](#l1.12)

```
               return[](#l1.13)
```

           if exc_context is None or exc_context is frame_exc:[](#l1.14)
               break[](#l1.15)

           details = id(new_exc), id(old_exc), id(exc_context)[](#l1.16)

           raise Exception(str(details))[](#l1.17)
           new_exc = exc_context[](#l1.18)

       # Change the end of the chain to point to the exception[](#l1.19)

       # we expect it to reference[](#l1.20)
       new_exc.__context__ = old_exc[](#l1.21)

# Callbacks are invoked in LIFO order to match the behaviour of

--- a/Lib/test/test_contextlib.py +++ b/Lib/test/test_contextlib.py @@ -600,6 +600,29 @@ class TestExitStack(unittest.TestCase): else: self.fail("Expected KeyError, but no exception was raised")

def test_exit_exception_with_correct_context(self):

   # http://bugs.python.org/issue20317[](#l2.8)

```
   @contextmanager[](#l2.9)
```

   def gets_the_context_right():[](#l2.10)

```
       try:[](#l2.11)
```
```
           yield 6[](#l2.12)
```
```
       finally:[](#l2.13)
```
```
           1 / 0[](#l2.14)
```

   # The contextmanager already fixes the context, so prior to the[](#l2.16)

   # fix, ExitStack would try to fix it *again* and get into an[](#l2.17)

   # infinite self-referential loop[](#l2.18)

```
   try:[](#l2.19)
```

       with ExitStack() as stack:[](#l2.20)

           stack.enter_context(gets_the_context_right())[](#l2.21)

           stack.enter_context(gets_the_context_right())[](#l2.22)

           stack.enter_context(gets_the_context_right())[](#l2.23)

   except ZeroDivisionError as exc:[](#l2.24)

       self.assertIsInstance(exc.__context__, ZeroDivisionError)[](#l2.25)

       self.assertIsInstance(exc.__context__.__context__, ZeroDivisionError)[](#l2.26)

       self.assertIsNone(exc.__context__.__context__.__context__)[](#l2.27)

+ + def test_body_exception_suppress(self): def suppress_exc(*exc_details): return True

--- a/Misc/NEWS +++ b/Misc/NEWS @@ -50,6 +50,12 @@ Core and Builtins Library ------- +- Issue #20317: ExitStack.exit could create a self-referential loop if an

exception raised by a cleanup operation already had its context set
correctly (for example, by the @contextmanager decorator). The infinite
loop this caused is now avoided by checking if the expected context is
already set before trying to fix it. +

Issue #20311: select.epoll.poll() now rounds the timeout away from zero, instead of rounding towards zero. For example, a timeout of one microsecond is now rounded to one millisecond, instead of being rounded to zero.