[issue34157] NamedTemporaryFile can leave temporary files behind

[Giampaolo Rodola']

Change by Giampaolo Rodola' :


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nosy: +giampaolo.rodola

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[issue34157] NamedTemporaryFile can leave temporary files behind

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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nosy: +xtreak

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[issue34157] NamedTemporaryFile can leave temporary files behind

[R. David Murray]

Change by R. David Murray :


--
resolution: duplicate -> 
stage: resolved -> needs patch
status: closed -> open

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[issue34157] NamedTemporaryFile can leave temporary files behind

[R. David Murray]

R. David Murray  added the comment:

Nick, what Jakub is saying is that 'with' hasn't even gotten involved yet: 
we're still executing the NamedTemporaryFile constructor, so the object hasn't 
been returned for 'with' to operate on yet.  In other words, 
NamedTemporaryFile.__init__ isn't safe against ctl-C when it calls _mkstemp, 
which is obvious by inspection since it isn't inside the try/except.

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nosy: +r.david.murray

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[issue34157] NamedTemporaryFile can leave temporary files behind

[Nick Coghlan]

Nick Coghlan  added the comment:

It's still the same problem - the underlying issue is that the with statement 
machinery doesn't currently mask signals in the main thread while __enter__ and 
__exit__ are running, so __enter__ and __exit__ methods written in Python are 
also at risk of being interrupted at an inopportune point.

This means that even "with closing(open('filename')) as f: ..." is more at risk 
of leaving the file open until __del__ cleans it up than the version that calls 
open() directly.

So if this a concern that an application needs to worry about, then it 
currently needs to adopt a more complicated execution structure where:

1. The main thread launches a subthread that actually does all the work.
2. The main thread immediately drops into "active_thread.join()" (which can be 
interrupted by Ctrl-C)

Unfortunately, this scheme *doesn't* work for applications where the 
application itself needs to detect and handling signals other than Ctrl-C.

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[issue34157] NamedTemporaryFile can leave temporary files behind

[Jakub Wilk]

Jakub Wilk  added the comment:

I think issue29988 is unrelated, or at least not the whole story.

These are samples of tracebacks I see when the file is left behind:

  Traceback (most recent call last):
File "test-tmpfile.py", line 4, in 
  with tempfile.NamedTemporaryFile(dir='.'):
File "/opt/python/lib/python3.8/tempfile.py", line 548, in 
NamedTemporaryFile
  (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags, output_type)
File "/opt/python/lib/python3.8/tempfile.py", line 258, in _mkstemp_inner
  fd = _os.open(file, flags, 0o600)
  KeyboardInterrupt
  
  Traceback (most recent call last):
File "test-tmpfile.py", line 4, in 
  with tempfile.NamedTemporaryFile(dir='.'):
File "/opt/python/lib/python3.8/tempfile.py", line 548, in 
NamedTemporaryFile
  (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags, output_type)
File "/opt/python/lib/python3.8/tempfile.py", line 269, in _mkstemp_inner
  return (fd, _os.path.abspath(file))
File "/opt/python/lib/python3.8/posixpath.py", line 371, in abspath
  path = os.fspath(path)
  KeyboardInterrupt
  
  Traceback (most recent call last):
File "test-tmpfile.py", line 4, in 
  with tempfile.NamedTemporaryFile(dir='.'):
File "/opt/python/lib/python3.8/tempfile.py", line 548, in 
NamedTemporaryFile
  (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags, output_type)
File "/opt/python/lib/python3.8/tempfile.py", line 269, in _mkstemp_inner
  return (fd, _os.path.abspath(file))
File "/opt/python/lib/python3.8/posixpath.py", line 378, in abspath
  return normpath(path)
File "/opt/python/lib/python3.8/posixpath.py", line 355, in normpath
  if comp in (empty, dot):
  KeyboardInterrupt

In all cases the interrupt happened in the NamedTemporaryFile function,
so before __enter__/__exit__ would have chance to do its job.

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[issue34157] NamedTemporaryFile can leave temporary files behind

[Nick Coghlan]

Nick Coghlan  added the comment:

Aye, this is a specific case of the general issue noted in 
https://bugs.python.org/issue29988 (while it may be partially mitigated by 
https://bugs.python.org/issue32949, it isn't a guarantee)

--
resolution:  -> duplicate
stage:  -> resolved
status: open -> closed
superseder:  -> with statements are not ensuring that __exit__ is called if 
__enter__ succeeds

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[issue34157] NamedTemporaryFile can leave temporary files behind

[Raymond Hettinger]

Raymond Hettinger  added the comment:

Nick, is this related to the bug where the "finally" portion of a context 
manager isn't guaranteed to be called?

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nosy: +ncoghlan, rhettinger

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[issue34157] NamedTemporaryFile can leave temporary files behind

[Jakub Wilk]

New submission from Jakub Wilk :

If you press Ctrl+C at the wrong moment, NamedTemporaryFile won't delete the
temporary file. To reproduce, you can try this script:

import tempfile
while True:
with tempfile.NamedTemporaryFile(dir='.'):
pass

I get a stray temporary file when I press Ctrl+C about 40% of the time.

--
components: Library (Lib)
messages: 321965
nosy: jwilk
priority: normal
severity: normal
status: open
title: NamedTemporaryFile can leave temporary files behind
type: behavior
versions: Python 3.8

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