Mercurial > hg
annotate tests/test-atomictempfile.py @ 14007:d764463b433e
atomictempfile: avoid infinite recursion in __del__().
The problem is that a programmer using atomictempfile directly can
make an innocent everyday mistake -- not enough args to the
constructor -- which escalates badly. You would expect a simple
TypeError crash in that case, but you actually get an infinite
recursion that is surprisingly difficult to kill: it happens between
__del__() and __getattr__(), and Python does not handle infinite
recursion from __del__() well.
The fix is to not implement __getattr__(), but instead assign instance
attributes for the methods we wish to delegate to the builtin file
type: write() and fileno(). I've audited mercurial.* and hgext.* and
found no users of atomictempfile using methods other than write() and
rename(). I audited third-party extensions and found one (snap)
passing an atomictempfile to util.fstat(), so I also threw in
fileno().
The last time I submitted a similar patch, Matt proposed that we make
atomictempfile a subclass of file instead of wrapping it. Rejected on
grounds of unnecessary complexity: for one thing, it would make the
Windows implementation of posixfile quite a bit more complex. It would
have to become a subclass of file rather than a simple function -- but
since it's written in C, this is non-obvious and non-trivial.
Furthermore, there's nothing wrong with wrapping objects and
delegating methods: it's a well-established pattern that works just
fine in many cases. Subclassing is not the answer to all of life's
problems.
author | Greg Ward <greg@gerg.ca> |
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date | Sun, 24 Apr 2011 19:25:10 -0400 |
parents | |
children | 774da7121fc9 |
rev | line source |
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14007
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atomictempfile: avoid infinite recursion in __del__().
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1 import os |
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2 import glob |
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3 from mercurial.util import atomictempfile |
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4 |
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5 # basic usage |
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6 def test1_simple(): |
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7 if os.path.exists('foo'): |
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8 os.remove('foo') |
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9 file = atomictempfile('foo') |
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10 (dir, basename) = os.path.split(file._tempname) |
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11 assert not os.path.isfile('foo') |
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12 assert basename in glob.glob('.foo-*') |
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13 |
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14 file.write('argh\n') |
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15 file.rename() |
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16 |
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17 assert os.path.isfile('foo') |
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18 assert basename not in glob.glob('.foo-*') |
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19 print 'OK' |
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20 |
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21 # close() removes the temp file but does not make the write |
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22 # permanent -- essentially discards your work (WTF?!) |
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23 def test2_close(): |
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24 if os.path.exists('foo'): |
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25 os.remove('foo') |
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26 file = atomictempfile('foo') |
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27 (dir, basename) = os.path.split(file._tempname) |
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28 |
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29 file.write('yo\n') |
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30 file.close() |
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31 |
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32 assert not os.path.isfile('foo') |
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33 assert basename not in os.listdir('.') |
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34 print 'OK' |
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35 |
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36 # if a programmer screws up and passes bad args to atomictempfile, they |
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37 # get a plain ordinary TypeError, not infinite recursion |
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38 def test3_oops(): |
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39 try: |
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40 file = atomictempfile() |
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41 except TypeError: |
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42 print "OK" |
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43 else: |
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44 print "expected TypeError" |
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45 |
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46 if __name__ == '__main__': |
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47 test1_simple() |
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48 test2_close() |
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49 test3_oops() |