[Python-Dev] [Python-checkins] Python Regression Test Failures refleak (1)

[Tim Peters]

[Tim, gets different results across whole runs of
     python_d  ../Lib/test/regrtest.py -R 2:40: test_filecmp test_exceptions
]

I think I found the cause for test_filecmp giving different results
across runs, at least on Windows.  It appears to be due to this test
line:

        self.failUnless(d.same_files == ['file'])

and you _still_ think I'm nuts ;-)  The skinny is that

        d = filecmp.dircmp(self.dir, self.dir_same)

and filecmp contains a module-level _cache with a funky scheme for
avoiding file comparisons if various os.stat() values haven't changed.
 But st_mtime on Windows doesn't necessarily change when a file is
modified -- it has limited resolution (2 seconds on FAT32, and I'm
having a hard time finding a believable answer for NTFS (which I'm
using)).

In any case, filecmp._cache _usually_ doesn't change during a run, but
sometimes it sprouts a new entry, like

 {('c:\\docume~1\\owner\\locals~1\\temp\\dir\\file',
   'c:\\docume~1\\owner\\locals~1\\temp\\dir-same\\file'):
     ((32768, 27L, 1149640843.78125),
      (32768, 27L, 1149640843.796875),
      True)
 }

and then that shows up as a small "leak".

That's easily repaired, and after doing so I haven't seen test_filecmp
report a leak again.

test_exceptions is a different story.  My first 12 post-fix runs of:

    python_d ..\Lib\test\regrtest.py -R2:40: test_filecmp test_exceptions

gave leak-free:

    test_filecmp
    beginning 42 repetitions
    123456789012345678901234567890123456789012
    ..........................................
    test_exceptions
    beginning 42 repetitions
    123456789012345678901234567890123456789012
    ..........................................
    All 2 tests OK.
    [25878 refs]

output, but the 13th was unlucky:

    test_filecmp
    beginning 42 repetitions
    123456789012345678901234567890123456789012
    ..........................................
    test_exceptions
    beginning 42 repetitions
    123456789012345678901234567890123456789012
    ..........................................
    test_exceptions leaked [0, 203, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
       0, 0, 0, 0, 0] references
    All 2 tests OK.
    [25883 refs]

Running test_filecmp too isn't necessary for me to see this --
test_exceptions can be run by itself, although it typically takes me
about 15 runs before "a leak" is reported.  When a leak is reported,
it's always 203, and there's only one of those in the leak vector, but
I've seen it at index positions 0, 1, 2, and 3 (i.e., it moves around;
it was at index 1 in the output above).

Anyone bored enough to report what happens on Linux?  Anyone remember
adding a goofy cache to exception internals?

a-suitable-msg-for-6/6/6-ly y'rs  - tim