[tahoe-lafs-trac-stream] [Tahoe-LAFS] #1531: use ctypes.get_last_error instead of GetLastError to access Windows error code

[Tahoe-LAFS]

#1531: use ctypes.get_last_error instead of GetLastError to access Windows error
code
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     Reporter:  davidsarah  |      Owner:  davidsarah
         Type:  defect      |     Status:  assigned
     Priority:  major       |  Milestone:  eventually
    Component:  code        |    Version:  1.9.0a1
   Resolution:              |   Keywords:  windows error GetLastError
Launchpad Bug:              |
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Old description:

> We have some code in [source:src/allmydata/windows/fixups.py] and
> [source:src/allmydata/util/fileutil.py] that calls Windows API functions,
> and then calls GetLastError if the API function fails. In theory, the
> Python interpreter could run code in-between on the same thread that
> changes the error code. See [http://bugs.python.org/issue1798].
>
> (We don't have any code in Tahoe proper that calls C runtime library
> functions, so this issue only affects us for GetLastError, not errno. It
> is somewhat less likely to happen with GetLastError than with errno, at
> least in CPython, but still possible.)

New description:

 We have some code in [source:src/allmydata/windows/fixups.py] and
 [source:src/allmydata/util/fileutil.py] that calls Windows API functions,
 and then calls GetLastError if the API function fails. In theory, the
 Python interpreter could run code in-between on the same thread that
 changes the error code. See [http://bugs.python.org/issue1798].

 (We don't have any code in Tahoe proper that calls C runtime library
 functions, so this issue only affects us for GetLastError, not errno. It
 is somewhat less likely to happen with GetLastError than with errno, at
 least in CPython, but still possible.)

--

Comment (by daira):

 Actually `fixups.py` never calls `GetLastError` (although perhaps it
 should).

--
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1531#comment:2>
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