svn+ssh://pythondev@svn.python.org/python/trunk

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  r63977 | thomas.heller | 2008-06-06 10:33:46 +0200 (Fri, 06 Jun 2008) | 31 lines

  Issue #1798: Add ctypes calling convention that allows safe access of errno.

  ctypes maintains thread-local storage that has space for two error
  numbers: private copies of the system 'errno' value and, on Windows,
  the system error code accessed by the GetLastError() and
  SetLastError() api functions.

  Foreign functions created with CDLL(..., use_errno=True), when called,
  swap the system 'errno' value with the private copy just before the
  actual function call, and swapped again immediately afterwards.  The
  'use_errno' parameter defaults to False, in this case 'ctypes_errno'
  is not touched.

  On Windows, foreign functions created with CDLL(...,
  use_last_error=True) or WinDLL(..., use_last_error=True) swap the
  system LastError value with the ctypes private copy.

  The values are also swapped immeditately before and after ctypes
  callback functions are called, if the callbacks are constructed using
  the new optional use_errno parameter set to True: CFUNCTYPE(...,
  use_errno=TRUE) or WINFUNCTYPE(..., use_errno=True).

  New ctypes functions are provided to access the ctypes private copies
  from Python:

  - ctypes.set_errno(value) and ctypes.set_last_error(value) store
    'value' in the private copy and returns the previous value.

  - ctypes.get_errno() and ctypes.get_last_error() returns the current
    ctypes private copies value.
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