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.

2 files changed, 125 insertions, 23 deletions

diff --git a/Lib/ctypes/__init__.py b/Lib/ctypes/__init__.py
index 41d39dc..d3e11dc 100644
--- a/Lib/ctypes/__init__.py
+++ b/Lib/ctypes/__init__.py
@@ -33,7 +33,9 @@ if _os.name == "posix" and _sys.platform == "darwin":
         DEFAULT_MODE = RTLD_GLOBAL
 
 from _ctypes import FUNCFLAG_CDECL as _FUNCFLAG_CDECL, \
-     FUNCFLAG_PYTHONAPI as _FUNCFLAG_PYTHONAPI
+     FUNCFLAG_PYTHONAPI as _FUNCFLAG_PYTHONAPI, \
+     FUNCFLAG_USE_ERRNO as _FUNCFLAG_USE_ERRNO, \
+     FUNCFLAG_USE_LASTERROR as _FUNCFLAG_USE_LASTERROR
 
 """
 WINOLEAPI -> HRESULT
@@ -73,8 +75,9 @@ def c_buffer(init, size=None):
     return create_string_buffer(init, size)
 
 _c_functype_cache = {}
-def CFUNCTYPE(restype, *argtypes):
-    """CFUNCTYPE(restype, *argtypes) -> function prototype.
+def CFUNCTYPE(restype, *argtypes, **kw):
+    """CFUNCTYPE(restype, *argtypes,
+                 use_errno=False, use_last_error=False) -> function prototype.
 
     restype: the result type
     argtypes: a sequence specifying the argument types
@@ -88,14 +91,21 @@ def CFUNCTYPE(restype, *argtypes):
     prototype((ordinal number, dll object)[, paramflags]) -> foreign function exported by ordinal
     prototype((function name, dll object)[, paramflags]) -> foreign function exported by name
     """
+    flags = _FUNCFLAG_CDECL
+    if kw.pop("use_errno", False):
+        flags |= _FUNCFLAG_USE_ERRNO
+    if kw.pop("use_last_error", False):
+        flags |= _FUNCFLAG_USE_LASTERROR
+    if kw:
+        raise ValueError("unexpected keyword argument(s) %s" % kw.keys())
     try:
-        return _c_functype_cache[(restype, argtypes)]
+        return _c_functype_cache[(restype, argtypes, flags)]
     except KeyError:
         class CFunctionType(_CFuncPtr):
             _argtypes_ = argtypes
             _restype_ = restype
-            _flags_ = _FUNCFLAG_CDECL
-        _c_functype_cache[(restype, argtypes)] = CFunctionType
+            _flags_ = flags
+        _c_functype_cache[(restype, argtypes, flags)] = CFunctionType
         return CFunctionType
 
 if _os.name in ("nt", "ce"):
@@ -106,16 +116,23 @@ if _os.name in ("nt", "ce"):
         _FUNCFLAG_STDCALL = _FUNCFLAG_CDECL
 
     _win_functype_cache = {}
-    def WINFUNCTYPE(restype, *argtypes):
+    def WINFUNCTYPE(restype, *argtypes, **kw):
         # docstring set later (very similar to CFUNCTYPE.__doc__)
+        flags = _FUNCFLAG_STDCALL
+        if kw.pop("use_errno", False):
+            flags |= _FUNCFLAG_USE_ERRNO
+        if kw.pop("use_last_error", False):
+            flags |= _FUNCFLAG_USE_LASTERROR
+        if kw:
+            raise ValueError("unexpected keyword argument(s) %s" % kw.keys())
         try:
-            return _win_functype_cache[(restype, argtypes)]
+            return _win_functype_cache[(restype, argtypes, flags)]
         except KeyError:
             class WinFunctionType(_CFuncPtr):
                 _argtypes_ = argtypes
                 _restype_ = restype
-                _flags_ = _FUNCFLAG_STDCALL
-            _win_functype_cache[(restype, argtypes)] = WinFunctionType
+                _flags_ = flags
+            _win_functype_cache[(restype, argtypes, flags)] = WinFunctionType
             return WinFunctionType
     if WINFUNCTYPE.__doc__:
         WINFUNCTYPE.__doc__ = CFUNCTYPE.__doc__.replace("CFUNCTYPE", "WINFUNCTYPE")
@@ -124,6 +141,7 @@ elif _os.name == "posix":
     from _ctypes import dlopen as _dlopen
 
 from _ctypes import sizeof, byref, addressof, alignment, resize
+from _ctypes import get_errno, set_errno
 from _ctypes import _SimpleCData
 
 def _check_size(typ, typecode=None):
@@ -313,12 +331,24 @@ class CDLL(object):
     Calling the functions releases the Python GIL during the call and
     reacquires it afterwards.
     """
-    class _FuncPtr(_CFuncPtr):
-        _flags_ = _FUNCFLAG_CDECL
-        _restype_ = c_int # default, can be overridden in instances
+    _func_flags_ = _FUNCFLAG_CDECL
+    _func_restype_ = c_int
 
-    def __init__(self, name, mode=DEFAULT_MODE, handle=None):
+    def __init__(self, name, mode=DEFAULT_MODE, handle=None,
+                 use_errno=False,
+                 use_last_error=False):
         self._name = name
+        flags = self._func_flags_
+        if use_errno:
+            flags |= _FUNCFLAG_USE_ERRNO
+        if use_last_error:
+            flags |= _FUNCFLAG_USE_LASTERROR
+
+        class _FuncPtr(_CFuncPtr):
+            _flags_ = flags
+            _restype_ = self._func_restype_
+        self._FuncPtr = _FuncPtr
+
         if handle is None:
             self._handle = _dlopen(self._name, mode)
         else:
@@ -348,9 +378,7 @@ class PyDLL(CDLL):
     access Python API functions.  The GIL is not released, and
     Python exceptions are handled correctly.
     """
-    class _FuncPtr(_CFuncPtr):
-        _flags_ = _FUNCFLAG_CDECL | _FUNCFLAG_PYTHONAPI
-        _restype_ = c_int # default, can be overridden in instances
+    _func_flags_ = _FUNCFLAG_CDECL | _FUNCFLAG_PYTHONAPI
 
 if _os.name in ("nt", "ce"):
 
@@ -358,9 +386,7 @@ if _os.name in ("nt", "ce"):
         """This class represents a dll exporting functions using the
         Windows stdcall calling convention.
         """
-        class _FuncPtr(_CFuncPtr):
-            _flags_ = _FUNCFLAG_STDCALL
-            _restype_ = c_int # default, can be overridden in instances
+        _func_flags_ = _FUNCFLAG_STDCALL
 
     # XXX Hm, what about HRESULT as normal parameter?
     # Mustn't it derive from c_long then?
@@ -384,9 +410,8 @@ if _os.name in ("nt", "ce"):
         HRESULT error values are automatically raised as WindowsError
         exceptions.
         """
-        class _FuncPtr(_CFuncPtr):
-            _flags_ = _FUNCFLAG_STDCALL
-            _restype_ = HRESULT
+        _func_flags_ = _FUNCFLAG_STDCALL
+        _func_restype_ = HRESULT
 
 class LibraryLoader(object):
     def __init__(self, dlltype):
@@ -424,6 +449,7 @@ if _os.name in ("nt", "ce"):
         GetLastError = windll.kernel32.GetLastError
     else:
         GetLastError = windll.coredll.GetLastError
+    from _ctypes import get_last_error, set_last_error
 
     def WinError(code=None, descr=None):
         if code is None:
diff --git a/Lib/ctypes/test/test_errno.py b/Lib/ctypes/test/test_errno.py
new file mode 100644
index 0000000..ce1cfad
--- /dev/null
+++ b/Lib/ctypes/test/test_errno.py
@@ -0,0 +1,76 @@
+import unittest, os, errno

+from ctypes import *

+from ctypes.util import find_library

+import threading

+

+class Test(unittest.TestCase):

+    def test_open(self):

+        libc_name = find_library("c")

+        if libc_name is not None:

+            libc = CDLL(libc_name, use_errno=True)

+            if os.name == "nt":

+                libc_open = libc._open

+            else:

+                libc_open = libc.open

+

+            libc_open.argtypes = c_char_p, c_int

+

+            self.failUnlessEqual(libc_open("", 0), -1)

+            self.failUnlessEqual(get_errno(), errno.ENOENT)

+

+            self.failUnlessEqual(set_errno(32), errno.ENOENT)

+            self.failUnlessEqual(get_errno(), 32)

+

+

+            def _worker():

+                set_errno(0)

+

+                libc = CDLL(libc_name, use_errno=False)

+                if os.name == "nt":

+                    libc_open = libc._open

+                else:

+                    libc_open = libc.open

+                libc_open.argtypes = c_char_p, c_int

+                self.failUnlessEqual(libc_open("", 0), -1)

+                self.failUnlessEqual(get_errno(), 0)

+

+            t = threading.Thread(target=_worker)

+            t.start()

+            t.join()

+

+            self.failUnlessEqual(get_errno(), 32)

+            set_errno(0)

+

+    if os.name == "nt":

+

+        def test_GetLastError(self):

+            dll = WinDLL("kernel32", use_last_error=True)

+            GetModuleHandle = dll.GetModuleHandleA

+            GetModuleHandle.argtypes = [c_wchar_p]

+

+            self.failUnlessEqual(0, GetModuleHandle("foo"))

+            self.failUnlessEqual(get_last_error(), 126)

+

+            self.failUnlessEqual(set_last_error(32), 126)

+            self.failUnlessEqual(get_last_error(), 32)

+

+            def _worker():

+                set_last_error(0)

+

+                dll = WinDLL("kernel32", use_last_error=False)

+                GetModuleHandle = dll.GetModuleHandleW

+                GetModuleHandle.argtypes = [c_wchar_p]

+                GetModuleHandle("bar")

+

+                self.failUnlessEqual(get_last_error(), 0)

+

+            t = threading.Thread(target=_worker)

+            t.start()

+            t.join()

+

+            self.failUnlessEqual(get_last_error(), 32)

+

+            set_last_error(0)

+

+if __name__ == "__main__":

+    unittest.main()