[IronPython] IronPython 2.6.1 RC1, ctypes, and c_int.value

[Lepisto, Stephen P]

Thank you for your efforts with IronPython 2.6.1.  I am looking forward to the final product.

I was testing 2.6.1 RC1 to see if an issue I was having with v2.6.0 was fixed and I ran into an interesting problem with pyReadLine (v1.13), which I had installed under CPython v2.6.4.  A python-based program I am testing requires the readline module but I am getting an odd  error when readline is loaded.  The error is "SystemError: Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

I created a simple test case that shows the problem in action.  This test case runs fine under CPython v2.6.4 but fails under IronPython v2.6.1 RC1.  Please ignore the fact that it is really weird-looking code and not something that would normally be used.  The test case demonstrates the problem in as few lines as possible while exercising the same steps that readline uses (see the install_readline() function in readline's Console.py).

import ctypes
msvcrt = ctypes.cdll.LoadLibrary("msvcrt")
systemfn = ctypes.c_int.from_address(ctypes.addressof(msvcrt.system))
systemfn.value = ctypes.c_int.from_address(ctypes.addressof(msvcrt.system)).value

The last line triggers the error: "SystemError: Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

Apparently readline overwrites a function pointer ("PyOS_ReadlineFunctionPointer") inside the DLL that implements the sys module so that the line input functionality passes through the python readline module.  Since readline uses the sys.dllhandle to get access to the DLL and in IronPython v2.6.1 RC1 the sys.dllhandle is 0, I'm thinking the pyReadline package won't work on IronPython even if the above error is fixed.

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