8000 Incorrect marshalling of string in Py_SetPythonHome · Issue #179 · pythonnet/pythonnet · GitHub
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leomeuk opened this issue Mar 8, 2016 · 3 comments · Fixed by #415
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Incorrect marshalling of string in Py_SetPythonHome #179

leomeuk opened this issue Mar 8, 2016 · 3 comments · Fixed by #415

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@leomeuk
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leomeuk commented Mar 8, 2016

I noticed that when PythonEngine.PythonHome was set and a subsequent Initialize() call was made my .Net application would close unexpectedly.

It looks like the call to Py_SetPythonHome made in runtime.cs is implicitly marshalling the string to a char array for the unmanaged code. My suspicion is that the Python sourcecode is keeping a record of the pointer rather than making a copy of the data. The managed runtime will free the memory allocated to char array as soon as the function finishes executing leaving a dangling pointer. This then leads to the unexpected Initialize() behaviour.

[DllImport(Runtime.dll, CallingConvention = CallingConvention.Cdecl,
    ExactSpelling = true, CharSet = CharSet.Ansi)]
internal unsafe static extern void
Py_SetPythonHome(string home);

The solution appears to be to explicitly marshal the string and hang onto the pointer until it is no longer needed, i.e.

[DllImport(Runtime.dll, CallingConvention = CallingConvention.Cdecl,
     ExactSpelling = true, CharSet = CharSet.Ansi)]
internal unsafe static extern void
Py_SetPythonHome(IntPtr home);

IntPtr str = Marshal.StringToHGlobalAnsi(@"C:\Python27");
Py_SetPythonHome(str);
// do stuff
Marshal.FreeHGlobal(str);

Running Win7, .Net4.5 and Python 2.7.11.
@den-run-ai
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@leomeuk looks like you are correct - I tested this crash in csi:

Microsoft (R) Roslyn C# Compiler version 1.1.0.51204
Loading context from 'CSharpInteractive.rsp'.
Type "#help" for more information.
> #r "C:\Python\Python27\Lib\site-packages\Python.Runtime.dll"
> using Python.Runtime;
> PythonEngine.PythonHome = @"C:\Python\Python27";
> PythonEngine.Initialize();
> PythonEngine.PythonHome
Hosting process exited with exit code -1073740940.
Loading context from 'CSharpInteractive.rsp'.

@den-run-ai
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@leomeuk can you submit a patch and corresponding unit test?

@leomeuk
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leomeuk commented Mar 12, 2016

@denfromufa I'll look at doing so this weekend.

@leomeuk leomeuk mentioned this issue Mar 13, 2016
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@den-run-ai den-run-ai mentioned this issue Sep 7, 2016
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@vmuriart vmuriart mentioned this issue Mar 3, 2017
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Fix set pythonhome vmuriart/pythonnet
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@leomeuk @den-run-ai
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