On Windows, use the Python 'Activation Context' when loading extensions

to avoid problems loading the CRT from a private assembly.  Via bug 4566.

PC/dl_nt.c

@@ -18,6 +18,63 @@ char dllVersionBuffer[16] = ""; // a private buffer
 HMODULE PyWin_DLLhModule = NULL;
 const char *PyWin_DLLVersionString = dllVersionBuffer;
 
+// Windows "Activation Context" work:
+// Our .pyd extension modules are generally built without a manifest (ie,
+// those included with Python and those built with a default distutils.
+// This requires we perform some "activation context" magic when loading our
+// extensions.  In summary:
+// * As our DLL loads we save the context being used.
+// * Before loading our extensions we re-activate our saved context.
+// * After extension load is complete we restore the old context.
+// As an added complication, this magic only works on XP or later - we simply
+// use the existence (or not) of the relevant function pointers from kernel32.
+// See bug 4566 (http://python.org/sf/4566) for more details.
+
+typedef BOOL (WINAPI * PFN_GETCURRENTACTCTX)(HANDLE *);
+typedef BOOL (WINAPI * PFN_ACTIVATEACTCTX)(HANDLE, ULONG_PTR *);
+typedef BOOL (WINAPI * PFN_DEACTIVATEACTCTX)(DWORD, ULONG_PTR);
+typedef BOOL (WINAPI * PFN_ADDREFACTCTX)(HANDLE);
+typedef BOOL (WINAPI * PFN_RELEASEACTCTX)(HANDLE);
+
+// locals and function pointers for this activation context magic.
+static HANDLE PyWin_DLLhActivationContext = NULL; // one day it might be public
+static PFN_GETCURRENTACTCTX pfnGetCurrentActCtx = NULL;
+static PFN_ACTIVATEACTCTX pfnActivateActCtx = NULL;
+static PFN_DEACTIVATEACTCTX pfnDeactivateActCtx = NULL;
+static PFN_ADDREFACTCTX pfnAddRefActCtx = NULL;
+static PFN_RELEASEACTCTX pfnReleaseActCtx = NULL;
+
+void _LoadActCtxPointers()
+{
+	HINSTANCE hKernel32 = GetModuleHandleW(L"kernel32.dll");
+	if (hKernel32)
+		pfnGetCurrentActCtx = (PFN_GETCURRENTACTCTX) GetProcAddress(hKernel32, "GetCurrentActCtx");
+	// If we can't load GetCurrentActCtx (ie, pre XP) , don't bother with the rest.
+	if (pfnGetCurrentActCtx) {
+		pfnActivateActCtx = (PFN_ACTIVATEACTCTX) GetProcAddress(hKernel32, "ActivateActCtx");
+		pfnDeactivateActCtx = (PFN_DEACTIVATEACTCTX) GetProcAddress(hKernel32, "DeactivateActCtx");
+		pfnAddRefActCtx = (PFN_ADDREFACTCTX) GetProcAddress(hKernel32, "AddRefActCtx");
+		pfnReleaseActCtx = (PFN_RELEASEACTCTX) GetProcAddress(hKernel32, "ReleaseActCtx");
+	}
+}
+
+ULONG_PTR _Py_ActivateActCtx()
+{
+	ULONG_PTR ret = 0;
+	if (PyWin_DLLhActivationContext && pfnActivateActCtx)
+		if (!(*pfnActivateActCtx)(PyWin_DLLhActivationContext, &ret)) {
+			OutputDebugString("Python failed to activate the activation context before loading a DLL\n");
+			ret = 0; // no promise the failing function didn't change it!
+		}
+	return ret;
+}
+
+void _Py_DeactivateActCtx(ULONG_PTR cookie)
+{
+	if (cookie && pfnDeactivateActCtx)
+		if (!(*pfnDeactivateActCtx)(0, cookie))
+			OutputDebugString("Python failed to de-activate the activation context\n");
+}
 
 BOOL	WINAPI	DllMain (HANDLE hInst, 
 						ULONG ul_reason_for_call,
@@ -29,9 +86,18 @@ BOOL	WINAPI	DllMain (HANDLE hInst,
 			PyWin_DLLhModule = hInst;
 			// 1000 is a magic number I picked out of the air.  Could do with a #define, I spose...
 			LoadString(hInst, 1000, dllVersionBuffer, sizeof(dllVersionBuffer));
-			//initall();
+
+			// and capture our activation context for use when loading extensions.
+			_LoadActCtxPointers();
+			if (pfnGetCurrentActCtx && pfnAddRefActCtx)
+				if ((*pfnGetCurrentActCtx)(&PyWin_DLLhActivationContext))
+					if (!(*pfnAddRefActCtx)(PyWin_DLLhActivationContext))
+						OutputDebugString("Python failed to load the default activation context\n");
 			break;
+
 		case DLL_PROCESS_DETACH:
+			if (pfnReleaseActCtx)
+				(*pfnReleaseActCtx)(PyWin_DLLhActivationContext);
 			break;
 	}
 	return TRUE;

Python/dynload_win.c

@@ -11,6 +11,10 @@
 #include "importdl.h"
 #include <windows.h>
 
+// "activation context" magic - see dl_nt.c...
+extern ULONG_PTR _Py_ActivateActCtx();
+void _Py_DeactivateActCtx(ULONG_PTR cookie);
+
 const struct filedescr _PyImport_DynLoadFiletab[] = {
 #ifdef _DEBUG
 	{"_d.pyd", "rb", C_EXTENSION},
@@ -172,6 +176,7 @@ dl_funcptr _PyImport_GetDynLoadFunc(const char *fqname, const char *shortname,
 		char pathbuf[260];
 		LPTSTR dummy;
 		unsigned int old_mode;
+		ULONG_PTR cookie = 0;
 		/* We use LoadLibraryEx so Windows looks for dependent DLLs 
 		    in directory of pathname first.  However, Windows95
 		    can sometimes not work correctly unless the absolute
@@ -184,10 +189,13 @@ dl_funcptr _PyImport_GetDynLoadFunc(const char *fqname, const char *shortname,
 		if (GetFullPathName(pathname,
 				    sizeof(pathbuf),
 				    pathbuf,
-				    &dummy))
+				    &dummy)) {
+			ULONG_PTR cookie = _Py_ActivateActCtx();
 			/* XXX This call doesn't exist in Windows CE */
 			hDLL = LoadLibraryEx(pathname, NULL,
 					     LOAD_WITH_ALTERED_SEARCH_PATH);
+			_Py_DeactivateActCtx(cookie);
+		}
 
 		/* restore old error mode settings */
 		SetErrorMode(old_mode);