ctypes - unloading implicitly loaded dlls
scottpig1 at comcast.net
Mon Jul 28 02:54:26 CEST 2008
(my apologies if this is a repost, but it sure seems like the first
attempt disappeared into the ether...)
I'm writing a program that uses functionality from two different sets of
cdlls which reside in two different directories, call them 'libA.dll'
and 'libB.dll'. Although I don't directly use it, both directories
contain a dll with the same name, although they aren't in fact
identical. Call them, "libC.dll". However, the c-functions I call from
the clls I do use seem to implicitly use "libC.dll". The problem that
occurs after I load one dll and call functions in it, when I try to load
the second dll I get windows errors because the second dll tries to call
a function in its version of libC.dll, but it finds the version meant
for libB.dll, which doesn't contain that function.
Oy, I hope some sample code makes it clearer:
A = ctypes.cdll.LoadLibrary('/path1/libA.dll')
A.foo() # implicitly uses '/path1/libC.dll'
B = ctypes.cdll.LoadLibrary('/path2/libB.dll')
# "The procedure entry point some_func could not be located
# in the dynamic link library libC.dll.":
# libB.dll wants to use code from '/path2/libC.dll', but
# instead it finds '/path1/libC.dll' already loaded
# in memory, which doesn't
# contain the function call it wants.
Assuming my understanding of things is correct, then I believe what I
need to do is to remove /path1/libC.dll from memory before I try loading
libB.dll, but I haven't found any way of doing that. Can anyone offer
my some suggestions? Or, am I S.O.L.?
* the two sets of dlls are supplied by a vendor for working with its
COTS packages; I don't have any control over the dll names used or the
* If I leave out the call to A.foo(), then I don't crash, but if I leave
out the FreeLibrary call as well then I do crash.
* I've tried manipulating the PATH before loading the dlls, to no effect.
* I've tried del'ing A and running gc.collect() before loading B.
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