Python CFFI+7z.dll（COM）==访问冲突（有时）

Question

我已经将我的代码缩短为一个最小的用例。在

脚本总是会完成，但大约50%的时间它会导致内存访问冲突/崩溃。在

这是在Windows7上使用64位的Python3

这段代码应该遍历7zip的所有处理程序，并说明它们支持哪些扩展（一个空格分隔的列表，可能是空的。。。不是空的，只是bstrVal=L“”）

#!/usr/bin/python
from cffi import FFI
ffi = FFI()
ffi.cdef("""

typedef struct PROPVARIANT {
    unsigned short    vt;
    unsigned short    wReserved1;
    unsigned short    wReserved2;
    unsigned short    wReserved3;
    union {
        int          intVal;
        wchar_t*      bstrVal;
        /* shortened for clarity */
    };
} PROPVARIANT;

typedef unsigned long long HRESULT;
typedef uint32_t PROPID;

HRESULT GetNumberOfFormats(uint32_t * numFormats);
HRESULT GetHandlerProperty2(uint32_t index, PROPID propID, PROPVARIANT * value);
""")

S_OK = 0x00000000  # Operation successful
VT_BSTR = 8
kExtension = 2

dll7z = ffi.dlopen('7z.dll')
num_formats = ffi.new('uint32_t*')
assert dll7z.GetNumberOfFormats(num_formats) == S_OK
print(num_formats[0])

tmp_pvar = ffi.new('PROPVARIANT*')
for i in range(num_formats[0]):
    assert dll7z.GetHandlerProperty2(i, kExtension, tmp_pvar) == S_OK
    assert tmp_pvar != ffi.NULL
    assert tmp_pvar[0].vt == VT_BSTR

    print(ffi.string(tmp_pvar[0].bstrVal))

令人恼火的是，等效的ctypes代码似乎可以正常工作。在

^{pr2}$

Answer 1

好的，这看起来像一个CFFI错误。在

如果我手动使用malloc/free/memset，它可以正常工作。在

代码：

from cffi import FFI
ffi = FFI()
ffi.cdef("""

typedef struct PROPVARIANT {
    unsigned short    vt;
    unsigned short    wReserved1;
    unsigned short    wReserved2;
    unsigned short    wReserved3;
    union {
        int          intVal;
        wchar_t*      bstrVal;
        /* shortened for clarity */
    };
} PROPVARIANT;

typedef unsigned long long HRESULT;
typedef uint32_t PROPID;

HRESULT GetNumberOfFormats(uint32_t * numFormats);
HRESULT GetHandlerProperty2(uint32_t index, PROPID propID, PROPVARIANT * value);

void * malloc(size_t);
void memset(void*, int, int);
void free(void*);
""")

S_OK = 0x00000000  # Operation successful
VT_BSTR = 8
kExtension = 2

dll7z = ffi.dlopen('7z.dll')
C = ffi.dlopen(None)

num_formats = ffi.new('uint32_t*')
assert dll7z.GetNumberOfFormats(num_formats) == S_OK
print(num_formats[0])

tmp_pvar = ffi.cast("PROPVARIANT*", C.malloc(ffi.sizeof('PROPVARIANT')))
C.memset(tmp_pvar, 0, ffi.sizeof('PROPVARIANT'))

for i in range(num_formats[0]):
    assert dll7z.GetHandlerProperty2(i, kExtension, tmp_pvar) == S_OK
    assert tmp_pvar != ffi.NULL
    assert tmp_pvar[0].vt == VT_BSTR

    print(ffi.string(tmp_pvar[0].bstrVal))

C.free(tmp_pvar)