AttributeError: free when taking ownership or freeing cdata

Question

如果我想获得在 C 中 malloced 的指针的所有权，docs for the Python cffi package and 说使用 ffi.gc 和 lib.free 作为析构函数。但是，当我这样做时，我在 lib.free 的调用中得到 AttributeError: free。 lib.free定义在哪里？

from tempfile import TemporaryDirectory
from weakref import WeakKeyDictionary

from cffi import FFI

common_header = """
typedef struct {
  int32_t length;
  double* values;
} my_struct;
"""

# FFI
ffi = FFI()

ffi.cdef(common_header + """
int func(my_struct*);
""")
ffi.set_source('_temp', common_header + """
int func(my_struct *input) {
  double* values = malloc(sizeof(double) * 3);
  input->length = 3;
  input->values = values;
  return 0;
}
""")

with TemporaryDirectory() as temp_dir:
    lib_path = ffi.compile(tmpdir=temp_dir)

    lib = ffi.dlopen(lib_path)

    func = lib.func

# Using the library
my_struct = ffi.new('my_struct*')
func(my_struct)

# Taking ownership of the malloced member
global_weakkey = WeakKeyDictionary()
global_weakkey[my_struct] = ffi.gc(my_struct.values, lib.free)
# AttributeError: free

Answer 1

文档没有强调这一点，但您需要将 free 作为库的 cdef 的一部分公开，就像任何其他函数一样，以便在 [=19] 上访问它=] 边。将 void free(void *ptr); 放在对 ffi.cdef 的调用中， free 函数将在编译后通过 lib.free 可用：

from tempfile import TemporaryDirectory
from weakref import WeakKeyDictionary

from cffi import FFI

common_header = """
typedef struct {
  int32_t length;
  double* values;
} my_struct;
"""

# FFI
ffi = FFI()

ffi.cdef(common_header + """
int func(my_struct*);
void free(void *ptr); // <-- Key to lib.free working later
""")
ffi.set_source('_temp', common_header + """
int func(my_struct *input) {
  double* values = malloc(sizeof(double) * 3);
  input->length = 3;
  input->values = values;
  return 0;
}
""")

with TemporaryDirectory() as temp_dir:
    lib_path = ffi.compile(tmpdir=temp_dir)

    lib = ffi.dlopen(lib_path)

    func = lib.func

# Using the library
my_struct = ffi.new('my_struct*')
func(my_struct)

# Taking ownership of the malloced member
global_weakkey = WeakKeyDictionary()
global_weakkey[my_struct] = ffi.gc(my_struct.values, lib.free)

AttributeError: free when taking ownership or freeing cdata

AttributeError: free when taking ownership or freeing cdata

python

python-cffi