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属性错误:获取所有权或释放CDATA时是免费的

python-cffi python

drhagen · 技术社区 · 5 年前

如果我想拥有一个指针 malloc Ed在C中, docs for the Python cffi package 和 this answer 说要用 ffi.gc 具有 lib.free 作为析构函数。但是,当我这样做的时候,我 AttributeError: free 随时待命 自由库 . 在哪里 自由库 定义?

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

1 回复 | 直到 5 年前

drhagen 5 年前

医生不强调这一点,但你需要暴露 free 作为自由党的一部分 cdef 就像在Python端访问它的任何其他函数一样。放 void free(void *ptr); 在呼叫中 ffi.cdef 以及 自由的 功能将通过 lib.free 编译后:

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)

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