在Python中，如何使用ctypes将回调数组作为参数传递给C函数？

Question

这是我的问题，我有一个用C编写的遗留库（.so），API如下：

typedef void (*CALLBACK)( void);
typedef CALLBACK CALLBACK_TBL[ 5 ];
void init(CALLBACK_TBL callbackTbl)
{
        T_MYCALLBACK *myCallback1 = (T_MYCALLBACK *)(callbackTbl[0]);
        if (myCallback1 )
        {
            myCallback1(2,3);
        }
}

当然，因为它是一个遗留库，所以我不能更改API签名

现在从Python开始，我尝试使用Python中定义的回调调用init：

CallbackType1 = ctypes.CFUNCTYPE(None, c_ulong, c_ulong)
CallbackType2 = ctypes.CFUNCTYPE(None, c_ubyte, c_ubyte)
...
CallbackType5 = ctypes.CFUNCTYPE(None, c_int32, c_int32)


def callback1(long1, long2):
    print("callback1")

def callback2(bool1, bool2):
    print("callback2")
...
def callback5(int1, int2):
    print("callback5")

但我无法理解我应该如何进行这样一系列回调：

_callback1 = CallbackType1(callback1)
_callback2 = CallbackType1(callback2)
...
_callback5 = CallbackType1(callback5)

lib = CDLL("lib.so")
lib.init(....) ?????

有人有主意吗

Answer 1

清单[Python 3.Docs]: ctypes - A foreign function library for Python

最简单的方法是将C代码保持原样（不要过多考虑），并将其转换为Python：

>>> import ctypes as ct
>>>
>>> Callback = ct.CFUNCTYPE(None)  # Generic callback type - might be a ct.c_void_p as well
>>> CallbackArray = Callback * 5
>>>
>>> Callback1 = ct.CFUNCTYPE(None, ct.c_ulong, ct.c_ulong)
>>> def func1(long1, long2): pass
...
>>> callback1 = Callback1(func1)
>>>
>>> # The rest of Callback# func# and callback#
>>>
>>> callback_array = CallbackArray()
>>> callback_array
<__main__.CFunctionType_Array_5 object at 0x000001517253CA48>
>>> callback_array[0]
<CFunctionType object at 0x000001517240BBA8>
>>>
>>> callback_array[0] = ct.cast(callback1, Callback)  # !!! Conversion needed !!!
>>> callback_array[0]
<CFunctionType object at 0x000001517240BE18>

>>> # Same thing for callback_array[1] .. callback_array[4]

其余的代码（我没有将其粘贴到控制台中，因为它不起作用）：

lib = ct.CDLL("./lib.so")

lib.init.argtypes = [CallbackArray]  # Check the URL at the end

lib.init(callback_array)

始终为从.dll导入的函数定义argtypes（和restype）。查看[SO]: C function called from Python via ctypes returns incorrect value (@CristiFati's answer)了解更多详细信息

Answer 2

一个有效的例子就好了。我在下面创建了一个，但如果它不适合您，请使用与您的情况相匹配的类似DLL示例更新您的问题：

test.cpp

typedef void (*CALLBACK)(); // generic
typedef void (*CALLBACK1)(long,long);
typedef void (*CALLBACK2)(bool,bool);
typedef void (*CALLBACK3)(int,int,int);

typedef CALLBACK CALLBACK_TBL[3];

extern "C" __declspec(dllexport)
void init(CALLBACK_TBL callbackTbl)
{
    ((CALLBACK1)callbackTbl[0])(1L,2L);
    ((CALLBACK2)callbackTbl[1])(true,false);
    ((CALLBACK3)callbackTbl[2])(1,2,3);
}

test.py

from ctypes import *

CALLBACK1 = CFUNCTYPE(None,c_long,c_long)
CALLBACK2 = CFUNCTYPE(None,c_bool,c_bool)
CALLBACK3 = CFUNCTYPE(None,c_int,c_int,c_int)

class CALLBACK_TBL(Structure):
    _fields_ = [('cb1',CALLBACK1),
                ('cb2',CALLBACK2),
                ('cb3',CALLBACK3)]

@CALLBACK1
def callback1(a,b):
    print('callback1',a,b)

@CALLBACK2
def callback2(a,b):
    print('callback2',a,b)

@CALLBACK3
def callback3(a,b,c):
    print('callback3',a,b,c)

cbt = CALLBACK_TBL(callback1,callback2,callback3)

dll = CDLL('./test')
dll.init.argtypes = CALLBACK_TBL,
dll.init.restype = None

dll.init(cbt)

输出：

callback1 1 2
callback2 True False
callback3 1 2 3