Question

我正在尝试将Python回调注册到我的C库。当使用PyCallable_Check()检查回调是否为有效的Python回调时，它会出现段错误...

这是重复此问题的简单代码：

#include <Python.h>
#include <stdio.h>

typedef void (*event_handler_t)(const void* uuid, const uint8_t* data, size_t data_length, void* user_data);

PyObject * m_handler;
void *m_user_data;

void register_notification(void* connection, PyObject * event_handler, void* user_data) {
    if (!PyCallable_Check(event_handler)) {
        printf("parameter must be callable\n");
        return;
    }

    m_handler = event_handler;
    m_user_data = user_data;
}

要构建它：

gcc -fPIC -shared `pkg-config --cflags python-3.6` my_module.c `pkg-config --libs python-3.6` -o minimal_check.so`

这是触发问题的python脚本：

from ctypes import *

mymodule = CDLL("minimal_check.so")

event_handler_type = CFUNCTYPE(None, c_void_p, c_void_p, c_size_t, c_void_p)

register_notification = mymodule.register_notification
register_notification.argtypes = [c_void_p, event_handler_type, c_void_p]

def my_callback(uuid_ptr, data, data_len, user_data):
    pass

register_notification(None, event_handler_type(my_callback), None)

看着coredump，崩溃似乎肯定在PyCallable_Check中：

#0  0x0000000000531a0d in PyCallable_Check () at ../Objects/object.c:1307
#1  0x00007febcd24e72a in register_notification () from /tmp/minimal_check/minimal_check.so
#2  0x00007febcd455dae in ffi_call_unix64 () from /usr/lib/x86_64-linux-gnu/libffi.so.6
#3  0x00007febcd45571f in ffi_call () from /usr/lib/x86_64-linux-gnu/libffi.so.6
#4  0x00007febcd6a1c64 in _call_function_pointer (argcount=3, resmem=0x7ffe670393c0, restype=<optimized out>, atypes=0x7ffe67039380, avalues=0x7ffe670393a0, pProc=0x7febcd24e70a <register_notification>, 
    flags=4353) at ./Modules/_ctypes/callproc.c:831
#5  _ctypes_callproc () at ./Modules/_ctypes/callproc.c:1195
#6  0x00007febcd6a2404 in PyCFuncPtr_call () at ./Modules/_ctypes/_ctypes.c:3970
#7  0x000000000057ec0c in _PyObject_FastCallDict (kwargs=<optimized out>, nargs=<optimized out>, args=<optimized out>, func=<_FuncPtr(__name__='register_notification') at remote 0x7febcf541750>)
    at ../Objects/tupleobject.c:131
#8  _PyObject_FastCallKeywords () at ../Objects/abstract.c:2496
#9  0x00000000004f88ba in call_function () at ../Python/ceval.c:4875
#10 0x00000000004f98c7 in _PyEval_EvalFrameDefault () at ../Python/ceval.c:3335
#11 0x00000000004f6128 in PyEval_EvalFrameEx (throwflag=0, f=Frame 0x140ebb8, for file minimal_check.py, line 15, in <module> ()) at ../Python/ceval.c:4166
#12 _PyEval_EvalCodeWithName.lto_priv.1581 () at ../Python/ceval.c:4166
#13 0x00000000004f9023 in PyEval_EvalCodeEx (closure=0x0, kwdefs=0x0, defcount=0, defs=0x0, kwcount=0, kws=0x0, argcount=0, args=0x0, locals=<optimized out>, globals=<optimized out>, _co=<optimized out>)
    at ../Python/ceval.c:4187
#14 PyEval_EvalCode (co=<optimized out>, globals=<optimized out>, locals=<optimized out>) at ../Python/ceval.c:731
#15 0x00000000006415b2 in run_mod () at ../Python/pythonrun.c:1025
#16 0x000000000064166a in PyRun_FileExFlags () at ../Python/pythonrun.c:978
#17 0x0000000000643730 in PyRun_SimpleFileExFlags () at ../Python/pythonrun.c:419
#18 0x000000000062b26e in run_file (p_cf=0x7ffe670399ec, filename=<optimized out>, fp=<optimized out>) at ../Modules/main.c:340
#19 Py_Main () at ../Modules/main.c:810
#20 0x00000000004b4cb0 in main (argc=2, argv=0x7ffe67039be8) at ../Programs/python.c:69

Answer 1

基于@AnttiHaapala的评论，我设法使某些方法起作用。所以我：

删除了CFUNCTYPE，因为它是传递给的Python对象回调
直接将python回调传递给register_notification（）
将回调类型更改为py_object

似乎可行。为了演示起见，以防万一它可以帮助将来遇到同样问题的其他人，我添加了代码来演示回调。

这是新代码：

#include <Python.h>
#include <stdio.h>

typedef void (*event_handler_t)(void* user_data);

PyObject *m_handler;
PyObject *m_user_data;

void register_notification(void* connection, PyObject *event_handler, PyObject *user_data) {
    if (!PyCallable_Check(event_handler)) {
        printf("parameter must be callable\n");
        return;
    }

    m_handler = event_handler;
    m_user_data = user_data;

    PyGILState_STATE d_gstate;
    d_gstate = PyGILState_Ensure();

    PyObject *arglist = Py_BuildValue("(O)", user_data);
    PyObject *result = PyEval_CallObject(event_handler, arglist);

    PyGILState_Release(d_gstate);

    if (result != NULL) {
        Py_DECREF(result);
    }
}

还有python代码：

from ctypes import *

mymodule = CDLL("minimal_check.so")

register_notification = mymodule.register_notification
register_notification.argtypes = [c_void_p, py_object, py_object]

def my_callback(user_data):
    print("From callback: %s" % user_data)

register_notification(c_void_p(None), my_callback, "Hello World")

Python C扩展：检查Python回调是否有效时出现Segfault

1 个答案: