[英]Segmentation fault when using ctypes and threading
I wrote a Python wrapper for a C library using ctypes
. 我使用
ctypes
为C库编写了Python包装器。 Everything worked fine, until I tried it with the threading
module. 一切工作正常,直到我使用
threading
模块对其进行了尝试。
Here is a small example to reproduce it: 这是一个重现它的小例子:
#include <stdlib.h>
#include <assert.h>
char *foo_init() {
char *result = (char*)malloc(sizeof(char));
assert(result);
return result;
}
char foo_get(const char* p) {
return *p;
}
void foo_set(char *p, char value) {
*p = value;
}
void foo_del(char *p) {
free(p);
}
import threading
import ctypes
libfoo=ctypes.CDLL('foo.so')
libfoo.foo_init.restype = ctypes.c_void_p
libfoo.foo_get.restype = ctypes.c_char
class Foo:
def __init__(self):
self.__obj__ = libfoo.foo_init()
def get(self):
return libfoo.foo_get(self.__obj__)
def set(self, value):
libfoo.foo_set(self.__obj__, ctypes.c_char(value))
def __del__(self):
libfoo.foo_del(self.__obj__)
x = Foo()
x.set(b'x')
print(x.get())
def compute():
y = Foo()
y.set(b'y')
print(y.get())
t = threading.Thread(target=compute)
t.start()
t.join()
Compilation: 汇编:
gcc -Wall -shared -o foo.so -fPIC foo.c
Execution: 执行:
export LD_LIBRARY_PATH=.
python3 foo.py
Result: 结果:
b'x'
[1] 8627 segmentation fault python3 foo.py
We see here that x.get()
is correctly printed whereas y.get()
does a segmentation fault. 我们在这里看到
x.get()
正确打印,而y.get()
则出现分段错误。 Thus, it seems that there is a problem linked to ctypes
and threading
. 因此,似乎存在与
ctypes
和threading
相关的问题。
Note that if I move the initialization of y
outside of the compute
function, then the program exits normally. 请注意,如果将
y
的初始化移至compute
函数之外,则程序将正常退出。
Moreover, each of the functions which manipulate the pointer produce a segmentation fault (eg if I just keep the __init__
and __del__
functions, there is still a crash). 而且,操纵指针的每个函数都会产生分段错误(例如,如果我只保留
__init__
和__del__
函数,则仍然会发生崩溃)。
Any idea on how to fix this? 关于如何解决此问题的任何想法?
@user2357112 gave me the answer in comments: adding the (good) return type and the arguments types is important. @ user2357112在注释中给了我答案:添加(good)返回类型和参数类型很重要。
Replacing the beginning of foo.py
by the following fix the problem: 通过以下替换
foo.py
的开头foo.py
此问题:
libfoo.foo_init.restype = ctypes.POINTER(ctypes.c_char)
libfoo.foo_init.argtypes = []
libfoo.foo_get.restype = ctypes.c_char
libfoo.foo_get.argtypes = [ctypes.POINTER(ctypes.c_char)]
libfoo.foo_set.argtypes = [ctypes.POINTER(ctypes.c_char), ctypes.c_char]
libfoo.foo_del.argtypes = [ctypes.POINTER(ctypes.c_char)]
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