问题
I've a DLL that embeds Python interpreter using the C/Python API. The DLL works fine if called one time, but if the DLL is called twice, the code cracks and my program catch memory error. The C code calling DLL is simple and the call to DLL function(Which calls Python interpreter) is done one time, if the second call(In the code) is not commented the code cracks and this happens only if "Numpy" is called in the Python code.
#include <stdio.h>
#include <conio.h>
#include <math.h>
#include <dll_simples.h>
int main() {
double in[] = { 4,2,5,4,2 };
double out[5] = {};
double a = 0;
double b = 0;
simuser(a,b,in,out);
//simuser(a, b, in, out); IF NOT COMMENTED -> ERROR
return 0;
}
I've commented Py_Finalize() in the DLL as suggested here and this post here affirms that from Py_Finalize() docs"Some extensions may not work properly if their initialization routine is called more than once; this can happen if an application calls Py_Initialize() and Py_Finalize() more than once." So i'd like to know why this happens and if any other thing could be done except calls "Py_Finalize()" only one time in the last call to DLL.
回答1:
Listing [Python 3.Docs]: ctypes - A foreign function library for Python.
dll00.h:
#pragma once
#if defined(_WIN32)
# if defined DLL0_EXPORTS
# define DLL00_EXPORT_API __declspec(dllexport)
# else
# define DLL00_EXPORT_API __declspec(dllimport)
# endif
#else
# define DLL00_EXPORT_API
#endif
#if defined(__cplusplus)
extern "C" {
#endif
DLL00_EXPORT_API int dll00Func00(double t, double delta, unsigned int size, const double *pIn, double *pOut);
#if defined(__cplusplus)
}
#endif
dll00.c:
#include <stdio.h>
#include "Python.h"
#define DLL0_EXPORTS
#include "dll00.h"
#define C_TAG "From C .dll"
int dll00Func00(double t, double delta, unsigned int size, const double *pIn, double *pOut) {
int res = 0;
printf("%s: in function\n", C_TAG);
const int isInit = Py_IsInitialized();
// Modify array calling Python functions
if (!isInit) {
printf("%s: initializing Python interpreter\n", C_TAG);
Py_Initialize();
}
res = PyRun_SimpleString("print(\"From Python (within C .dll): test\")");
for (unsigned int i = 0; i < size; i++) {
pOut[i] = pIn[i] * t + delta;
}
if (!isInit) {
printf("%s: uninitializing Python interpreter\n", C_TAG);
Py_Finalize();
}
return 0;
}
main00.c:
#include <stdio.h>
#include "dll00.h"
#define SIZE 4
int main() {
int res = 0;
double in[SIZE] = { 10.0, 11.0, 12.0, 13.0 };
double out[SIZE] = { 0 };
res = dll00Func00(2, 0.5, SIZE, in, out);
printf("Output array:\n");
for (unsigned int i = 0; i < SIZE; i++) {
printf("%.03f ", out[i]);
}
printf("\n");
return 0;
}
code00.py:
#!/usr/bin/env python
import sys
import ctypes as ct
DLL_NAME = "./dll00.dll"
def main(*argv):
DblPtr = ct.POINTER(ct.c_double)
size = 5
DblArr = ct.c_double * size
dll00 = ct.PyDLL(DLL_NAME)
dll00Func00 = dll00.dll00Func00
dll00Func00.argtypes = (ct.c_double, ct.c_double, ct.c_uint, DblPtr, DblPtr)
dll00Func00.restype = ct.c_int
in_arr = DblArr(*range(size))
out_arr = DblArr()
print("Output array:")
for i in range(size):
print("{:.3f}".format(out_arr[i]), end=" ")
print("\n")
res = dll00Func00(2, 2.5, size, in_arr, out_arr)
print("Output array:")
for i in range(size):
print("{:.3f}".format(out_arr[i]), end=" ")
print()
if __name__ == "__main__":
print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 if sys.maxsize > 0x100000000 else 32, sys.platform))
main(*sys.argv[1:])
print("\nDone.")
Notes:
- In Python, use ctypes.PyDLL as you're (indirectly) calling Python API functions
- In the .dll, use [Python 3.Docs]: Initialization, Finalization, and Threads - int Py_IsInitialized()
- As a side note, the if test is not needed in Py_Initialize's case as Py_Initialize simply returns if the interpreter is already initialized (so I left it there just for consistency), but it is needed for Py_Finalize as one wouldn't want to uninitialize the interpreter while still in Python.
So Py_Initialize / Py_Finalize pair doesn't work on "reference count" (every Py_Initialize call requires an Py_Finalize one)
- As a side note, the if test is not needed in Py_Initialize's case as Py_Initialize simply returns if the interpreter is already initialized (so I left it there just for consistency), but it is needed for Py_Finalize as one wouldn't want to uninitialize the interpreter while still in Python.
Calling Py_Initialize / Py_Finalize in the function, seems like an overkill (if the function is being called multiple times). I'd do 2 wrapper functions in the .dll and call:
- one at the beginning
- the other at the end
of the (C) program
Output:
e:\Work\Dev\StackOverflow\q059937552>sopr.bat *** Set shorter prompt to better fit when pasted in StackOverflow (or other) pages *** [prompt]> "c:\Install\pc032\Microsoft\VisualStudioCommunity\2017\VC\Auxiliary\Build\vcvarsall.bat" x64 ********************************************************************** ** Visual Studio 2017 Developer Command Prompt v15.9.19 ** Copyright (c) 2017 Microsoft Corporation ********************************************************************** [vcvarsall.bat] Environment initialized for: 'x64' [prompt]> dir /b code00.py dll00.c dll00.h main00.c [prompt]> cl /nologo /MD /DDLL /I"c:\Install\pc064\Python\Python\03.07.06\include" dll00.c /link /NOLOGO /DLL /OUT:dll00.dll /LIBPATH:"c:\Install\pc064\Python\Python\03.07.06\libs" dll00.c Creating library dll00.lib and object dll00.exp [prompt]> cl /nologo /MD /W0 main00.c /link /NOLOGO /OUT:main00_064.exe dll00.lib main00.c [prompt]> dir /b code00.py dll00.c dll00.dll dll00.exp dll00.h dll00.lib dll00.obj main00.c main00.obj main00_064.exe [prompt]> "e:\Work\Dev\VEnvs\py_pc064_03.07.06_test0\Scripts\python.exe" code00.py Python 3.7.6 (tags/v3.7.6:43364a7ae0, Dec 19 2019, 00:42:30) [MSC v.1916 64 bit (AMD64)] 64bit on win32 Output array: 0.000 0.000 0.000 0.000 0.000 From C .dll: in function From Python (within C .dll): test Output array: 2.500 4.500 6.500 8.500 10.500 Done. [prompt]> set PATH=%PATH%;c:\Install\pc064\Python\Python\03.07.06 [prompt]> main00_064.exe From C .dll: in function From C .dll: initializing Python interpreter From Python (within C .dll): test From C .dll: uninitializing Python interpreter Output array: 20.500 22.500 24.500 26.500
来源：https://stackoverflow.com/questions/59937552/c-dll-crack-when-called-from-python