从Python调用C DLL时出现裂纹

Question

我有一个DLL，它使用C/Python API嵌入Python解释器。如果调用一次DLL，它可以正常工作，但是如果调用两次DLL，代码就会崩溃，我的程序会捕获内存错误。 调用DLL的C代码很简单，对DLL函数的调用（调用Python解释器）只执行一次，如果第二次调用（在代码中）未被注释，则代码会破裂，并且只有在Python代码中调用“Numpy”时才会发生这种情况

#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;
 }

我已经按照建议here在DLL中注释了Py_Finalize（），这篇文章here确认了Py_Finalize（）文档中的“如果多次调用其初始化例程，则某些扩展可能无法正常工作；如果应用程序多次调用Py_Initialize（）和Py_Finalize（），则可能会发生这种情况。”所以我想知道为什么会发生这种情况，以及除了在最后一次调用DLL时只调用一次“Py_Finalize（）”之外，是否还有其他事情可以做

Answer 1

清单[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.")

注释：

• 在Python中，当（间接地调用pythonapi函数时，使用ctypes.PyDLL
• 在.dll中，使用[Python 3.Docs]: Initialization, Finalization, and Threads - intPy_IsInitialized()
  • 作为旁注，Py_Initialize的情况下不需要if测试，因为Py_Initialize只是在解释器已经初始化的情况下返回（因此我把它放在那里只是为了一致性），但是Py_Finalize需要它，因为人们不想在Python中取消解释器的初始化
    因此Py\u Initialize/Py\u Finalize对不适用于“引用计数”（每个Py\u Initialize调用都需要一个Py\u Finalize对）

• 在函数中调用Py\u Initialize/Py\u Finalize，似乎有点过分（如果函数被多次调用）。我将在.dll中执行两个包装函数并调用：

  • 一开始
  • 另一个在最后

  （C）计划的

输出：

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