Pybind11 多处理挂起

Question

我正在编写一个使用 Pybind11 嵌入 Python 解释器（Windows，64 位，Visual C++ 2017）的应用程序。从 Python 开始，我需要生成多个进程，但它似乎不起作用。我尝试使用以下代码作为测试：

import multiprocessing
import os
import sys
import time
print("This is the name of the script: ", sys.argv[0])
print("Number of arguments: ", len(sys.argv))
print("The arguments are: " , str(sys.argv))
prefix=str(os.getpid())+"-"
if len(sys.argv) > 1:
    __name__ = "__mp_main__"

def print_cube(num):
    """
    function to print cube of given num
    """
    print("Cube: {}".format(num * num * num))

def print_square(num):
    """
    function to print square of given num
    """
    print("Square: {}".format(num * num))

print(__name__)

if __name__ == "__main__":
    print(prefix, "checkpoint 1")
    # creating processes
    p1 = multiprocessing.Process(target=print_square, args=(10, ))
    p1.daemon = True
    p2 = multiprocessing.Process(target=print_cube, args=(10, ))

    # starting process 1
    p1.start()
    print(prefix, "checkpoint 2")

    # starting process 2
    p2.start()
    print(prefix, "checkpoint 3")

    # wait until process 1 is finished
    print(prefix, "checkpoint 4")
    p1.join()
    print(prefix, "checkpoint 5")
    # wait until process 2 is finished
    p2.join()
    print(prefix, "checkpoint 6")

    # both processes finished
    print("Done!")
print(prefix, "checkpoint 7")
time.sleep(10)

运行它在命令提示符下使用 Python，我得到：

This is the name of the script:  mp.py
Number of arguments:  1
The arguments are:  ['mp.py']
__main__
12872- checkpoint 1
12872- checkpoint 2
This is the name of the script:  C:\tmp\mp.py
Number of arguments:  1
The arguments are:  ['C:\tmp\mp.py']
__mp_main__
7744- checkpoint 7
Square: 100
12872- checkpoint 3
12872- checkpoint 4
12872- checkpoint 5
This is the name of the script:  C:\tmp\mp.py
Number of arguments:  1
The arguments are:  ['C:\tmp\mp.py']
__mp_main__
15020- checkpoint 7
Cube: 1000
12872- checkpoint 6
Done!
12872- checkpoint 7

这是正确的。如果我使用 Pybind11 从 C++ 项目中尝试相同的操作，输出为：

This is the name of the script:  C:\AGPX\Documenti\TestPyBind\x64\Debug\TestPyBind.exe
Number of arguments:  1
The arguments are:  ['C:\AGPX\Documenti\TestPyBind\x64\Debug\TestPyBind.exe']
__main__
4440- checkpoint 1
This is the name of the script:  C:\AGPX\Documenti\TestPyBind\x64\Debug\TestPyBind.exe
Number of arguments:  4
The arguments are:  ['C:\AGPX\Documenti\TestPyBind\x64\Debug\TestPyBind.exe', '-c', 'from multiprocessing.spawn import spawn_main; spawn_main(parent_pid=4440, pipe_handle=128)', '--multiprocessing-fork']
__mp_main__
10176- checkpoint 7

请注意，在这种情况下，变量 __name__ 始终设置为“__main__”，因此我必须手动将其更改（对于生成的进程）为“[=16=” ]'（由于 sys.argv，我可以检测到子进程）。这是第一个奇怪的行为。父进程的 pid 为 4440，我可以在进程资源管理器中看到该进程。第一个子进程的 pid 为 10176，它到达末尾 'checkpoint 7' 并且进程从进程资源管理器中消失。但是，主进程不打印 'checkpoint 2'，看起来它挂在 'p1.start()' 上，我不明白为什么。完整的C++代码为：

#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <pybind11/stl_bind.h>
#include <pybind11/embed.h>
#include <iostream>

namespace py = pybind11;
using namespace py::literals;

int wmain(int argc, wchar_t **argv)
{
    py::initialize_interpreter();
    PySys_SetArgv(argc, argv);

    std::string pyCode = std::string(R"(
import multiprocessing
import os
import sys
import time
print("This is the name of the script: ", sys.argv[0])
print("Number of arguments: ", len(sys.argv))
print("The arguments are: " , str(sys.argv))
prefix=str(os.getpid())+"-"
if len(sys.argv) > 1:
    __name__ = "__mp_main__"

def print_cube(num):
    """
    function to print cube of given num
    """
    print("Cube: {}".format(num * num * num))

def print_square(num):
    """
    function to print square of given num
    """
    print("Square: {}".format(num * num))

print(__name__)

if __name__ == "__main__":
    print(prefix, "checkpoint 1")
    # creating processes
    p1 = multiprocessing.Process(target=print_square, args=(10, ))
    p1.daemon = True
    p2 = multiprocessing.Process(target=print_cube, args=(10, ))

    # starting process 1
    p1.start()
    print(prefix, "checkpoint 2")

    # starting process 2
    p2.start()
    print(prefix, "checkpoint 3")

    # wait until process 1 is finished
    print(prefix, "checkpoint 4")
    p1.join()
    print(prefix, "checkpoint 5")
    # wait until process 2 is finished
    p2.join()
    print(prefix, "checkpoint 6")

    # both processes finished
    print("Done!")
print(prefix, "checkpoint 7")
time.sleep(10)
)");
    try
    {
        py::exec(pyCode);
    } catch (const std::exception &e) {
        std::cout << e.what();
    }
    py::finalize_interpreter();
}

谁能向我解释一下如何解决这个问题？

提前致谢（我为我的英语道歉）。

Answer 1

好的，感谢这个 link: https://blender.stackexchange.com/questions/8530/how-to-get-python-multiprocessing-module-working-on-windows，我解决了这个奇怪的问题（似乎与 Windows 相关）。这不是 Pybind11 问题，而是 Python C API 本身。您可以通过将 sys.executable 设置为 python 解释器可执行文件 (python.exe) 的路径并将 python 代码写入文件并将路径设置为__file__ 变量。也就是我要加上：

import sys
sys.executable = "C:\Users\MyUserName\Miniconda3\python.exe"
__file__ = "C:\tmp\run.py"

并且我需要将python代码写入__file__指定的文件，即：

FILE *f = nullptr;
fopen_s(&f, "c:\tmp\run.py", "wt");
fprintf(f, "%s", pyCode.c_str());
fclose(f);

就在执行之前 py::exec(pyCode).

另外代码：

if len(sys.argv) > 1:
    __name__ = "__mp_main__"

不再需要。但是，请注意，以这种方式运行的进程不再嵌入，不幸的是，如果你想直接将 C++ 模块传递给它们，你不能这样做。

希望这可以帮助到其他人。

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