我设计了一个 C++ 系统,它从在单独线程中运行的过程调用用户定义的回调。简化版system.hpp
看起来像这样:
#pragma once
#include <atomic>
#include <chrono>
#include <functional>
#include <thread>
class System
{
public:
using Callback = std::function<void(int)>;
System(): t_(), cb_(), stop_(true) {}
~System()
{
stop();
}
bool start()
{
if (t_.joinable()) return false;
stop_ = false;
t_ = std::thread([this]()
{
while (!stop_)
{
std::this_thread::sleep_for(std::chrono::milliseconds(100));
if (cb_) cb_(1234);
}
});
return true;
}
bool stop()
{
if (!t_.joinable()) return false;
stop_ = true;
t_.join();
return true;
}
bool registerCallback(Callback cb)
{
if (t_.joinable()) return false;
cb_ = cb;
return true;
}
private:
std::thread t_;
Callback cb_;
std::atomic_bool stop_;
};
它工作得很好,可以用这个简短的例子进行测试main.cpp
:
#include <iostream>
#include "system.hpp"
int g_counter = 0;
void foo(int i)
{
std::cout << i << std::endl;
g_counter++;
}
int main()
{
System s;
s.registerCallback(foo);
s.start();
while (g_counter < 3)
{
std::this_thread::sleep_for(std::chrono::milliseconds(1));
}
s.stop();
return 0;
}
这将输出1234
几次然后就会停止。然而,我在尝试为我的创建 python 绑定时遇到了问题System
。如果我将 python 函数注册为回调,我的程序将在调用后死锁System::stop
。我对这个话题进行了一些调查,看来我面临着这个问题GIL。可重现的例子:
binding.cpp
:
#include "pybind11/functional.h"
#include "pybind11/pybind11.h"
#include "system.hpp"
namespace py = pybind11;
PYBIND11_MODULE(mysystembinding, m) {
py::class_<System>(m, "System")
.def(py::init<>())
.def("start", &System::start)
.def("stop", &System::stop)
.def("registerCallback", &System::registerCallback);
}
蟒蛇脚本:
#!/usr/bin/env python
import mysystembinding
import time
g_counter = 0
def foo(i):
global g_counter
print(i)
g_counter = g_counter + 1
s = mysystembinding.System()
s.registerCallback(foo)
s.start()
while g_counter < 3:
time.sleep(1)
s.stop()
我已阅读pybind11 文档关于在 C++ 端获取或释放 GIL 的可能性的部分。然而,我未能摆脱我的案例中出现的僵局:
PYBIND11_MODULE(mysystembinding, m) {
py::class_<System>(m, "System")
.def(py::init<>())
.def("start", &System::start)
.def("stop", &System::stop)
.def("registerCallback", [](System* s, System::Callback cb)
{
s->registerCallback([cb](int i)
{
// py::gil_scoped_acquire acquire;
// py::gil_scoped_release release;
cb(i);
});
});
}
如果我打电话py::gil_scoped_acquire acquire;
在调用回调之前,无论如何都会发生死锁。
如果我打电话py::gil_scoped_release release;
在调用回调之前,我得到
致命的 Python 错误:PyEval_SaveThread:NULL tstate
我应该怎么做才能将 python 函数注册为回调并避免死锁?