c++ - 如何在类里面正确使用 boost channel (和光纤)？

Question

我正在尝试在类里面使用 boost channel 和光纤。这是一个简单的测试用例，工作正常，但它并不是我想要的。如果我将“line:1”移至“loc:1”，程序将挂起(gdb 在 c->push(a) 之后显示在 boost::fibers 内的自旋锁处).谁能指出我做错了什么来帮助我？谢谢。

这是运行并生成以下内容的示例代码，

#include <iostream>
#include <boost/fiber/all.hpp>

using namespace std;

template <class T>
class Block
{
    private:
        typedef boost::fibers::buffered_channel<T> channel_t;
        typedef boost::fibers::fiber fiber_t;
        fiber_t _thread_send;
        fiber_t _thread_recv;
        size_t _n;
        channel_t* _chan;

    public:
        Block(size_t n) : _n(n), _chan(nullptr) {
            // >>>>>>>>>> loc:1 <<<<<<<<<<<
        }
        virtual ~Block() {}
        void _send(channel_t *c) {
            cout << __func__ << endl;
            int a = 1000;
            cout << "Sending: " << a << endl;
            c->push(a);
        }
        void _recv(channel_t *c) {
            cout << __func__ << endl;
            int a = 0;
            c->pop(a);
            cout << "Received: " << a << endl;
        }
        void do_work() {
            cout << "do_work\n";
            channel_t temp{_n}; _chan = &temp; // <<<<<<<<<<<< line:1
            _thread_send = boost::fibers::fiber(bind(&Block::_send, this, _chan));
            _thread_recv = boost::fibers::fiber(bind(&Block::_recv, this, _chan));
            _thread_send.join();
            _thread_recv.join();
        }
};

int main()
{
    Block<int> B(2);
    B.do_work(); 
    return 0;
}

输出:

do_work
_send
Sending: 1000
_recv
Received: 1000

编译使用:

GNU/Linux 64 bit x86-64
g++ (GCC) 7.1.1 2017051
boost 1.64.0
g++ -c --std=c++14 -g -Wall -Wpedantic boost_channels.cpp -o boost_channels.o
g++ -lboost_context -lboost_fiber boost_channels.o -o boost_channels

Answer 1

channel_t temp{_n}; _chan = &temp; // <<<<<<<<<<<< line:1

in Block() 将不起作用，因为 temp 在离开 Block() 后超出范围' s body 和 _chan 将指向垃圾/释放的内存

两个版本是可能的:

1) 保持 channel temp 为 do_work() 的局部变量:

template <class T>
class Block
{
private:
    typedef boost::fibers::buffered_channel<T> channel_t;
    typedef boost::fibers::fiber fiber_t;
    fiber_t _thread_send;
    fiber_t _thread_recv;
    size_t _n;

public:
    Block(size_t n) : _n(n) {
    }
    virtual ~Block() {}
    void _send(channel_t *c) {
        cout << __func__ << endl;
        int a = 1000;
        cout << "Sending: " << a << endl;
        c->push(a);
    }
    void _recv(channel_t *c) {
        cout << __func__ << endl;
        int a = 0;
        c->pop(a);
        cout << "Received: " << a << endl;
    }
    void do_work() {
        cout << "do_work\n";
        channel_t chan{_n};
        _thread_send = boost::fibers::fiber(bind(&Block::_send, this, & chan));
        _thread_recv = boost::fibers::fiber(bind(&Block::_recv, this, & chan));
        _thread_send.join();
        _thread_recv.join();
    }
};

2) 保持 channel temp 为 Block<> 的成员变量:

template <class T>
class Block
{
private:
    typedef boost::fibers::buffered_channel<T> channel_t;
    typedef boost::fibers::fiber fiber_t;
    fiber_t _thread_send;
    fiber_t _thread_recv;
    channel_t _chan;

public:
    Block(size_t n) : _chan(n) {
    }
    virtual ~Block() {}
    void _send(channel_t *c) {
        cout << __func__ << endl;
        int a = 1000;
        cout << "Sending: " << a << endl;
        c->push(a);
    }
    void _recv(channel_t *c) {
        cout << __func__ << endl;
        int a = 0;
        c->pop(a);
        cout << "Received: " << a << endl;
    }
    void do_work() {
        cout << "do_work\n";
        _thread_send = boost::fibers::fiber(bind(&Block::_send, this, & _chan));
        _thread_recv = boost::fibers::fiber(bind(&Block::_recv, this, & _chan));
        _thread_send.join();
        _thread_recv.join();
    }
};

两个版本都生成:

do_work
_send
Sending: 1000
_recv
Received: 1000