代码之家 › 专栏 › 技术社区 › zxctatar

如何在一个类中运行两个异步定时器

asio boost-asio boost c++

zxctatar · 技术社区 · 1 年前

我想让第二个计时器在第二个开始工作半秒后开始工作,但当第二个定时器开始工作时,终端显示的内容与我想要的完全不同。如果它在执行第二个定时器之前没有施加限制,那么它们都可以正常工作

#include <iostream>
#include <functional>
#include <boost/asio.hpp>

class print{
public:
    print(boost::asio::io_context& io) : timer_(io, boost::asio::chrono::seconds(1)), count_(0){
        timer_.async_wait(std::bind(&print::printer, this));
    }

    void printer(){
        if(count_ < 5){
            std::cout << count_ << "\n";
            ++count_;

            timer_.expires_at(timer_.expiry() + boost::asio::chrono::seconds(1));
            timer_.async_wait(std::bind(&print::printer, this));
        }
    }

    ~print(){
        std::cout << "Last num " << count_ << "\n";
    }
private:
    boost::asio::steady_timer timer_;
    int count_;
};

int main(){
    boost::asio::io_context io;
    
    print p(io);

    boost::asio::steady_timer t(io, boost::asio::chrono::seconds(2));
    t.async_wait([&io](const boost::system::error_code& ec){
        if(!ec){
            print pp(io);
        }
    });

    io.run();   
}

这就是终端输出的

0,
1,
Last num 0,
2,
3,
4,
Last num 5.

1 回复 | 直到 1 年前

sehe 1 年前

第二个定时器 pp 是一个局部变量。它会立即被销毁。

因此,异步操作使用一个已删除的实例并调用 Undefined Behaviour .

您可能应该通过实际接收来检测取消 error_code 在完成处理程序中。这个 std::bind 表情默默地为你放下,现在。

你可以使用某种动态分配。我还强烈建议将间隔计时器的概念和执行的操作分开并推广:

struct Timer {
    using Callback = std::function<bool()>;

    Timer(asio::any_io_executor ex, duration d, Callback cb)
        : timer_(ex, d)
        , interval_(d)
        , cb_(std::move(cb)) { do_loop(); }

  private:
    asio::steady_timer timer_;
    duration           interval_;
    Callback           cb_;

    void do_loop() {
        timer_.async_wait(bind(&Timer::on_tick, this, std::placeholders::_1));
    }

    void on_tick(error_code ec) {
        if (ec) {
            std::cerr << "Warning: " << ec.message() << std::endl;
            return;
        } else if (cb_()) {
            timer_.expires_at(timer_.expiry() + interval_);
            do_loop();
        }
    }
};

现在您可以像这样使用它:

#include <boost/asio.hpp>
#include <functional>
#include <iostream>
namespace asio = boost::asio;
using namespace std::chrono_literals;
using boost::system::error_code;
using duration = std::chrono::steady_clock::duration;

struct Timer {
    using Callback = std::function<bool()>;

    Timer(asio::any_io_executor ex, duration d, Callback cb)
        : timer_(ex, d)
        , interval_(d)
        , cb_(std::move(cb)) { do_loop(); }

  private:
    asio::steady_timer timer_;
    duration           interval_;
    Callback           cb_;

    void do_loop() {
        timer_.async_wait(bind(&Timer::on_tick, this, std::placeholders::_1));
    }

    void on_tick(error_code ec) {
        if (ec) {
            std::cerr << "Warning: " << ec.message() << std::endl;
            return;
        } else if (cb_()) {
            timer_.expires_at(timer_.expiry() + interval_);
            do_loop();
        }
    }
};

int main() {
    asio::io_context io;
    auto ex = io.get_executor();

    auto printer = [](std::string_view name) {
        return [name, count_ = 0]() mutable {
            bool more = count_ < 5;
            std::cout << "Printer " << quoted(name) << (more ? " " : " Last num ") << count_ << "\n";
            ++count_;
            return more;
        };
    };

    std::optional<Timer> second;

    Timer first(ex, 1s, printer("First"));
    Timer delay(ex, 1500ms, [&] {
        second.emplace(ex, 1s, printer("Second"));
        return false;
    });

    io.run();
}

看看吧 Live On Coliru

打印内容:

Printer "First" 0
Printer "First" 1
Printer "Second" 0
Printer "First" 2
Printer "Second" 1
Printer "First" 3
Printer "Second" 2
Printer "First" 4
Printer "Second" 3
Printer "First" Last num 5
Printer "Second" 4
Printer "Second" Last num 5

或者更具互动性: