Question

我有一个程序，希望通过发送SIGINT将某些数据写入文件而不是立即退出来阻止它。但是，如果程序的用户再次发送SIGINT，则程序应立即退出并忘记将数据写入文件。

出于便携性原因，我想将boost::asio用于此目的。

我的初始（简化）方法（见下文）不起作用。这是不可能的还是我错过了什么？

处理程序似乎只被调用一次（打印出消息），当循环达到最大迭代次数时程序总是停止。

void handler(
const boost::system::error_code& error,
int signal_number) {
    if (!error) {
        static bool first = true;
        if(first) {
            std::cout << " A signal(SIGINT) occurred." << std::endl;
            // do something like writing data to a file
            first = false;
        }
        else {
            std::cout << " A signal(SIGINT) occurred, exiting...." << std::endl;
            exit(0);
        }
    }
}

int main() {
    // Construct a signal set registered for process termination.
    boost::asio::io_service io;
    boost::asio::signal_set signals(io, SIGINT);

    // Start an asynchronous wait for one of the signals to occur.
    signals.async_wait(handler);
    io.run();
    size_t i;

    for(i=0;i<std::numeric_limits<size_t>::max();++i){
        // time stepping loop, do some computations
    }

    std::cout << i << std::endl;
    return 0;
}

Answer 1

处理完第一个事件后，您不会在服务对象上发布任何新工作，因此它会退出。

这意味着然后（在ioservice退出之后）启动紧密循环。这可能不是您的预期。

如果您想再次侦听SIGINT，则必须再次从处理程序中等待信号集：

#include <boost/asio.hpp>
#include <boost/asio/signal_set.hpp>
#include <boost/bind.hpp>
#include <boost/atomic.hpp>
#include <iostream>

void handler(boost::asio::signal_set& this_, boost::system::error_code error, int signal_number) {
    if (!error) {
        static boost::atomic_bool first(true);
        if(first) {
            // do something like writing data to a file
            std::cout << " A signal(SIGINT) occurred." << std::endl;
            first = false;

            this_.async_wait(boost::bind(handler, boost::ref(this_), _1, _2));
        }
        else {
            std::cout << " A second signal(SIGINT) occurred, exiting...." << std::endl;
            exit(1);
        }
    }
}

int main() {
    // Construct a signal set registered for process termination.
    boost::asio::io_service io;
    boost::asio::signal_set signals(io, SIGINT);

    // Start an asynchronous wait for one of the signals to occur.
    signals.async_wait(boost::bind(handler, boost::ref(signals), _1, _2));
    io.run();
    return 2;
}

正如您所看到的，我将signal_set&引用绑定到处理程序，以便在收到第一个信号后能够async_wait。另外，作为一个原则问题，我将first设为原子（尽管在多个线程上运行io_service之前没有必要）。

您真的希望在后台运行io_service吗？在这种情况下，让它看起来像这样：

signals.async_wait(boost::bind(handler, boost::ref(signals), _1, _2));

boost::thread(boost::bind(&boost::asio::io_service::run, boost::ref(io))).detach();

while (true)
{
    std::cout << "Some work on the main thread...\n";
    boost::this_thread::sleep_for(boost::chrono::seconds(1));
}

具有典型输出：

Some work on the main thread...
Some work on the main thread...
Some work on the main thread...
^CSome work on the main thread...
 A signal(SIGINT) occurred.
Some work on the main thread...
Some work on the main thread...
^CSome work on the main thread...
 A second signal(SIGINT) occurred, exiting....

boost :: asio signal_set处理程序仅在捕获到第一个信号后执行，并忽略相同类型的连续信号

1 个答案: