使用boost：ASIO与选择？阻塞TCP输入或文件更新 [英] using boost:asio with select? blocking on TCP input OR file update

问题描述

我本来打算在我的程序中的线程这将等待两个文件描述符，一个插座，第二个为FD描述文件系统（特别是等着看是否有新的文件被添加到一个目录）。因为我希望很少看到任何新文件添加或在我即将到来的新的TCP消息想有一个线程等待任何一个输入和处理任何输入时，它occures而不是有独立的线程困扰检测。

I had intended to have a thread in my program which would wait on two file descriptors, one for a socket and a second one for a FD describing the file system (specifically waiting to see if a new file is added to a directory). Since I expect to rarely see either the new file added or new TCP messages coming in I wanted to have one thread waiting for either input and handle whichever input is detected when it occures rather then bothering with seperate threads.

然后我（终于！）获准从老板使用boost。所以现在我想更换提振基本插槽：ASIO。只有我遇到一个小问题。这似乎是ASIO的形式实现它自己的选择的版本而不是提供一个FD我可以选择直接使用。这使我不确定我怎么能在这两种情况下，新的文件和TCP输入块，在同一时间，当一个只选择工作以及其他似乎并不支持使用选择。有一个简单的工作，围绕这个我失踪？

I then (finally!) got permission from the 'boss' to use boost. So now I want to replace the basic sockets with boost:asio. Only I'm running into a small problem. It seems like asio implimented it's own version of select rather then providing a FD I could use with select directly. This leaves me uncertain how I can block on both conditions, new file and TCP input, at the same time when one only works with select and the other doesn't seem to support the use of select. Is there an easy work around to this I'm missing?

推荐答案

ASIO最好异步使用（这是它代表什么）：你可以设置处理程序为TCP读取和文件描述符活动，以及处理程序会叫你。

ASIO is best used asynchronously (that's what it stands for): you can set up handlers for both TCP reads and the file descriptor activity, and the handlers would be called for you.

下面是让你开始（与inotify的支持书面Linux）的演示例如：

Here's a demo example to get you started (written for Linux with inotify support):

#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <sys/inotify.h>

namespace asio = boost::asio;
void start_notify_handler();
void start_accept_handler();

// this stuff goes into your class, only global for the simplistic demo
asio::streambuf buf(1024);
asio::io_service io_svc;
asio::posix::stream_descriptor stream_desc(io_svc);
asio::ip::tcp::socket sock(io_svc);
asio::ip::tcp::endpoint end(asio::ip::tcp::v4(), 1234);
asio::ip::tcp::acceptor acceptor(io_svc, end);

// this gets called on file system activity
void notify_handler(const boost::system::error_code&,
                    std::size_t transferred)
{
    size_t processed = 0;
    while(transferred - processed >= sizeof(inotify_event))
    {
        const char* cdata = processed
                            + asio::buffer_cast<const char*>(buf.data());
        const inotify_event* ievent =
                                 reinterpret_cast<const inotify_event*>(cdata);
        processed += sizeof(inotify_event) + ievent->len;
        if(ievent->len > 0 && ievent->mask & IN_OPEN)
            std::cout << "Someone opened " << ievent->name << '\n';
    }
    start_notify_handler();
}

// this gets called when nsomeone connects to you on TCP port 1234
void accept_handler(const boost::system::error_code&)
{
    std::cout << "Someone connected from " 
              << sock.remote_endpoint().address() << '\n';
    sock.close(); // dropping connection: this is just a demo
    start_accept_handler();
}

void start_notify_handler()
{
    stream_desc.async_read_some( buf.prepare(buf.max_size()),
        boost::bind(&notify_handler, asio::placeholders::error,
                    asio::placeholders::bytes_transferred));
}

void start_accept_handler()
{
    acceptor.async_accept(sock,
        boost::bind(&accept_handler, asio::placeholders::error));
}

int main()
{
    int raw_fd = inotify_init(); // error handling ignored
    stream_desc.assign(raw_fd);
    inotify_add_watch(raw_fd, ".", IN_OPEN);
    start_notify_handler();
    start_accept_handler();
    io_svc.run();
}

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