boost :: asio vs. libpcap:避免两次调用close

Question

在strace以下程序上运行时:

#include <boost/asio.hpp>
#include <pcap.h>

using namespace boost;

int main(int argc, char* argv[])
{
    asio::io_service io;
    asio::posix::stream_descriptor stream(io);
    char errorBuffer[BUFSIZ];
    pcap_t* p = pcap_open_live("any", BUFSIZ, false, 0, errorBuffer);
    stream.assign(pcap_get_selectable_fd(p));
    io.run();
    stream.close();
    pcap_close(p);
    return 0;
}

我明白了:

close(6)                                = 0
setsockopt(6, SOL_PACKET, PACKET_RX_RING, {block_size=0, block_nr=0, frame_size=0, frame_nr=0}, 16) = -1 EBADF (Bad file descriptor)
munmap(0xb733c000, 4145152)             = 0
close(6)                                = -1 EBADF (Bad file descriptor)

如你所见,close在同一个fd(第一个stream.close(),然后是pcap_close(p))上调用两次.虽然程序可能没有意义,但我需要同时调用stream.close()(以防止io_service调用epoll_ctl关闭fd)和pcap_close(p)(释放由此使用的内存pcap_t) - 这发生在多线程程序上.

关于如何做到这一点的任何想法,而不是两次调用close相同的fd？

Answer 1

A posix::stream_descriptor假定描述符的所有权,它将在超出范围时关闭它.要解决双重关闭,请在分配之前复制描述符dup().