boost::asio vs. libpcap: avoid calling close twice

Question

When running strace on the following program:

#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;
}

I get:

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)

As you can see, close is called twice on the same fd (first by stream.close(), then by pcap_close(p)). While the program might not make sense, I need to call both stream.close() (to prevent io_service from calling epoll_ctl on a closed fd) and pcap_close(p) (to release the memory used by the pcap_t) - this happens on a multithreaded program.

Any ideas on how to do this without calling close on the same fd twice?

Answer 1

A posix::stream_descriptor assumes ownership of the descriptor, it will close it when going out of scope. To resolve the double close, duplicate the descriptor before assigning with dup().