[zeromq-dev] FD resource leak when opening and closing an inproc socket

[Itay Chamiel]

Hi, we have a client thread that is supposed to receive data from a parent
thread, then disconnect when done. We've noticed that when the socket is
closed there's a leak of an eventfd (file descriptor), therefore we have a
leak every time such a client is created and destroyed - even if no data is
transferred.

Here is a quick C++ program to reproduce it. I'm running on a Ubuntu 18
desktop with ZMQ 4.1.6 or 4.3.3. This loop is expected to run forever but
crashes a little after 1000 iterations due to too many open files.

#include "zmq.hpp"

int main() {
  zmq::context_t context;
  while(1) {
    zmq::socket_t* socket = new zmq::socket_t(context, ZMQ_SUB);
    socket->connect("inproc://some_name");
    delete socket;
  }
}

The problem does not occur for other connection types (i.e. replace inproc
with ipc and the problem will not occur).
In case you want it without the C++ bindings, here is a slightly more
elaborate C example which also sets LINGER to zero (with no effect) and
displays the number of FDs in use by the process each iteration.

#include <zmq.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
  void* ctx = zmq_ctx_new();
  for (int i=0; ; i++) {
    void* zmq_sock = zmq_socket(ctx, ZMQ_SUB);
    if (!zmq_sock) { printf("fail after %d iterations: %s\n", i,
zmq_strerror(errno)); exit(-1); }
    int linger = 0;
    int rc = zmq_setsockopt(zmq_sock, ZMQ_LINGER, &linger, sizeof(linger));
// this doesn't actually help
    if (rc != 0) exit(-1);
    rc = zmq_connect(zmq_sock, "inproc://some_name");
    if (rc != 0) exit(-1);
    rc = zmq_close(zmq_sock);
    if (rc != 0) exit(-1);
    // show the number of used FDs
    char cmd[100];
    sprintf(cmd, "ls -l -v /proc/%d/fd | wc -l", (int)getpid());
    system(cmd);
    // test is hard to abort without a sleep
    usleep(100*1000);
  }
}

Thank you,

Itay Chamiel, OrCam
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