Closing libUV Handles Correctly

Question

I'm trying to find out how to fix these memory leaks I'm getting while running this program with Valgrind. The leaks occur with the two allocations in nShell_client_main. But I'm not sure how to properly free them.

I've tried freeing them at nShell_Connect, but it's causing libUV to abort the program. I've tried freeing them at the end of nShell_client_main, but then I get read/write errors when closing the loop. Does anyone know how I'm supposed to close these handles? I've read this, which got me started. But, it seams out-dated because uv_ip4_addr has a different prototype in the latest version.

(nShell_main is the "entry" point)

#include "nPort.h"
#include "nShell-main.h"

void nShell_Close(
    uv_handle_t * term_handle
){
}

void nShell_Connect(uv_connect_t * term_handle, int status){
    uv_close((uv_handle_t *) term_handle, 0);
}

nError * nShell_client_main(nShell * n_shell, uv_loop_t * n_shell_loop){

    int uv_error = 0;

    nError * n_error = 0;

    uv_tcp_t * n_shell_socket = 0;
    uv_connect_t * n_shell_connect = 0;

    struct sockaddr_in dest_addr;

    n_shell_socket = malloc(sizeof(uv_tcp_t));

    if (!n_shell_socket){
        // handle error
    }

    uv_error = uv_tcp_init(n_shell_loop, n_shell_socket);

    if (uv_error){
        // handle error
    }

    uv_error = uv_ip4_addr("127.0.0.1", NPORT, &dest_addr);

    if (uv_error){
        // handle error
    }

    n_shell_connect = malloc(sizeof(uv_connect_t));

    if (!n_shell_connect){
        // handle error
    }

    uv_error = uv_tcp_connect(n_shell_connect, n_shell_socket, (struct sockaddr *) &dest_addr, nShell_Connect);

    if (uv_error){
        // handle error
    }

    uv_error = uv_run(n_shell_loop, UV_RUN_DEFAULT);

    if (uv_error){
        // handle error
    }

    return 0;
}

nError * nShell_loop_main(nShell * n_shell){

    int uv_error = 0;

    nError * n_error = 0;

    uv_loop_t * n_shell_loop = 0;

    n_shell_loop = malloc(sizeof(uv_loop_t));

    if (!n_shell_loop){
        // handle error
    }

    uv_error = uv_loop_init(n_shell_loop);

    if (uv_error){
        // handle error
    }

    n_error = nShell_client_main(n_shell, n_shell_loop);

    if (n_error){
        // handle error
    }

    uv_loop_close(n_shell_loop);
    free(n_shell_loop);

    return 0;
}

The assertion is happening at the end of the switch statement in this excerpt of code (taken from Joyent's libUV page on Github):

void uv_close(uv_handle_t* handle, uv_close_cb close_cb) {
  assert(!(handle->flags & (UV_CLOSING | UV_CLOSED)));

  handle->flags |= UV_CLOSING;
  handle->close_cb = close_cb;

  switch (handle->type) {
  case UV_NAMED_PIPE:
    uv__pipe_close((uv_pipe_t*)handle);
    break;

  case UV_TTY:
    uv__stream_close((uv_stream_t*)handle);
    break;

  case UV_TCP:
    uv__tcp_close((uv_tcp_t*)handle);
    break;

  case UV_UDP:
    uv__udp_close((uv_udp_t*)handle);
    break;

  case UV_PREPARE:
    uv__prepare_close((uv_prepare_t*)handle);
    break;

  case UV_CHECK:
    uv__check_close((uv_check_t*)handle);
    break;

  case UV_IDLE:
    uv__idle_close((uv_idle_t*)handle);
    break;

  case UV_ASYNC:
    uv__async_close((uv_async_t*)handle);
    break;

  case UV_TIMER:
    uv__timer_close((uv_timer_t*)handle);
    break;

  case UV_PROCESS:
    uv__process_close((uv_process_t*)handle);
    break;

  case UV_FS_EVENT:
    uv__fs_event_close((uv_fs_event_t*)handle);
    break;

  case UV_POLL:
    uv__poll_close((uv_poll_t*)handle);
    break;

  case UV_FS_POLL:
    uv__fs_poll_close((uv_fs_poll_t*)handle);
    break;

  case UV_SIGNAL:
    uv__signal_close((uv_signal_t*) handle);
    /* Signal handles may not be closed immediately. The signal code will */
    /* itself close uv__make_close_pending whenever appropriate. */
    return;

  default:
    assert(0); // assertion is happening here
  }

  uv__make_close_pending(handle);
}

I could call uv__tcp_close manually, but it's not in the public headers (and probably not the right solution anyway).

Answer 1

libuv is not done with a handle until it's close callback is called. That is the exact moment when you can free the handle.

I see you call uv_loop_close, but you don't check for the return value. If there are still pending handles, it will return UV_EBUSY, so you should check for that.

If you want to close a loop and close all handles, you need to do the following:

• Use uv_stop to stop the loop
• Use uv_walk and call uv_close on all handles which are not closing
• Run the loop again with uv_run so all close callbacks are called and you can free the memory in the callbacks
• Call uv_loop_close, it should return 0 now