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

Answer 1

I finally figured out how to stop a loop and clean up all handles. I created a bunch of handles and SIGINT signal handle:

uv_signal_t *sigint = new uv_signal_t;
uv_signal_init(uv_default_loop(), sigint);
uv_signal_start(sigint, on_sigint_received, SIGINT);

When SIGINT is received (Ctrl+C in console is pressed) the on_sigint_received callback is called. The on_sigint_received looks like:

void on_sigint_received(uv_signal_t *handle, int signum)
{
    int result = uv_loop_close(handle->loop);
    if (result == UV_EBUSY)
    {
        uv_walk(handle->loop, on_uv_walk, NULL);
    }
}

It triggers a call back function on_uv_walk:

void on_uv_walk(uv_handle_t* handle, void* arg)
{
    uv_close(handle, on_uv_close);
}

It tries to close each opened libuv handle. Note: that I do not call uv_stop before uv_walk, as mentioned saghul. After on_sigint_received function is called libuv loop continuous the execution and on the next iteration calls on_uv_close for each opened handle. If you call the uv_stop function, then the on_uv_close callback will not be called.

void on_uv_close(uv_handle_t* handle)
{
    if (handle != NULL)
    {
        delete handle;
    }
}

After that libuv do not have opened handles and finishes the loop (exits from uv_run):

uv_run(uv_default_loop(), UV_RUN_DEFAULT);
int result = uv_loop_close(uv_default_loop());
if (result)
{
    cerr << "failed to close libuv loop: " << uv_err_name(result) << endl;
}
else
{
    cout << "libuv loop is closed successfully!\n";
}

Answer 2

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