Mutex assertion failed in media_list_player.c when creating new media list player

This simple LibVLC program fails with an assertion:

#include <unistd.h>
#include <vlc/vlc.h>
#include <vlc/libvlc.h>
#include <vlc/libvlc_media_list_player.h>

int main(int argc, char** argv) {

    libvlc_instance_t *p_instance = libvlc_new(0, NULL);

    libvlc_media_list_player_t *p_player = libvlc_media_list_player_new(p_instance); // <------ fails here

    libvlc_media_list_player_release(p_player);

    libvlc_release(p_instance);

}

The failure that is reported:

test: media_list_player.c:110: assert_locked: Assertion `vlc_mutex_marked(&p_mlp->mp_callback_lock)' failed.

This is the code around line 110:

static inline void assert_locked(libvlc_media_list_player_t * p_mlp)
{
    vlc_mutex_assert(&p_mlp->mp_callback_lock);       <-----
    (void) p_mlp;
}

This is called from libvlc_media_list_player_new, which eventually calls:

static void
install_media_player_observer(libvlc_media_list_player_t * p_mlp)
{
    assert_locked(p_mlp);           <-----
    libvlc_event_attach(mplayer_em(p_mlp), libvlc_MediaPlayerEndReached, media_player_reached_end, p_mlp);
}

I most recently tested this against the VLC master git at d45268d2, although this problem has been around longer than that (I'm sorry I don't recall the first time I noticed this).

OS: Linux 4.15.0-45-generic 48-Ubuntu SMP Tue Jan 29 16:28:13 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

I completely understand that the master git is undergoing continuing development, and that things might not work from time to time.

assigned to @Courmisch

commit 6a23d2cd782096110fc32a074d1083a5452fa38b
Author: Felix Paul Kühne <fkuehne@videolan.org>
Date:   Thu Sep 10 13:40:26 2015 +0200

    libvlc media list player: attach observer after player instance creation

unassigned @Courmisch

In case it wasn't clear from my initial report, this problem is not apparent in VLC 3.0.6.

Because the assertion was compiled as a no-op. The bug is actually 3+ years old.

assigned to @tguillem

fixed by 5111f5e2851a06b737e4d9c67e1839787e91ffef

added Status::fixed label

closed

After the above fix, there is a similar problem when trying to get the event manager:

static inline libvlc_event_manager_t * mplayer_em(libvlc_media_list_player_t * p_mlp)
{
    assert_locked(p_mlp); <--------- ASSERTION FAILS
    return libvlc_media_player_event_manager(p_mlp->p_mi);
}

There are other locations where assert_locked(p_mlp) is invoked that may be related.

removed Status::fixed label

reopened

Indeed, here is the additional fix 61ee1b1dab119ec31b33c022f445225a393248cb

This time, I really tested it.

added Status::fixed label

closed