The VideoLAN Forums

Posted: **09 Jan 2009 15:04**

Hello,

I try to play 2 videos on vlc086e (win32 libvlc) with vmem plugin,
I create new instance/play 1st video => OK
I createnew instance/play 2nd video => OK
I stop and destroy correctly my 1st instance,
but libvlc_destroy() crash on my 2nd instance.
If I create/destroy 2 videos sequentially, no problem !

Any idea ?
Thank you

I m using those args :

Code: Select all

        "--no-one-instance",
        "--loop",
        "--no-stats",
        "--intf", "dummy",
        "--fast-mutex", "--win9x-cv-method=1",
        "--plugin-path=.\\VLCplugins",
        "--vout", "vmem",
        "--vmem-width", pwidth,
        "--vmem-height", pheight,
        "--vmem-pitch", ppitch,
        "--vmem-chroma", "RV16",
        "--vmem-lock", plock,
        "--vmem-unlock", punlock,
        "--vmem-data", pdata,

Posted: **09 Jan 2009 15:53**

beware of multiple instances of libvlc ! They are not independent.

A new libvlc instance overwrites options passed to a previous one. In the case of vmem, some of these options are pointers to functions So you can very easily end up with a crash.

Posted: **09 Jan 2009 16:55**

Thank you erwan10 for your response,

If I understand there is 1 risk when using config_GetPsz()
but config_GetPsz() is only called in Init() of vmem and args are copied into
instance datas ...
so I do not see the impact on libvlc_destroy().

vmem source code part :

Code: Select all

struct vout_sys_t
{
    int i_width, i_height, i_pitch;

    void * (*pf_lock) (void *);
    void (*pf_unlock) (void *);
    void *p_data;
};

static int Create( vlc_object_t *p_this )
{
    vout_thread_t *p_vout = ( vout_thread_t * )p_this;

    /* Allocate instance and initialize some members */
    p_vout->p_sys = malloc( sizeof( vout_sys_t ) );
. . .

static int Init( vout_thread_t *p_vout )
{
. . .
    psz_tmp = config_GetPsz( p_vout, "vmem-lock" );
    p_vout->p_sys->pf_lock = (void * (*) (void *))(intptr_t)atoll( psz_tmp );
    free( psz_tmp );
. . .

static void Destroy( vlc_object_t *p_this )
{
    vout_thread_t *p_vout = ( vout_thread_t * )p_this;

    /* Destroy structure */
    free( p_vout->p_sys );
}

I tried the same test without using vmem and I found an interesting think :
when I compile/link on cygwin => OK
when I compile/link with VisualStudio2005 => libvlc_destroy() crashes on 2nd call

After some investigations, I found crash in 2nd call to libvlc_destroy() occurs in VLCsources/misc/messages.c

Code: Select all

void __msg_Destroy( vlc_object_t *p_this )
{
    int i;
    for( i = p_this->p_libvlc->msg_bank.i_queues -1 ; i >= 0;  i-- )
    {
...
    }
    vlc_mutex_destroy( &(p_this->p_libvlc->msg_bank.lock) );   <= this lock in libvlc context is maybe already freed !!
}

Posted: **12 Jan 2009 11:43**

In libvlc.c, we only create the Msg queue on 1st call to VLC_Create(), but when calling VLC_Destroy() we systematically destroy the Msg queue, can someone confirm there is 1 bug here ?

Code: Select all

int VLC_Create( void )
{
...
    if( !libvlc.b_ready )
    {
...
        /* Initialize message queue */
        msg_Create( p_libvlc );
...
        libvlc.b_ready = VLC_TRUE;
    }

int VLC_Destroy( int i_object )
{
...
    /*
     * System specific cleaning code
     */
    system_End( p_vlc );

    /*
     * Free message queue.
     * Nobody shall use msg_* afterward.
     */
    msg_Flush( p_vlc );
    msg_Destroy( p_libvlc );
...
}

Sorry for this double-post, just want some expert help

Thank you

The VideoLAN Forums

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