[vlc-devel] [PATCH] libvlc: dump object types abd names when leaking

[Alexandre Janniaux]

Hi,

I think that not being universally correct is not a problem for a
debugging tool. I find this patch quite useful, especially for windows
and beginner developer in the project, and would be a good addition to
ASan debugging.

If universality is a blocking issue, it could be activated with a
--with-sanitizer=vlcobject like parameter.

On 2019-02-21 11:18, Rémi Denis-Courmont wrote:
> Hi,
> 
> Well I did debug that assertion failure using (ASan +) gdb just fine
> last time. The code has not changed. So this kludge is definitely not
> necessary for its alleged purpose.
> 
> Not only that but stderr is not universally the output for debug nor
> is it universally where assertion failures are dumped to, so this
> patch does not even work properly
> 
> And in most cases you can see the leak by stopping all inputs and
> dumping the objects tree before quitting, anyway.
> 
> Le 21 février 2019 11:24:57 GMT+02:00, Thomas Guillem <thomas at gllm.fr> 
> a écrit :
>> Comment:
>> A lot of developers asked me to propose this patch again. It was
>> previously
>> refused because developers could use proper debugging tools. I 
>> disagree
>> with
>> that assumption. Even with Asan, when the leak assert fail, it will
>> abort()
>> without prompting any leaks, so you'll have to edit libvlc.c to remove
>> this
>> assert. If your leak was not reproducible, you'll lose a precious
>> information.
>> And good luck finding the leak with GDB, you really need to know the
>> internal
>> of vlc_object_t to iterate through the different list to get the
>> culprit.
>> 
>> Commit log:
>> 
>> In case of a vlc_object_t leak, and if asserts are enabled, the error
>> output
>> will be like the following (when leaking intentionally decoder_t
>> objects):
>> 
>> === vlc_object LEAKS detected ===
>>  \ playlist
>>  |   \ input
>>  |   |   \ decoder avcodec
>>  |   |   | decoder faad
>>  |   |   | decoder stl
>> ---
>> src/libvlc.c | 30 ++++++++++++++++++++++++++++++
>> 1 file changed, 30 insertions(+)
>> 
>> diff --git a/src/libvlc.c b/src/libvlc.c
>> index 8e8d2ca8b2..d9ff96de84 100644
>> --- a/src/libvlc.c
>> +++ b/src/libvlc.c
>> @@ -436,6 +436,24 @@ void libvlc_InternalCleanup( libvlc_int_t
>> *p_libvlc )
>> #endif
>> }
>> 
>> +#ifndef NDEBUG
>> +static void DumpObjectLeaks(vlc_object_internals_t *priv, unsigned
>> level)
>> +{
>> +    bool first = true;
>> +    vlc_list_foreach(priv, &priv->children, siblings)
>> +    {
>> +        vlc_object_t *obj = vlc_externals(priv);
>> +        for (unsigned i = 0; i < level; i++)
>> +            fprintf(stderr, "  %s ", first && i == level -1 ? "\\" :
>> "|");
>> +        char *name = vlc_object_get_name(obj);
>> +        fprintf(stderr, "%s %s\n", vlc_object_typename(obj), name ?
>> name : "");
>> +        free(name);
>> +        DumpObjectLeaks(priv, level + 1);
>> +        first = false;
>> +    }
>> +}
>> +#endif
>> +
>> /**
>>  * Destroy everything.
>> * This function requests the running threads to finish, waits for 
>> their
>> @@ -449,6 +467,18 @@ void libvlc_InternalDestroy( libvlc_int_t
>> *p_libvlc )
>> 
>>     vlc_ExitDestroy( &priv->exit );
>> 
>> +#ifndef NDEBUG
>> +    {
>> +        vlc_object_internals_t *internal = vlc_internals(p_libvlc);
>> +        if (atomic_load(&internal->refs) != 1)
>> +        {
>> +            vlc_mutex_lock(&internal->tree_lock);
>> +            fprintf(stderr, "=== vlc_object LEAKS detected ===\n");
>> +            DumpObjectLeaks(internal, 1);
>> +            vlc_mutex_unlock(&internal->tree_lock);
>> +        }
>> +    }
>> +#endif
>>     assert( atomic_load(&(vlc_internals(p_libvlc)->refs)) == 1 );
>>     vlc_object_release( p_libvlc );
>> }
>> --
>> 2.20.1
>> 
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