[vlc-devel] [RFC] [NOT FOR MERGE] objres: add mutex support

[Steve Lhomme]

On 2020-01-29 8:37, Thomas Guillem wrote:
> Hello,
> 
> I would prefer to avoid using a pointer to access a mutex.
> 
> We will end up with modules using vlc_mutex_lock(sys->lock) and vlc_mutex_lock(&sys->lock).
> I think it will add more confusions.

How about vlc_obj_mutex_new(vlc_object_t *, vlc_mutex_t *)

The structure storage wouldn't be created (as it is now) and the mutex 
is accessed the same way as before.

> On Tue, Jan 28, 2020, at 21:30, Rémi Denis-Courmont wrote:
>> This adds a function to allocate a mutex that automatically gets
>> destroyed when a module fails or terminates.
>>
>> I have very mixed feelings about this, as it introduces an error return
>> where there is normally none, i.e., from vlc_mutex_init(). It also
>> requires tedious rework to replace `vlc_mutex_t' with `vlc_mutex_t *'.
>>
>> For reference, kernel code entirely solves this conundrum by not
>> requiring explicit mutex destruction (a kernel mutex does not hold any
>> resource besides its own `struct mutex' storage space). This could also
>> be done, but with significant reworking of the VLC threading layer and
>> prevents reliable detection of attempt to delete a still-in-use mutex.
>> ---
>>   include/vlc_objects.h |  2 ++
>>   src/misc/objres.c     | 15 +++++++++++++++
>>   2 files changed, 17 insertions(+)
>>
>> diff --git a/include/vlc_objects.h b/include/vlc_objects.h
>> index 19ee5207fc..32f23abf41 100644
>> --- a/include/vlc_objects.h
>> +++ b/include/vlc_objects.h
>> @@ -295,5 +295,7 @@ VLC_API VLC_MALLOC char
>> *vlc_obj_strdup(vlc_object_t *obj, const char *str);
>>    */
>>   VLC_API void vlc_obj_free(vlc_object_t *obj, void *ptr);
>>   
>> +VLC_API VLC_MALLOC vlc_mutex_t *vlc_obj_mutex_new(vlc_object_t *obj);
>> +
>>   /** @} */
>>   /** @} */
>> diff --git a/src/misc/objres.c b/src/misc/objres.c
>> index cac8624e7e..383dd760a8 100644
>> --- a/src/misc/objres.c
>> +++ b/src/misc/objres.c
>> @@ -174,3 +174,18 @@ void vlc_obj_free(vlc_object_t *obj, void *ptr)
>>   {
>>       vlc_objres_remove(obj, ptr, ptrcmp);
>>   }
>> +
>> +static void mutex_release(void *data)
>> +{
>> +    vlc_mutex_destroy(data);
>> +}
>> +
>> +vlc_mutex_t *vlc_obj_mutex_new(vlc_object_t *obj)
>> +{
>> +    vlc_mutex_t *mtx = vlc_objres_new(sizeof (*mtx), mutex_release);
>> +    if (mtx != NULL) {
>> +        vlc_mutex_init(mtx);
>> +        vlc_objres_push(obj, mtx);
>> +    }
>> +    return mtx;
>> +}
>> -- 
>> 2.25.0
>>
>> _______________________________________________
>> vlc-devel mailing list
>> To unsubscribe or modify your subscription options:
>> https://mailman.videolan.org/listinfo/vlc-devel
> _______________________________________________
> vlc-devel mailing list
> To unsubscribe or modify your subscription options:
> https://mailman.videolan.org/listinfo/vlc-devel
>