[vlc-devel] [PATCH 00/20] MR: Finishing vout life cycle work

[Thomas Guillem]

On Thu, May 9, 2019, at 13:36, Rémi Denis-Courmont wrote:
> Creation/deleting from user point of view. Meaning enable/disable at the vout window.
> 
> Furthermore, it seems rather nasty to forbid UIs from going to their mainloop when creating/destroying the (disabled) window.

Yes, you are right. I need to rework my whole branch then.

> 
> Le 9 mai 2019 14:24:54 GMT+03:00, "Rémi Denis-Courmont" <remi at remlab.net> a écrit :
>> It will still deadlock because vout_Request() and aout_DecNew() still need to be interlocked, for the same reason as Laurent put the lock in the first place. Without it, we cannot sequence outputs creation/deletion as expected.
>> 
>> Well probably it could be separate for aout and vout. But it's still needed.
>> 
>> Le 9 mai 2019 14:10:33 GMT+03:00, Thomas Guillem <thomas at gllm.fr> a écrit :
>>> I backported my "merge both locks" commit into 3.0 to reproduce the deadlock.
>>> 
>>> Indeed, it protected a deadlock when the following happened:
>>> 
>>> The GUI (Qt here) hold vouts while a vout is created from an other thread.
>>> cf. https://code.videolan.org/tguillem/vlc/snippets/955/raw for the backtrace
>>> 
>>> 1/ A decoder thread request a vout, LOCK the input_resource mutex, and create a vout
>>> 2/ The GUI is on its mainloop and WAIT the input_resource mutex.
>>> 3/ From the decoder thread, The vout_Request() load a "vout window" plugin, that will emit and wait for the getVideoSlot() that need to be executed in the GUI thread
>>> 
>>> => Deadlock
>>> 
>>> But this won't happen on VLC 4.0 (I tested it to made sure) since vout_Request() is called unlocked. Only the vout_Create() is locked, but this call only load the "vout window" plugin without enabling it.
>>> 
>>> I updated my vout-life/6 branch to fix some issues: https://code.videolan.org/tguillem/vlc/commits/vout-life/6
>>> 
>>> Mainly related to the "es_out: terminate free vout in more places" commit. The window was not disabled when I was disabled video tracks from the UI.
>>> 
>>> Also, this branch do revert a commit from Rémi: "resource: atomically return vout on failure (fixes #22284)" only to fix the issue in a diffrent way from the "resource: respect vout order" commit.
>>> 
>>> On Thu, May 9, 2019, at 12:01, Thomas Guillem wrote:
>>>> 
>>>> On Thu, May 9, 2019, at 11:52, Rémi Denis-Courmont wrote:
>>>>> No. Plugins are supposed to be reentrant, and at least the Qt window provider was before you disabled it. Besides, the resource lock cannot prevent reentry into a vout window activation callback anyway.
>>>> 
>>>> The Qt window provider is protected by the resource lock since it's created from vout_Create() that is locked. Indeed this lock is not enough since there can be several input_resource.
>>>> 
>>>>> -- 
>>>>> Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez excuser ma brièveté. 
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> 
> -- 
> Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez excuser ma brièveté. 
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