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

[Rémi Denis-Courmont]

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.

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.
>>> 
>>>> -- 
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>-- 
>Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez excuser
>ma brièveté.

-- 
Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez excuser ma brièveté.
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