[vlc-devel] [PATCH] access/qtsound: Fix race in qtsound close

[Marvin Scholz]

On 20 Jan 2019, at 10:39, David Fuhrmann wrote:

> Hi Marvin,
>
> I believe this is not a good idea: If you run a QTsound session and 
> then quit VLC, the main loop will stop before qtsound is closed, and 
> you have a deadlock.
>
> I think we need to question why this is needed at all. So far, I did 
> not find any convincing reasons or bug reports why this destruction 
> can’t be done in the same thread.
>
> AVAudioCapture is the replacement of QTsound in vlc.git, and here we 
> have the same problem. For now, I decided to just destruct everything 
> on the same thread there, and so far I see no problems with that.
>

For AVAudioCapture I don't think doing that on the main thread is 
needed.
For QTsound I have no clue, I just tried to modify the existing code to 
prevent the race,
though QTSound has some weird limitations like that it can't work 
without the macOS GUI,
iirc, so I would not be surprised...

> Best,
> David
>
>> Am 20.01.2019 um 04:36 schrieb Marvin Scholz <epirat07 at gmail.com>:
>>
>> Destruction of qtsound objects was dispatched async to the main 
>> thread,
>> this causes a race so that the qtsound objects can still be around 
>> when
>> the actual VLC objects those rely on are already gone (because Close 
>> was
>> already left), causing weird crashes.
>>
>> Ref CD 0ee7a644-041f-453d-a196-7cdd75acaf3b
>> ---
>> modules/access/qtsound.m | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/modules/access/qtsound.m b/modules/access/qtsound.m
>> index 533d6e81344..ab44e12d777 100644
>> --- a/modules/access/qtsound.m
>> +++ b/modules/access/qtsound.m
>> @@ -504,9 +504,9 @@ static void Close(vlc_object_t *p_this)
>>         demux_t *p_demux = (demux_t*)p_this;
>>         demux_sys_t *p_sys = p_demux->p_sys;
>>
>> -        [p_sys->session 
>> performSelectorOnMainThread:@selector(stopRunning) withObject:nil 
>> waitUntilDone:NO];
>> -        [p_sys->audiooutput 
>> performSelectorOnMainThread:@selector(release) withObject:nil 
>> waitUntilDone:NO];
>> -        [p_sys->session 
>> performSelectorOnMainThread:@selector(release) withObject:nil 
>> waitUntilDone:NO];
>> +        [p_sys->session 
>> performSelectorOnMainThread:@selector(stopRunning) withObject:nil 
>> waitUntilDone:YES];
>> +        [p_sys->audiooutput 
>> performSelectorOnMainThread:@selector(release) withObject:nil 
>> waitUntilDone:YES];
>> +        [p_sys->session 
>> performSelectorOnMainThread:@selector(release) withObject:nil 
>> waitUntilDone:YES];
>>
>>         free(p_sys);
>>     }
>> -- 
>> 2.17.2 (Apple Git-113)
>>
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