[osg-users] FFmpegImageStream thread safety

[OpenSceneGraph Users]

Hi Rob,

Thanks for the link.
In this version I also see that m_pImgStream->setImage is invoked
in FFmpegRenderThread::run(), another thread.
2015 is a long time ago, but do you perhaps remember why this is safe ?

Thanks in advance.

Cheers,

Ben

Op ma 10 aug. 2020 om 23:03 schreef Rob Spearman <rob at digitaliseducation.com
>:

> We made changes back in 2015 to fix threading issues with the osg ffmpeg
> plugin.  I don't think these changes ever made it into OSG.
>
> Source repo:  https://bitbucket.org/digitalis/osg-ffmpeg-plugin/
>
> On Monday, August 10, 2020 at 3:46:32 AM UTC-7 bjs.me... at gmail.com wrote:
>
>> Hi Robert,
>>
>> Thanks for your response.
>>
>> If FFmpegImageStream::publishNewFrame is invoked from a separate thread.
>> Is it then somehow guaranteed that (for example) Texture2D::apply is not
>> using/reading from the image object, while
>> FFmpegImageStream::publishNewFrame is modifying it ?
>>
>> Cheers,
>>
>> Ben
>>
>> Op vr 31 jul. 2020 om 21:24 schreef Robert Osfield <robert.... at gmail.com
>> >:
>>
>>> Hi Ben,
>>>
>>> I'm away from my dev computer so just commenting off the top of my.
>>> FFmpegImageStream should be double buffered so that the ffmpeg thread
>>> writing to the image will be writing to one part of the data, while the
>>> other half is available to be read by the graphics thread.  This should
>>> avoid threading issues.
>>>
>>> The threading used by the ffmpeg plugin is separate from the viewer
>>> threading so settings related to the viewer won't be important, nor will
>>> general settings of the scene graph.
>>>
>>> You should be able to just add the ffmpeg genearted imagestream to a
>>> texture, start the steam going and then largely forget about it.
>>>
>>> Robert.
>>>
>>> On Friday, 31 July 2020 at 20:15:45 UTC+1 bjs.me... at gmail.com wrote:
>>>
>>>> Hi,
>>>>
>>>> I was just looking at FFmpegImageStream, I am not very familiar with
>>>> this code, but I have some questions.
>>>>
>>>> It is not immediately clear to me how
>>>> FFmpegImageStream::publishNewFrame is thread safe.
>>>> It seems like the image data is set (setImage) from the video decoder
>>>> thread.
>>>> The image then uses a pointer to one of the buffers of the video
>>>> decoder (of which the contents might also change ?).
>>>>
>>>> FFmpegImageStream also doesn't seem to override requiresUpdateCall,
>>>> which I believe will result in the texture not being dynamic
>>>> (Texture2D::setImage).
>>>> Which could be used, for example in StateSet::computeDataVariance(), to
>>>> determine whether the StateSet should be dynamic (which is needed for
>>>> multithreaded rendering).
>>>>
>>>> If anyone could shed more light on this subject, it would be very much
>>>> appreciated.
>>>>
>>>> Thank you.
>>>>
>>>> Cheers,
>>>>
>>>> Ben
>>>>
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