[Twisted-Python] Control the number of parallel system calls

[Andrew Bennetts]

Daniel de la Cuesta wrote:
> Hi,
> 
> I am developing a video conversion server. To process the video conversion I
> use the method "getProcessOutput" to call "ffmpeg".
> 
> The user upload the video using a HTTP POST and each video must be converted to
> 8 or 10 output formats.
> 
> Currently, all the conversions for each video are processed in parallel, what I
> want to do is to control the number of parallel system calls to "ffmpeg". For
> example I only want 2 processes at the same time and when one of them finishes
> the next process start.
> 
> How can I do that?
> 
> Is there any function in Twisted that implements that?

The obvious way to do that would be using a
twisted.internet.defer.DeferredSemaphore.

-Andrew.