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

[Ed Suominen]

Andrew Bennetts wrote:
> 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.

Or http://foss.eepatents.com/AsynQueue ... :-)