I've done something very similar. I control the number of concurrent child processes by simply keeping a counter of how many are active at any one time. The main loop that polls a queue will only accept new jobs if the counter is less than the configuration-defined limit.

I didn't find anything Twisted-specific to limit the number of forked processes, but it was easy to implement in my own logic.

Cheers, Chris

On 19 Sep 2007, at 11:26, 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?

Thank you

In fact the code I use to perform concurrent processing from a disk- based request queue is available here, http://www.psychofx.com/directory_queue_service/

Feedback welcome.

Cheers, Chris Miles

On 19 Sep 2007, at 11:57, Chris Miles wrote:

I've done something very similar. I control the number of concurrent child processes by simply keeping a counter of how many are active at any one time. The main loop that polls a queue will only accept new jobs if the counter is less than the configuration- defined limit.

I didn't find anything Twisted-specific to limit the number of forked processes, but it was easy to implement in my own logic.

Cheers, Chris

On 19 Sep 2007, at 11:26, 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?

Thank you

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?

Hey Daniel,

There's a semaphore convenience in twisted.internet.defer - which can be used to control the number of things which have concurrent access to .. something.

You could make that something your function which launches a system call, with something like:

s = defer.DeferredSemaphore(2) dlist = [ s.run(encodeToFormat, video, format) for format in formats] d = defer.gatherResults(dlist) return d

cheers, Andy.