Multiple threads

[Thomas Rachel]

Am 16.11.2011 14:48 schrieb Eduardo Oliva:
> Hello, I have a py script that reads for all "m2ts" video files and convert them to "mpeg" using ffmpeg with command line.
>
> What I want to do is:
>
>    I need my script to run 2 separated threads, and then when the first has finished, starts the next one....but no more than 2 threads.
>    I know that Semaphores would help with that.
>    But the problem here is to know when the thread has finished its job, to release the semaphore and start another thread.
>
> Any help would be great.

I'm not sure if you need threads at all: if you launch a process with 
subprocess, it runs and you only would have to wait() for it. The same 
can be done with two processes.

Pseudocode:

LIMIT = 2

processes = []


def do_waiting(limit):
     while len(processes) >= limit:
         % take the first one...
         sp = processes.pop(0)
         % wait for it...
         st = sp.wait(100)
         if is None:
             % timeout, not finished yet, push back.
             processes.append(sp)
         else:
             % finished - don't push back, let outer for loop continue.
             print sp, "has finished with", st

for fname in list:
     % launch process ...
     sp = subprocess.Popen(...)
     % ... and register it.
     processes.append(sp)
     % If we are on the limit, wait for process to finish.
     do_waiting(LIMIT)

do_waiting(1)


Thomas