Bram - Smartelectronix wrote:
> I have some tasks (in my case songs that need "rendering") which are
> executed on various amazon EC2 machines. I need to distribute each task
> to one machine only and make sure there's no concurrent rendering.
>
> I tried this:
>
[...]
> song_id = int(cursor.fetchone()[0])
>
> cursor.execute("UPDATE splice_song SET
> processing_state = 'B',
> processing_start = now()
> WHERE id = %s", [song_id])
>
[...]
>
> But, when two machines access the URL at the same time, I get this:
>
> Traceback (most recent call last):
> File "/opt/splice/pysplice/api/views.py", line 361,
> in get_song_to_process
> song_id = int(cursor.fetchone()[0])
> TypeError: 'NoneType' object is unsubscriptable
Try something like this (not tested):
song_row = cursor.fetchone()
if song_row is not None:
song_id = int(song_row[0])
cursor.execute("UPDATE splice_song SET
processing_state = 'B',
processing_start = now()
WHERE id = %s", [song_id])
> I also need to be able to signal: "all is ok, all songs have been
> rendered, take a break" in some way.
You can signal "all songs has been sent to rendering" in else section of
above if.
To signal "all songe have been rendered" you need to get some feedback
from EC2 machines.
Best regards,
Jacek.
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