>>>>> Vincent Gulinao <vincent.guli...@gmail.com> (VG) wrote:
>VG> lst = list()
>VG> (lst populated by async twisted deferred callbacks)
>VG> while True:
>VG> if len(lst) == SOME_NUMBER:
>VG> return lst
>VG> Q1: is this a common OK practice? I'm worried infinite loops hogs memory.
>VG> Q2: operating on list from threads (mostly appends) must be safe,
>VG> right (synchronization)?
I am not familiar enough with twisted, but I think the principle is
independent from twisted.
This loop will not hog memory but it will hog CPU time.
You should use a synchronisation construct like threading.Condition or a
Semaphore. Here is my suggestion with a Condition:
Global somewhere:
lst_cond = Condition()
In your loop:
lst = list() # Why not lst = []?
while True: # strange while/if combo
if len(lst) == SOME_NUMBER:
return lst
Make that:
with lst_cond:
while len(lst) < SOME_NUMBER:
lst_cond.wait()
return lst
In the callback:
with lst_cond:
lst.append(new_value)
lst_cond.notify()
In case you don't have a python that supports the with statement (not
even `from future') you should use:
lst_cond.acquire()
try:
.....
finally:
lst_cond.release()
I think the solution with a semaphore is less elegant.
global: sem = Semaphore()
loop:
for i in range(SOME_NUMBER):
sem.acquire()
return lst
In callback:
lst.append(new_value)
sem.release()
*Be careful: I haven't tested this code (not even syntax checked). So
consider it pseudo code.*
--
Piet van Oostrum <p...@cs.uu.nl>
URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4]
Private email: p...@vanoostrum.org
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