----------------------------------------
> Date: Mon, 20 May 2013 18:35:20 +1000
> From: c...@zip.com.au
> To: carlosnepomuc...@outlook.com
> CC: python-list@python.org
> Subject: Re: Please help with Threading
>
> On 20May2013 10:53, Carlos Nepomuceno <carlosnepomuc...@outlook.com> wrote:
> | I just got my hands dirty trying to synchronize Python prints from many
> threads.
> | Sometimes they mess up when printing the newlines.
> | I tried several approaches using threading.Lock and Condition.
> | None of them worked perfectly and all of them made the code sluggish.
>
> Show us some code, with specific complaints.
>
> Did you try this?
>
> _lock = Lock()
>
> def lprint(*a, **kw):
> global _lock
> with _lock:
> print(*a, **kw)
>
> and use lprint() everywhere?
It works! Think I was running the wrong script...
Anyway, the suggestion you've made is the third and latest attempt that I've
tried to synchronize the print outputs from the threads.
I've also used:
### 1st approach ###
lock = threading.Lock()
[...]
try:
lock.acquire()
[thread protected code]
finally:
lock.release()
### 2nd approach ###
cond = threading.Condition()
[...]
try:
[thread protected code]
with cond:
print '[...]'
### 3rd approach ###
from __future__ import print_function
def safe_print(*args, **kwargs):
global print_lock
with print_lock:
print(*args, **kwargs)
[...]
try:
[thread protected code]
safe_print('[...]')
Except for the first one all kind of have the same performance. The
problem was I placed the acquire/release around the whole code block,
instead of only the print statements.
Thanks a lot! ;)
> For generality the lock should be per file: the above hack uses one
> lock for any file, so that's going to stall overlapping prints to
> different files; inefficient.
>
> There are other things than the above, but at least individual prints will
> never overlap. If you have interleaved prints, show us.
>
> | Is there a 100% sure method to make print thread safe? Can it be fast???
>
> Depends on what you mean by "fast". It will be slower than code
> with no lock; how much would require measurement.
>
> Cheers,
> --
> Cameron Simpson <c...@zip.com.au>
>
> My own suspicion is that the universe is not only queerer than we suppose,
> but queerer than we *can* suppose.
> - J.B.S. Haldane "On Being the Right Size"
> in the (1928) book "Possible Worlds"
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