atomic increment

[Alexandru Mosoi]

how can i do an atomic read+increment? something like

with lock:
old = atomic_int
atomic_int += 1

but in one operation

[Diez B. Roggisch]

Re: atomic increment

Alexandru Mosoi wrote:

how can i do an atomic read+increment? something like
>
with lock:
old = atomic_int
atomic_int += 1
>
but in one operation

As above - the lock (under the assumption that it is actually a
threading.Lock) will ensure that.

Diez

[Frank Millman]

Re: atomic increment

On Aug 26, 5:56 pm, "Diez B. Roggisch" <de...@nospam.w eb.dewrote:

Alexandru  Mosoi wrote:

how can i do an atomic read+increment? something like

>

with lock:
   old = atomic_int
   atomic_int += 1

>

but in one operation

>
As above - the lock (under the assumption that it is actually a
threading.Lock) will ensure that.
>
Diez

Just out of interest, would the following, without a lock, be safe?

old, atomic_int = atomic_int, atomic_int+1

Frank Millman

[Paul Rubin]

Re: atomic increment

Frank Millman <frank@chagford .comwrites:

Just out of interest, would the following, without a lock, be safe?
old, atomic_int = atomic_int, atomic_int+1

No I don't think so. But I'm told that in CPython, you can say

counter = iter(xrange(100 00000)) # some number that exceeds what you'll use
...

atomic_int = counter.next()

and the GIL keeps it safe. When in doubt, use a lock or communicate
with other threads through Queues.

[Fredrik Lundh]

Re: atomic increment

Frank Millman wrote:

Just out of interest, would the following, without a lock, be safe?
>
old, atomic_int = atomic_int, atomic_int+1

nope.

there's some information here (make sure you read the comments):

http://effbot.org/pyfaq/what-kinds-of-global-value-mutation-are-thread-safe.htm

and some additional discussion here:

http://mail.python.org/pipermail/python-dev/2006-November/thread.html#69981

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