Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.xs4all.nl!newsfeed3.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <rosuav@gmail.com>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.051
X-Spam-Evidence: '*H*': 0.90; '*S*': 0.00; '(even': 0.05; 'advocate': 0.07; 'subject:script': 0.09; 'python': 0.11; 'corrupt': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'mutated': 0.16; 'objects.': 0.16; 'roy': 0.16; 'subject:versus': 0.16; 'wrote:': 0.18; 'meant': 0.20; 'appears': 0.22; 'certainly': 0.24; 'lets': 0.24; "shouldn't": 0.24; 'sorry,': 0.24; 'right.': 0.26; 'header:In-Reply-To:1': 0.27; 'am,': 0.29; 'generally': 0.29; 'message-id:@mail.gmail.com': 0.30; "i'm": 0.30; 'code': 0.31; 'easier': 0.31; 'occurs': 0.31; 'purely': 0.31; 'anyone': 0.31; 'file': 0.32; 'running': 0.33; 'fri,': 0.33; "i'd": 0.34; 'but': 0.35; 'received:google.com': 0.35; 'really': 0.36; 'doing': 0.36; 'possible': 0.36; 'example,': 0.37; 'two': 0.37; 'level': 0.37; 'awesome': 0.38; 'needed': 0.38; 'to:addr:python-list': 0.38; 'anything': 0.39; 'though,': 0.39; 'to:addr:python.org': 0.39; 'lower': 0.61; 'range': 0.61; 'simple': 0.61; "you're": 0.61; 'kind': 0.63; 'soon': 0.63; 'different': 0.65; 'smith': 0.68; 'guaranteed': 0.75; 'protects': 0.84; 'eliminates': 0.91; 'political': 0.97; '2013': 0.98
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=XaOQbSRgWb8t8ehLqR3hctU5LseC1rQE9C5p+KdrUag=; b=XgInbgeHH3hhGxKnR9UVovozar+QxAwGr69g3d2pxwH/LzWTirAGcNPEz3GHMsk+5H jxHCMHsq5AUcfbi2f+quBcEQM1+d98pK0qYca6r1wlU7gZS/kfekHPqFx7z3X5nIfJbR oAFZlb7/AltvXev/+BRmnBzeYgmQVihBRQE1PDldbu84SpDR7wtjQPe8r04fJSGlEZ8W 7Cx8dJOQA0mbuEOhA4Y2HrfOuIMxtDkLStUF880ZdarsqPrJV++1OlqponPdrrafyIJ3 8kvKdqdKApw1fYwroC6vBZDuX4b4lCpXuiYLyReP/w7QVrG/DUNmBE6W+XxoQUUPgQBQ qx5g==
MIME-Version: 1.0
X-Received: by 10.66.154.1 with SMTP id vk1mr11157908pab.85.1380825385953; Thu, 03 Oct 2013 11:36:25 -0700 (PDT)
In-Reply-To: <roy-D617DD.14283203102013@news.panix.com>
References: <f01b2e7a-9fc7-4138-bb6e-447d31179f2d@googlegroups.com> <roy-451497.12415103102013@news.panix.com> <mailman.684.1380819470.18130.python-list@python.org> <roy-D617DD.14283203102013@news.panix.com>
Date: Fri, 4 Oct 2013 04:36:25 +1000
Subject: Re: Multiple scripts versus single multi-threaded script
From: Chris Angelico <rosuav@gmail.com>
To: python-list@python.org
Content-Type: text/plain; charset=ISO-8859-1
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <http://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups: comp.lang.python
Message-ID: <mailman.691.1380825390.18130.python-list@python.org>
Lines: 24
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1380825390 news.xs4all.nl 15891 [2001:888:2000:d::a6]:41606
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:55437

On Fri, Oct 4, 2013 at 4:28 AM, Roy Smith <roy@panix.com> wrote:
> Well, the GIL certainly eliminates a whole range of problems, but it's
> still possible to write code that deadlocks.  All that's really needed
> is for two threads to try to acquire the same two resources, in
> different orders.  I'm running the following code right now.  It appears
> to be doing a pretty good imitation of a deadlock.  Any similarity to
> current political events is purely intentional.

Right. Sorry, I meant that the GIL protects you from all that
happening in the lower level code (even lower than the Senate, here),
but yes, you can get deadlocks as soon as you acquire locks. That's
nothing to do with threading, you can have the same issues with
databases, file systems, or anything else that lets you lock
something. It's a LOT easier to deal with deadlocks or data corruption
that occurs in pure Python code than in C, since Python has awesome
introspection facilities... and you're guaranteed that corrupt data is
still valid Python objects.

As to your corrupt data example, though, I'd advocate a very simple
system of object ownership: as soon as the object has been put on the
queue, it's "owned" by the recipient and shouldn't be mutated by
anyone else. That kind of system generally isn't hard to maintain.

ChrisA