Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!selfless.tophat.at!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.013 X-Spam-Evidence: '*H*': 0.97; '*S*': 0.00; 'think,': 0.05; 'python': 0.08; 'answer?': 0.09; 'concurrency': 0.09; 'subject:problems': 0.09; 'subject:python': 0.12; 'wrote:': 0.15; 'invocations': 0.16; 'message-id:@web.de': 0.16; 'met,': 0.16; 'subject: \n ': 0.16; 't.start()': 0.16; 'thread.': 0.16; 'threading': 0.16; 'tries': 0.16; 'def': 0.16; 'issue,': 0.19; 'subject:not': 0.21; 'mechanism': 0.22; 'header:In-Reply-To:1': 0.22; 'problem?': 0.23; 'times,': 0.25; 'function': 0.26; 'import': 0.29; "skip:' 30": 0.29; 'variables': 0.29; 'from:addr:web.de': 0.30; 'subject:?': 0.31; 'shared': 0.32; 'print': 0.32; 'to:addr:python-list': 0.34; 'header:User-Agent:1': 0.34; 'there': 0.34; 'function.': 0.35; 'data,': 0.35; 'thread': 0.37; 'some': 0.37; 'but': 0.37; 'subject:: ': 0.38; 'two': 0.38; 'run': 0.39; 'case': 0.39; 'should': 0.39; "there's": 0.39; 'to:addr:python.org': 0.39; 'your': 0.60; 'total': 0.61; 'subject:program': 0.67; 'special': 0.67; 'received:172.20': 0.73; 'why?': 0.73; 'programming?': 0.84; 'sender:addr:web.de': 0.84; 'subject:any': 0.84; 'subject:face': 0.84 Date: Sat, 09 Jul 2011 23:17:29 +0200 From: Alexander Kapps User-Agent: Mozilla/5.0 (X11; U; Linux i686; de-DE; rv:1.9.2.17) Gecko/20110424 Thunderbird/3.1.10 MIME-Version: 1.0 To: python-list@python.org Subject: Re: why the following python program does not face any concurrency problems without synchronize mechanism? References: In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: alex.kapps@web.de X-Sender: Alex.Kapps@web.de X-Provags-ID: V01U2FsdGVkX18lX4bAdHCFyczeS48QZrH9QvZmCwQ9skNAcdHy 0ExRu8g5qpNJv+t4ufxl/AJuq0reWOql/nlP5QvuXLkYuLjdjC wZrBO9184= X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 30 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1310246258 news.xs4all.nl 21883 [2001:888:2000:d::a6]:54099 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:9116 On 09.07.2011 22:45, smith jack wrote: > from threading import Thread > > def calc(start, end): > total = 0; > for i in range(start, end + 1): > total += i; > print '----------------------result:', total > return total > > t = Thread(target=calc, args=(1,100)) > t.start() > > I have run this program for many times,and the result is always 5050, > if there is any concurrency problem, the result should not be 5050, > which is never met, anyhow > I mean this program should get the wrong answer at some times, but > this never happens, why? > can concurrency without synchronize mechanism always get the right answer? > any special case in python programming? Why do you think, that there's a concurrency problem? All variables are local to the calc() function and all calc() invocations run in an own thread. No thread tries to access any shared data, so why should there be a concurrency problem? Concurrency is an issue, when two or more threads/processes try to access the same data, but in your program everything is local to the calc() function.