Path: csiph.com!news.swapon.de!fu-berlin.de!uni-berlin.de!not-for-mail From: "Frank Millman" Newsgroups: comp.lang.python Subject: Re: asyncio - how to stop background task cleanly Date: Sat, 6 Feb 2016 16:01:49 +0200 Lines: 52 Message-ID: References: <87lh6ys052.fsf@elektro.pacujo.net> Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Trace: news.uni-berlin.de lTcgqQF5/Wzs7jqFzR34awE9h81m0cap6XvrfpU0SZHA== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.014 X-Spam-Evidence: '*H*': 0.97; '*S*': 0.00; 'cleanup,': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'def': 0.13; 'async': 0.16; 'cleanly': 0.16; 'evt.set()': 0.16; 'hint': 0.16; 'received:80.91.229.3': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'subject:stop': 0.16; 'thread.': 0.16; 'threading,': 0.16; 'threads:': 0.16; 'wrote': 0.23; 'finished': 0.23; 'thanks,': 0.24; 'header:In-Reply-To:1': 0.24; 'header:X-Complaints-To:1': 0.26; 'appreciated.': 0.27; 'figure': 0.27; 'equivalent': 0.27; 'figured': 0.29; 'initiate': 0.29; 'loop,': 0.29; 'really,': 0.29; 'sleep': 0.29; 'task': 0.30; 'another': 0.32; 'possibly': 0.32; 'run': 0.33; 'problem': 0.33; 'true.': 0.33; 'gives': 0.35; 'could': 0.35; 'false': 0.35; 'i.e.': 0.35; 'stopped': 0.35; 'but': 0.36; 'should': 0.36; 'there': 0.36; '(and': 0.36; 'to:addr :python-list': 0.36; 'subject:: ': 0.37; 'setting': 0.37; 'thanks': 0.37; 'received:org': 0.37; 'someone': 0.38; 'skip:e 20': 0.39; 'well.': 0.40; 'to:addr:python.org': 0.40; 'where': 0.40; 'some': 0.40; 'here': 0.66; 'frank': 0.72; 'skip:n 40': 0.72; 'await': 0.76; 'stimuli.': 0.84; 'superiority': 0.84; 'working,': 0.84; 'instantly.': 0.91; 'task,': 0.91 X-Injected-Via-Gmane: http://gmane.org/ X-Gmane-NNTP-Posting-Host: 197.89.169.151 In-Reply-To: <87lh6ys052.fsf@elektro.pacujo.net> X-MSMail-Priority: Normal Importance: Normal X-Newsreader: Microsoft Windows Live Mail 15.4.3502.922 X-MimeOLE: Produced By Microsoft MimeOLE V15.4.3502.922 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.21rc2 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Xref: csiph.com comp.lang.python:102583 "Marko Rauhamaa" wrote in message news:87lh6ys052.fsf@elektro.pacujo.net... > > "Frank Millman" : > > > When shutting the main program down, I want to stop the task, but I > > cannot figure out how to stop it cleanly - i.e. wait until it has > > finished the current task and possibly performed some cleanup, before > > continuing. > > Here (and really, only here) is where asyncio shows its superiority over > threads: you can multiplex. > > You should > > await asyncio.wait(..., return_when=asyncio.FIRST_COMPLETED) > > to deal with multiple alternative stimuli. > Thanks, Marko, that works very well. It took me a while to get it working, because I initiate shutting down the program from another thread. Eventually I figured out that I could put all my event loop shutdown procedures into a coroutine, and then call asyncio.run_coroutine_threadsafe() from the main thread. Now I just have one problem left. I will keep experimenting, but if someone gives me a hint in the meantime it will be appreciated. I run my background task like this - stop_task = False async def background_task(): while not stop_task: await perform_task() await asyncio.sleep(10) I stop the task by setting stop_task to True. It works, but it waits for the 10-second sleep to expire before it is actioned. With threading, I could set up a threading.Event(), call evt.wait(timeout=10) to run the loop, and evt.set() to stop it. It stopped instantly. Is there an equivalent in asyncio? Thanks Frank