Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail From: "Frank Millman" Newsgroups: comp.lang.python Subject: Re: Question about asyncio and blocking operations Date: Tue, 26 Jan 2016 16:15:30 +0200 Lines: 40 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Content-Transfer-Encoding: 7bit X-Trace: news.uni-berlin.de bUdfZ615qXux0z9aABWZywgBj37Sqr4n9xt5YmyNjRjA== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'ignored': 0.05; 'subject:Question': 0.05; 'caller': 0.07; 'front-end': 0.07; 'back-end': 0.09; 'cursor': 0.09; 'iterate': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'requested.': 0.09; 'rows': 0.09; 'tackle': 0.09; 'def': 0.13; 'operation.': 0.16; 'received:80.91.229.3': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'row': 0.16; 'stage.': 0.16; 'typical': 0.18; 'together.': 0.20; 'aspect': 0.22; 'bit': 0.23; 'seems': 0.23; 'wrote': 0.23; 'header :In-Reply-To:1': 0.24; 'header:X-Complaints-To:1': 0.26; 'yield': 0.27; 'developing': 0.28; 'another.': 0.29; 'blocking': 0.29; 'system,': 0.30; 'that.': 0.30; 'possibly': 0.32; 'run': 0.33; 'usually': 0.33; 'right?': 0.33; "isn't": 0.35; 'but': 0.36; 'should': 0.36; 'there': 0.36; 'to:addr:python-list': 0.36; 'subject:: ': 0.37; 'received:org': 0.37; 'list.': 0.37; 'does': 0.39; 'application': 0.39; 'to:addr:python.org': 0.40; 'some': 0.40; 'future': 0.60; 'clients': 0.61; 'making': 0.62; 'worth': 0.67; 'frank': 0.72; 'sound': 0.72; 'mention.': 0.84 X-Injected-Via-Gmane: http://gmane.org/ X-Gmane-NNTP-Posting-Host: 197.89.154.138 In-Reply-To: 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: 2.1.20+ 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:102121 "Frank Millman" wrote in message news:n8038j$575$1@ger.gmane.org... > > I am developing a typical accounting/business application which involves a > front-end allowing clients to access the system, a back-end connecting to > a database, and a middle layer that glues it all together. > [...] > > There was one aspect that I deliberately ignored at that stage. I did not > change the database access to an asyncio approach, so all reading > from/writing to the database involved a blocking operation. I am now ready > to tackle that. I am making some progress, but I have found a snag - possibly unavoidable, but worth a mention. Usually when I retrieve rows from a database I iterate over the cursor - def get_rows(sql, params): cur.execute(sql, params) for row in cur: yield row If I create a Future to run get_rows(), I have to 'return' the result so that the caller can access it by calling future.result(). If I return the cursor, I can iterate over it, but isn't this a blocking operation? As far as I know, the DB adaptor will only actually retrieve the row when requested. If I am right, I should call fetchall() while inside get_rows(), and return all the rows as a list. This seems to be swapping one bit of asynchronicity for another. Does this sound right? Frank