From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: some accept-process-output races fixed; Tramp FIXMEs Date: Wed, 16 Jan 2019 10:39:45 -0800 Organization: UCLA Computer Science Department Message-ID: <80d86b5a-efb7-87cc-a3db-0a6ad356274d@cs.ucla.edu> References: <46ce72ef-c4cb-1cd1-566a-c305ca92e68c@cs.ucla.edu> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------6CE3DFE841666D76F1D24BC9" X-Trace: blaine.gmane.org 1547664698 3282 195.159.176.226 (16 Jan 2019 18:51:38 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 16 Jan 2019 18:51:38 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 Cc: Michael Albinus , emacs-devel@gnu.org To: Stefan Monnier Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Wed Jan 16 19:51:34 2019 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gjqHl-0000iH-0l for ged-emacs-devel@m.gmane.org; Wed, 16 Jan 2019 19:51:33 +0100 Original-Received: from localhost ([127.0.0.1]:48792 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gjqJr-0008RO-9y for ged-emacs-devel@m.gmane.org; Wed, 16 Jan 2019 13:53:43 -0500 Original-Received: from eggs.gnu.org ([209.51.188.92]:37161) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gjqIM-0008C4-FY for emacs-devel@gnu.org; Wed, 16 Jan 2019 13:52:12 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gjq8b-000777-3n for emacs-devel@gnu.org; Wed, 16 Jan 2019 13:42:06 -0500 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:52484) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gjq8a-0005OL-Ih for emacs-devel@gnu.org; Wed, 16 Jan 2019 13:42:04 -0500 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 3638D160FEB; Wed, 16 Jan 2019 10:39:47 -0800 (PST) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id 54lezMjVWOh2; Wed, 16 Jan 2019 10:39:46 -0800 (PST) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 5576E161044; Wed, 16 Jan 2019 10:39:46 -0800 (PST) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id K68u-WXGnh_g; Wed, 16 Jan 2019 10:39:46 -0800 (PST) Original-Received: from Penguin.CS.UCLA.EDU (Penguin.CS.UCLA.EDU [131.179.64.200]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 37B43160F96; Wed, 16 Jan 2019 10:39:46 -0800 (PST) Openpgp: preference=signencrypt Autocrypt: addr=eggert@cs.ucla.edu; prefer-encrypt=mutual; keydata= xsFNBEyAcmQBEADAAyH2xoTu7ppG5D3a8FMZEon74dCvc4+q1XA2J2tBy2pwaTqfhpxxdGA9 Jj50UJ3PD4bSUEgN8tLZ0san47l5XTAFLi2456ciSl5m8sKaHlGdt9XmAAtmXqeZVIYX/UFS 96fDzf4xhEmm/y7LbYEPQdUdxu47xA5KhTYp5bltF3WYDz1Ygd7gx07Auwp7iw7eNvnoDTAl KAl8KYDZzbDNCQGEbpY3efZIvPdeI+FWQN4W+kghy+P6au6PrIIhYraeua7XDdb2LS1en3Ss mE3QjqfRqI/A2ue8JMwsvXe/WK38Ezs6x74iTaqI3AFH6ilAhDqpMnd/msSESNFt76DiO1ZK QMr9amVPknjfPmJISqdhgB1DlEdw34sROf6V8mZw0xfqT6PKE46LcFefzs0kbg4GORf8vjG2 Sf1tk5eU8MBiyN/bZ03bKNjNYMpODDQQwuP84kYLkX2wBxxMAhBxwbDVZudzxDZJ1C2VXujC OJVxq2kljBM9ETYuUGqd75AW2LXrLw6+MuIsHFAYAgRr7+KcwDgBAfwhPBYX34nSSiHlmLC+ KaHLeCLF5ZI2vKm3HEeCTtlOg7xZEONgwzL+fdKo+D6SoC8RRxJKs8a3sVfI4t6CnrQzvJbB n6gxdgCu5i29J1QCYrCYvql2UyFPAK+do99/1jOXT4m2836j1wARAQABzSBQYXVsIEVnZ2Vy dCA8ZWdnZXJ0QGNzLnVjbGEuZWR1PsLBfgQTAQIAKAUCTIByZAIbAwUJEswDAAYLCQgHAwIG FQgCCQoLBBYCAwECH In-Reply-To: Content-Language: en-US X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 131.179.128.68 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:232401 Archived-At: This is a multi-part message in MIME format. --------------6CE3DFE841666D76F1D24BC9 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 1/16/19 5:25 AM, Stefan Monnier wrote: > So how can the code tell when it has read all the data? The code keeps calling accept-process-output until it gets nil. Now that I think about it, if you just want all the data you needn=E2=80=99= t=20 call process-live-p. I installed the attached doc patch accordingly. The Tramp code still contains several loops like this: =C2=A0 (while (or (accept-process-output p 0.1) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= (process-live-p p))) that suffer from race conditions. Consider the following sequence of even= ts: * accept-process-output times out after 0.1 seconds, and returns nil. * P generates some data and then exits. * process-live-p returns nil. In this case the loop will exit and lose data. This bug is caused by the=20 " 0.1" in that loop. I don=E2=80=99t know why the " 0.1" is there, but if= the "=20 0.1" has to be there then I suppose one way to fix the bug would be to=20 enhance accept-process-output so that its caller can distinguish a=20 timeout from a connection-closed. --------------6CE3DFE841666D76F1D24BC9 Content-Type: text/x-patch; name="0001-doc-lispref-processes.texi-Accepting-Output-Simplify.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename*0="0001-doc-lispref-processes.texi-Accepting-Output-Simplify.pa"; filename*1="tch" >From b76e90d242e9ee0a733fc9d4b6e280eb6892a6d0 Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Wed, 16 Jan 2019 10:31:21 -0800 Subject: [PATCH] * doc/lispref/processes.texi (Accepting Output): Simplify. --- doc/lispref/processes.texi | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/doc/lispref/processes.texi b/doc/lispref/processes.texi index afda8aede8..fd6686e882 100644 --- a/doc/lispref/processes.texi +++ b/doc/lispref/processes.texi @@ -1870,13 +1870,13 @@ Accepting Output @end example @noindent -will often work, it has a race condition and can miss some output if -@code{process-live-p} returns @code{nil} while the connection still -contains data. Better is to write the loop like this: +will often read all output from @var{process}, it has a race condition +and can miss some output if @code{process-live-p} returns @code{nil} +while the connection still contains data. Better is to write the loop +like this: @example -(while (or (accept-process-output process) - (process-live-p process))) +(while (accept-process-output process)) @end example @node Processes and Threads -- 2.20.1 --------------6CE3DFE841666D76F1D24BC9--