From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/13845 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: fgets() doesn't call fsync() before getting input Date: Thu, 21 Feb 2019 15:44:19 -0500 Message-ID: <20190221204419.GJ23599@brightrain.aerifal.cx> References: <20190221152243.GF23599@brightrain.aerifal.cx> <5c1de98e-9606-81d6-0e69-8f3dbb916065@adelielinux.org> <20190221170748.GI23599@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="155581"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mutt/1.5.21 (2010-09-15) To: musl@lists.openwall.com Original-X-From: musl-return-13861-gllmg-musl=m.gmane.org@lists.openwall.com Thu Feb 21 21:44:35 2019 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.89) (envelope-from ) id 1gwvCs-000eKX-2J for gllmg-musl@m.gmane.org; Thu, 21 Feb 2019 21:44:34 +0100 Original-Received: (qmail 26494 invoked by uid 550); 21 Feb 2019 20:44:31 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 26476 invoked from network); 21 Feb 2019 20:44:31 -0000 Content-Disposition: inline In-Reply-To: Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:13845 Archived-At: On Thu, Feb 21, 2019 at 03:16:23PM -0500, James Larrowe wrote: > Sorry, this was a typo. I meant fflush(). However, it's still not called. > It's fixed in my program now, however I'm not sure what to do in this case. > Do I just call ffush() on stdin, stdout, and stderr or do I send a patch to > fgets()? If you want to ensure the output to stdout actually appears on the terminal/output file before some point in your program, you need to call fflush(stdout) at that point. In your case that would be between the fputs and fgets calls. Rich > On Thu, Feb 21, 2019 at 12:08 PM Rich Felker wrote: > > > On Thu, Feb 21, 2019 at 10:31:36AM -0600, A. Wilcox wrote: > > > On 02/21/19 09:22, Rich Felker wrote: > > > > On Thu, Feb 21, 2019 at 10:09:03AM -0500, James Larrowe wrote: > > > >> I'm writing a program that prints a dialogue to the screen and then > > asks > > > >> for input. In musl, the dialogue does not show before fgets() is > > called, > > > >> however in glibc it does. That causes a blank prompt and also some > > > >> confusion. Attached is a minimal example and a log. > > > > > > > > This difference is intentional. The specification allows but does not > > > > require that attempting to read from a line-buffered input stream > > > > causes all line-buffered output streams to be flushed. This behavior > > > > was somewhat convenient for old-style input-prompt idioms, but it > > > > doesn't scale with large numbers of files open and deadlocks with some > > > > multi-threaded usage. The portable solution here for applications is > > > > to fflush (not fsync) the particular stream you want flushed. > > > > > > > > Rich > > > > > > > > > FWIW, the only package we've come across where this is a problem is > > > mac-fdisk (which hasn't been updated since 1997 - yes, 22 years ago). > > > > > > We have a patch: > > > > > > > > https://code.foxkit.us/adelie/packages/blob/master/user/mac-fdisk/flush-stdout.patch > > > > I think it's more of an issue for the early examples in C books and > > tutorials, which invariably but inexplicably use a 1970s-era "prompt > > for input" model rather than argv[] or something that would be a lot > > more familiar (and amenable to testing) to modern readers. > > > > Rich > >