From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.1 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham autolearn_force=no version=3.4.4 Received: from second.openwall.net (second.openwall.net [193.110.157.125]) by inbox.vuxu.org (Postfix) with SMTP id 7465322106 for ; Sat, 18 Jan 2025 12:31:25 +0100 (CET) Received: (qmail 19606 invoked by uid 550); 18 Jan 2025 11:31:22 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com x-ms-reactions: disallow Received: (qmail 19574 invoked from network); 18 Jan 2025 11:31:21 -0000 Date: Sat, 18 Jan 2025 06:31:12 -0500 From: Rich Felker To: Florian Weimer Cc: musl@lists.openwall.com Message-ID: <20250118113112.GN10433@brightrain.aerifal.cx> References: <87ed10mojw.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ed10mojw.fsf@mid.deneb.enyo.de> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] Linked stream handling On Sat, Jan 18, 2025 at 10:58:11AM +0100, Florian Weimer wrote: > Some of us interpret POSIX that it requires or at least encourages a > concept of linked streams: reading on from some streams may implicitly > flush certain other streams. (The language in the standard around > that is not particularly clear.) Linked streams may introduce > deadlocks (particularly with explicit locking if flockfile), so POSIX > suggests that implementations provide some form of deadlock detection, > failing certain stream operations. > > Do I read the sources correctly, and musl does not implement any of > this? musl very intentionally does not do any implicit flushing, because (1) it necessarily incurs deadlocks, and (2) it's useless because portable programs can't depend on it anyway but need to explicitly flush what they want, and musl generally favors making programs do the portable thing when there's no strong reason not to. I think the recommendation in POSIX to detect deadlocks is misguided because any deadlock beyond some trivial same-thread stuff that's unlikely to be the situation at hand is halting-equivalent to detect. The POSIX recommendation should be to drop the whole misguided legacy practice of auto-flushing that was invented in a single-threaded world on C implementations that could only open a small single- or double-digit number of FILEs at a time. Rich