DKIM-Filter:	OpenDKIM Filter v2.11.0 delorie.com 46QLPIwn543930
Authentication-Results:	delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=xAyTfD2F
X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 9C1783860740
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1722029116;
	bh=bJPKkS5IvM1epqk04SXo9qK2Exu+5SsH5Da0Mq4cH7Q=;
	h=References:In-Reply-To:Date:Subject:To:List-Id:List-Unsubscribe:
	List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:
	From;
	b=xAyTfD2Ftv1LvJCjg2eqAKE3tNDhtEpQWr490+uVsYMKLjh95rtaZel56BNiBJXGB
	iGmI3Ycn67NQaLHubVQZBREtiLNyZ/PuvddBZ5uIJmxyr98F2NcFGbs4Gwa3Kz/YFo
	55qv8N/0XexvZvVDBuzmNXo1+yK0io1wMH4ClD9M=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
DMARC-Filter:	OpenDMARC Filter v1.4.2 sourceware.org 037993858C66
ARC-Filter:	OpenARC Filter v1.0.0 sourceware.org 037993858C66
ARC-Seal:	i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1722029061; cv=none;
	b=B0dMZKdVVnrLOJiQezTZO3o/ZQZN4nqVCYcT9pNAKIqzfMw2xcPCgBscmbIBtcDt6MMNONugtJonNPWZ+ZkxodZzjYhbpqmiooRRHeN33UZI/aKiW1uWq+q0Qi1Y5DSw2CsEa9tEt+64QZGNgjlGEUy20UtV9dCSwWWSKO9HuuE=
ARC-Message-Signature:	i=1; a=rsa-sha256; d=sourceware.org; s=key;
	t=1722029061; c=relaxed/simple;
	bh=IBjVUteWHAHNhwOuAVR/kGlzX8BOBNb12XjL9aL858k=;
	h=DKIM-Signature:MIME-Version:From:Date:Message-ID:Subject:To;
	b=tIn7PMqnFPbzFXUrlsJffytqVjrPuMB5zoytKELXAkCHogLKg3FAaWKEFBkheO7A03X9SrLCgkbfYFMw0P/WdAXGMlWwNab98ZwHZsSW7zRydpmKcfOwhd4p73Kjs332V8uNY1tEbccAc6rGVmt9hKV7JZafGhCjQYPjDzcxKqk=
ARC-Authentication-Results:	i=1; server2.sourceware.org
X-Google-DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=1e100.net; s=20230601; t=1722029057; x=1722633857;
	h=to:subject:message-id:date:from:in-reply-to:references:mime-version
	:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to;
	bh=IBjVUteWHAHNhwOuAVR/kGlzX8BOBNb12XjL9aL858k=;
	b=wp1kSE6t5hIRtU2d8rB9nGzJ1n7rc392ASAoqDaxvFcDJgu+xYilckFmaINnqurfT8
	JgAYU7WHNtIzhgcdoiUVwYul3cu2q8VyFtZC/Et78v0t2aSgC3LyfsmVjhrcHQS7pDgP
	kHApwuaUKPcV4fKO26+25Hi7WnMG8onLyhx2MVDJ6c37COU9ngvNGXnmRZXSO3VWXy9G
	s0PhtW87DiucDDjUpvSK+g5CNfL9Om/zYWSUL9iHo7PQLTQoI+uuZHFJY0v/tFck7tmX
	WEL6kSOML3BuN4Xmx5pFGKrsBoTVQr18GQiMbksw5SM4hk1S7ivo5vSBgyfzBO2teh9H
	kHXw==
X-Gm-Message-State:	AOJu0YxRtq//FN3Bu7/OKkShhbH6DBJimkx4rtJl3Xqw74xs289s1hqB
	eWAFa8Tx35UYXmHvQBNw9D19Servspm1zt0sKFfTG08GopTLK/25NihrsmjUIZwif1Bcq34h4/M
	NbToSEdcOiQsw2N5RB8lyilzYxZ95JA==
X-Google-Smtp-Source:	AGHT+IF5+Bgv0ZVhp8IQgJkBo+wR2q80iD91YF3mJtchyGLfuWZsY0zQE3Ij19/8EtcV+2swLIx8UJwUZvrJRT8cVno=
X-Received:	by 2002:a05:6a20:8403:b0:1c4:2132:e205 with SMTP id
	adf61e73a8af0-1c4a14df556mr774026637.48.1722029057168; Fri, 26 Jul 2024
	14:24:17 -0700 (PDT)
MIME-Version:	1.0
References:	<CADnnjUU5Q=C6S_8F9Akp3J5-t89O3i7xLoEsWqgXNRBPBkkdcw AT mail DOT gmail DOT com>
In-Reply-To:	<CADnnjUU5Q=C6S_8F9Akp3J5-t89O3i7xLoEsWqgXNRBPBkkdcw@mail.gmail.com>
Date:	Fri, 26 Jul 2024 17:24:01 -0400
Message-ID:	<CADnnjUUq+_sosM8yrc4a61F=nohqbC+PE=J9_o7TF7U-dVBNjw@mail.gmail.com>
Subject:	Re: Rewriting the FIFO code
To:	cygwin AT cygwin DOT com
X-Spam-Status:	No, score=-1.9 required=5.0 tests=BAYES_00, DKIM_SIGNED,
	DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, HTML_MESSAGE,
	RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS,
	TXREP autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version:	SpamAssassin 3.4.6 (2021-04-09) on
	server2.sourceware.org
X-Content-Filtered-By:	Mailman/MimeDel 2.1.30
X-BeenThere:	cygwin AT cygwin DOT com
X-Mailman-Version:	2.1.30
List-Id:	General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Archive:	<https://cygwin.com/pipermail/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe:	<https://cygwin.com/mailman/listinfo/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From:	Jameson Nash via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Jameson Nash <vtjnash AT gmail DOT com>
Sender:	"Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

I am hopping in late to this conversation, after working on debugging a
confusing issue where my NamedPipe stopped working reliably after being
passed to a cygwin program, where I believe it used to work okay with older
versions of cygwin. I just want to point out that the current flag being
used (Win32 calls it PIPE_NOWAIT) is documented as do-not-use (e.g.
https://devblogs.microsoft.com/oldnewthing/20110114-00/?p=11753) as it
interferes with the reliable execution of other programs that are using the
same pipe end, and that do not want to use the inefficient busy-wait
polling that cygwin's implementation does. As the documentation points out,
there is no way to recover correct behavior of OVERLAPPED while the flag is
enabled. By contrast, however, with PIPE_WAIT mode, it is possible to
implement non-blocking IO, including select, with OVERLAPPED operations, by
using ReadFile (with a size of 0) followed by PeekNamedPipe (if you want to
estimate the number of bytes to read) followed by a ReadFile of that number
of bytes (or an estimated number) followed by an immediate CancelIOEx (or
CancelIO on older platforms). I can post some example code from libuv if
that would be helpful? Removing this `PIPE_WAIT` change would eventually
also allow fixing the implementation of `select` in cygwin to actually use
event-driven notifications for readable instead of emulating it with a slow
poll loop as is done now (https://cygwin.com/cygwin-ug-net/highlights.html).

Thanks!

-jameson

post note: I also wrote up some of this in
https://github.com/libuv/libuv/issues/4467 so that google hopefully indexes
it in case anyone manages to run across the same problem in nodejs and
searches for related issues, but I only wrote a few details there of how
libuv might be impacted by this, without the specifics of how cygwin could
be fixed

second post note: sorry if this is a duplicate email, but I tried to send
it yesterday and forgot to enable plain text mode so it was first sent as
html and didn't seem to have gotten through to the list

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple

- Raw text -