Date: Wed, 4 Feb 2004 21:53:30 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Robert Watson <rwatson@freebsd.org> Cc: current@freebsd.org Subject: Re: Coalescing pipe allocation Message-ID: <20040204214426.U1469@gamplex.bde.org> In-Reply-To: <Pine.NEB.3.96L.1040203115210.79056E-100000@fledge.watson.org> References: <Pine.NEB.3.96L.1040203115210.79056E-100000@fledge.watson.org>
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On Tue, 3 Feb 2004, Robert Watson wrote: > On Tue, 3 Feb 2004, Peter Edwards wrote: > > > I have certainly taken that at face value at least once when deciding on > > how to use (or not use) pipes. Is this portability issue so > > ridiculously out of date that the comment in the pipe(2) manpage should > > be removed, or at least toned down? It seems silly to incur the costs of > > implementation you've mentioned and then recommend that the feature not > > be used. > Well, I don't know so much about the portability issues, but I can say > that it seems silly to incur the costs if few applications take advantage > of the feature. Especially if the cost can be defered until the feature Pipes were originally made bidirectional partly because this feature was "free": % RCS file: /home/ncvs/src/sys/kern/uipc_syscalls.c,v % Working file: uipc_syscalls.c % head: 1.171 % ... % ---------------------------- % revision 1.11 % date: 1996/01/01 10:28:21; author: peter; state: Exp; lines: +3 -3 % Make pipe() return a set of bidirectional pipe fd's rather than one-way only % just like on SVR4. % % This has no effect on any current programs in our source, but makes % the use of SVR4 code a little easier. There is no code or implementation % cost in the kernel.. This two-line change merely sets the modes on the ends % of the pipes to be bidirectional. There are no other changes. % ---------------------------- This was before optimization made the implementation of pipes complicated. Bruce
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