From: Clem Cole <clemc@ccc.com>
To: Paul Ruizendaal <pnr@planet.nl>
Cc: TUHS main list <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] non-blocking IO
Date: Sun, 31 May 2020 12:05:47 -0400 [thread overview]
Message-ID: <CAC20D2McV_i0d=m33McRVoPda8ZVLawaKJxndYDLbqAnHLE_Wg@mail.gmail.com> (raw)
In-Reply-To: <ADC32296-73FD-46D4-A3D6-4EA03A956103@planet.nl>
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On Sun, May 31, 2020 at 7:10 AM Paul Ruizendaal <pnr@planet.nl> wrote:
> This behaviour seems to have continued into SysVR1, I’m not sure when
> EAGAIN came into use as a return value for this use case in the SysV
> lineage. Maybe with SysVR3 networking?
Actually, I'm pretty sure that was a product of the POSIX discussions. BSD
already had networking an EWOULDBLOCK. We had argued about EWOULDBLOCK a
great deal, we also were arguing about signal semantics. I've forgotten
many of the details, Heinz may remember more than I do. EAGAIN was created
as a compromise -- IIRC neither system had it yet. SVR3 networking was
where it went into System V, although some of the AT&T representatives were
none too happy about it.
>
> In the Research lineage, the above SysIII approach does not seem to exist,
> although the V8 manual page for open() says under BUGS "It should be
> possible [...] to optionally call open without the possibility of hanging
> waiting for carrier on communication lines.” In the same location for V10
> it reads "It should be possible to call open without waiting for carrier on
> communication lines.”
>
> The July 1981 design proposals for 4.2BSD note that SysIII non-blocking
> files are a useful feature and should be included in the new system. In
> Jan/Feb 1982 this appears to be coded up, although not all affected files
> are under SCCS tracking at that point in time. Non-blocking behaviour is
> changed from the SysIII semantics, in that EWOULDBLOCK is returned instead
> of 0 when progress is not possible. The non-blocking behaviour is extended
> beyond TTY’s and pipes to sockets, with additional errors (such as
> EINPROGRESS). At this time EWOULDBLOCK is not the same error number as
> EGAIN.
>
My memory is that Keith was the BSD (CSRG) person at the POSIX meeting (he,
Jim McGinness of DEC, and I created PAX at one point as a compromise). I
wish I could remember all of the details, but this was all argued at the
POSIX meetings.
As I said before the folks from AT&T just wanted to take the SVID and
rubber stamp it at the specification. Part of it the problem was they
wanted to be free to do what things/make choices that the rest of us might
or might not like (for instance, they did not want the sockets interface).
>
> It would seem that the differences between the BSD and SysV lineages in
> this area persisted until around 2000 or so.
>
Yep - cause around then POSIX started to settle out and both systems began
to follow it.
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next prev parent reply other threads:[~2020-05-31 16:06 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-31 11:09 Paul Ruizendaal
2020-05-31 16:05 ` Clem Cole [this message]
2020-05-31 16:46 ` Warner Losh
2020-05-31 22:01 ` Rob Pike
2020-06-01 3:32 ` Dave Horsfall
2020-06-01 14:58 ` Larry McVoy
2020-06-04 9:04 ` Peter Jeremy
2020-06-04 14:19 ` Warner Losh
2020-06-04 16:34 ` Tony Finch
2020-06-04 16:50 ` Larry McVoy
2020-06-05 16:00 ` Dan Cross
2020-06-12 8:18 ` Dave Horsfall
2020-06-01 16:58 ` Heinz Lycklama
2020-06-01 23:17 Noel Chiappa
2020-06-02 0:08 Noel Chiappa
2020-06-02 8:22 Paul Ruizendaal
2020-06-02 14:19 Paul Ruizendaal
2020-06-02 17:45 ` Paul Winalski
2020-06-02 17:59 ` arnold
2020-06-02 18:53 ` Paul Winalski
2020-06-02 19:18 ` Clem Cole
2020-06-02 21:15 ` Lawrence Stewart
2020-06-02 18:23 ` Dan Cross
2020-06-02 18:56 ` Paul Winalski
2020-06-02 19:23 ` Clem Cole
2020-06-02 20:13 Noel Chiappa
2020-06-02 20:43 ` Clem Cole
2020-06-02 22:14 ` Rich Morin
2020-06-03 16:31 ` Paul Winalski
2020-06-03 19:19 ` John P. Linderman
2020-06-06 13:29 Noel Chiappa
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