Usenet 1994 January/usenetsourcesnewsgroupsinfomagicjanuary1994.iso/sources/std_unix/reports/posix.4

Text File | 1991-09-06 | 5.4 KB | 203 lines

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.ds Rh POSIX.4, POSIX.4a, POSIX.4b, POSIX.13: Realtime POSIX
.ds Au Bill O. Gallmeister <[e-mail]>
.ds Dt July 8-12, 1991
.ds Lo Santa Clara, CA
.ds Ed Stephen R. Walli <[e-mail]>
.ds Wd U\s-3SENIX\s0 Standards Watchdog Committee
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.AF "\*(Ed, Report Editor"
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.P
\fB\*(Au\fP reports on \*(Su
.P
.HU "Summary"
.P
The working group continued work on Application
Profiles,
on the extended \s-1POSIX.4b\s0 Realtime Proposals,
and on the
thorny issues of \s-1IPC\s0 and synchronization mechanisms.
Since both
\s-1POSIX.4\s0
and
\s-1POSIX.4a\s0 are preparing for another ballot
recirculation,
there was little work done
on these drafts.
.P
.HU "Real-time Application Profiles"
.P
\s-1POSIX.4\s0 has produced four
different profiles,
matching different scales of real-time
endeavor.
The Embedded profile is meant for small machines that
may lack hardware for paging,
disks,
and terminals.
As such,
this
profile is rather different than what is generally considered
to be a
\s-1UNIX\(rg\s0
system.
In particular,
the threads work is called out,
and some of the \s-1POSIX.1\s0 file system,
but \fIfork()\fP
is not needed.
.P
This requires subsets of
\s-1POSIX.1\s0.
Its multiprocess
aspects
and
a lot of the extended filesystem
semantics are considered optional by the people working on the
smaller Real-Time profiles.
This subsetting work has to be
sanctioned by \s-1POSIX.1\s0.
Getting them to agree to this work
may be an interesting task.
.P
Other profiles under development are a
``Controller'' profile,
an ``Avionics'' profile,
and the ``Kitchen
Sink'' profile.
The Kitchen Sink
and
the Embedded profiles
define two endpoints of a spectrum of real-time practice.
The
Controller
and
Avionics profiles define particular points of practice within
that spectrum.
The Avionics profile reflects the current
requirements of the Avionics industry.
The Controller profile is
a step up from the Embedded profile.
.P
.HU "\s-1IPC\s0 Again"
.P
\s-1POSIX.4\s0 inter-process communication (\s-1IPC\s0) remains an issue.
We had a liaison meeting with the
\s-1POSIX.12\s0 (Protocol Independent Interfaces) working group
and
presented our requirements for a Real-Time sockets
mechanism.
There were 28 possible requirements;
we
decided that 17 of these requirements were truly necessary for
a socket-based mechanism for Real-Time \s-1IPC\s0.
The \s-1POSIX.12\s0 group
helped us refine these requirements into
something they can use in defining a mechanism.
These discussions
will undoubtedly carry on for some time.
.P
Meanwhile,
the existing \s-1POSIX.4\s0 \s-1IPC\s0 chapter is undergoing
radical surgery.
The recirculation draft that should come out this October
should feature an \s-1IPC\s0 mechanism that more closely
resembles the message passing interfaces of small real-time
kernels.
The interaction of this message-passing mechanism
and
the
future \s-1POSIX.12\s0 real-time sockets mechanism is an open issue.
.P
.HU "Synchronization Again"
.P
At the last meeting,
it was the \s-1POSIX.4\s0 proposal that needed
guidance from the working group on its binary semaphores chapter.
This meeting,
the \s-1POSIX.4a\s0 proposal required guidance with regards
to mutexes.
(Mutexes are simple \s-1MUT\s0ually \s-1EX\s0clusive locks.)
Specifically,
the priority ceiling protocols in
the current draft ran into serious balloting problems.
In
response to this,
a simplified version of the priority
ceiling protocol,
called Priority Ceiling Protocol Emulation,
was
proposed to replace the existing two mechanisms currently in
\s-1POSIX.4a\s0.
The emulation protocol is much easier to understand,
offers the same worst-case blocking behavior as the earlier
proposals
(although worse average-case behavior),
and works with
multiprocessor systems.
The working group was torn
whether
any priority ceiling protocol should be in \s-1POSIX.4a\s0 at all.
Assuming that one would be present,
the group clearly
preferred the emulation protocol.
.P
The debates on priority ceiling
featured a lively exchange between \s-1POSIX.4\s0
and
\s-1POSIX.14\s0 (Multiprocessor Profile).
This is the closest that \s-1POSIX.4\s0 has
come to its old glory days of large bloody group battles.
.P
.HU "\s-1POSIX.4b\s0"
.P
Some work was done on the timeout extensions of \s-1POSIX.4b\s0.
This work involves providing timeouts to all \s-1POSIX.4\s0 calls that may
block.
An early draft of this proposal is available in the latest
\s-1POSIX.4\s0 mailing.
.P
.HU "Future Drafts"
.P
The technical reviewers for \s-1POSIX.4\s0
and
\s-1POSIX.4a\s0 have been
working hard towards new drafts of each of these documents.
It is
our current plan to recirculate them both
at about
the same time as the Fall meeting.
If this happens,
the next meeting will again focus on application profiles and
continuing \s-1POSIX.4b\s0.