Time to write a signal handler?

Unix Creators at DEC PDP11
Unix Creators at DEC PDP11 (Photo credit: PanelSwitchman)

I am trying to execute some self-written pieces of software that require a lot of wall clock time – around three weeks.

I run them on the University of York‘s compute server which is rebooted on the first Tuesday of every month, so the window for the software is limited. I have until about 7 am on 5 August before the next reboot.

To add to the complication the server runs Kerberos which does not seem to play well with the screen/NFS combination I am using.

And – I keep killing the applications in error – this time, just half an hour ago I assume I was on a dead terminal session (ie an ssh login which had long since expired) and pressed ctrl-C, only to my horror to discover it was a live screen (it had not responded to ctrl-A, ctrl-A for whatever reason).

Time to add a signal handler to catch ctrl-C to at least give me the option of changing my mind!

Reasoning about a NoC

Thinking about a Network-on-Chip system and what its system software needs to do…

  • Parallelisation is essential to efficiency – in a NoC there are a multitude of cores, but each core has only the fraction of the computational power a “traditional” unicore might be expected to have – therefore it is essential that, where possible, code is parallelised across as many cores as possible;
  • Each core needs to be able to access operating system services (via system calls or some other mechanism), but it is not necessarily the case that each core has to run a full or even a partial operating system – thus RPC or some other mechanism can be used to ‘remotely’ provide system services;
  • Application programmers want, above all, a single address space.


Twenty years of Windows NT

Windows NT 3.1
Windows NT 3.1 (Photo credit: Wikipedia)

Today is the twentieth anniversary of the launch of Windows NT. In fact I have been using it (I still have to – in the sense that Windows XP/7/8 are NT – on occasion) for a bit longer than that as I was a member of the NT beta programme – I even managed to write some software for it using the 32 bit SDK before it was officially released (a not very good version of exie-ohsies/naughts-and-crosses/tic-tac-toe – so poor was the coding that you could beat the computer every time if you knew its weakness).

NT would not run on my Amstrad 386 and in the end I bought a cheap 486 machine to match the software – it was a lot of fun in the early days – though I shudder to think of trying to get by, day by day, on a machine with such a weak command line.

One thing I remember was the late, great, Byte magazine running an issue in the summer of 1992 predicting that NT would be the death of Unix. I even thought that was right – Unix was for expensive workstations and now us users of commodity hardware were to get a proper multi-tasking 32 bit operating system – who needed time-sharing when we could all have PCs of our own?

Computer science in the UK: in the wrong direction?

Servers designed for Linux
Servers designed for Linux (Photo credit: Wikipedia)

Two big thoughts strike me as a result of the literature review I have just completed for my PhD:

  • Linux is not the centre of the universe, in fact it is a bit of an intellectual backwater;
  • The UK may have played as big a role in the invention of the electronic computer as the US, but these days it is hardly even in the game in many areas of computing research.

On the first point I am in danger of sounding like Andy “Linux is obsolete” Tanenbaum – but it is certainly the case that Linux is far from the cutting edge in operating system research. If massively parallel systems do break through to the desktop it is difficult to imagine they will be running Linux (or any monolithic operating system).

In fact the first generation may do – because nobody has anything else right now – but Linux will be a kludge in that case.

Doing my MSc which did focus on a Linux related problem, it seemed to me that we had come close to “the end of history” in  operating system research – ie the issue now was fine tuning the models we had settled on. The big issues had been dealt with in the late 60s, the 70s and the 80s.

Now I know different. Operating systems research is very vibrant and there are lots of new models competing for attention.

But along the way the UK dropped out of the picture. Read some papers on the development of virtual memory and it will not be long before you come across the seminal experiment conducted on EMAS – the Edinburgh University Multiple Access System – which was still in use when I was there in 1984. Now you will struggle to find any UK university – with the limited exceptions of Cambridge and York (for real-time) – making any impact (at least that’s how it seems to me).

It’s not that the Americans run the show either – German, Swiss and Italian universities are leading centres of research into systems software.

I am not sure how or why the UK slipped behind, but it feels like a mistake to me – especially as I think new hardware models are going to drive a lot of software innovation in the next decade (well, I would say that, wouldn’t I?)

A Raspberry Pi project?

Unix filesystem
Unix filesystem (Photo credit: Wikipedia)

My Raspberry Pis are likely to be dispatched tomorrow.

Wondering if I should use the little Plan 9 installation I plan to build as a testbed for a parallel filesystem (that I write).

As preparation for next week’s literature review seminar I read about the Vesta filesystem and find it absolutely fascinating. Could we build a new filesystem – Pallas? – which combines the Vesta approach with support for Unix semantics?

Plan9 on the Raspberry Pi

Glenda, the Plan 9 Bunny
Glenda, the Plan 9 Bunny (Photo credit: Wikipedia)

Plan 9 from Bell Labs” was meant to be the successor system to Unix and like the original was designed and built by AT&Ts engineers at Bell Labs(the title is, of course, a skit on what is supposedly the best worst-ever film – “Plan 9 from Outer Space”).

Plan 9 never really made it. Linux came along and gave us Unix for the masses on cheap hardware for free and the world moved on. (Though some of the ideas in Plan 9 were retro-fitted into Linux and other Unix-like systems.)

The increased speed of commodity computers – latterly sustained via SMP – meant that computing power that once seemed only available to the elite could be found on the High Street and easy to use and install clustering software meant scientists and others could build super-computers using cheap hardware and free software. The multi-computer idea at the heart of Plan 9 seemed to have been passed-by as we screamed along the Moore’s Law Highway.

But now Moore’s Law is breaking down – or rather we are discovering that while the Law continues to apply – in other words we can still double the number of transistors on silicon every 18 – 24 months – other factors (heat dissipation essentially) mean we cannot translate a doubling of transistors into a computer that runs twice as fast. And so the multi-computer idea is of interest once more.

Plan 9 is not likely to be the operating system of the future. But as an actually existing multi-computer operating system it could still have a lot to teach us.

Now it has been ported to run on the Raspberry Pi single board computer I have decided to order another three of these things (I already have one running as a proxy server) and use them as Plan 9 nodes. The boards should be here in about three weeks (I hope), meaning I will have them as a Christmas present to myself.

OS/2: killed by Bill?

OS/2 logo
OS/2 logo (Photo credit: Wikipedia)

Here is a fascinating account of the rise and fall of OS/2, the operating system that was supposed to seal IBM’s (and Microsoft’s) global domination. Instead it flopped, being beaten by a poorer quality alternative in the form of Windows 3.0/3.1 after Microsoft pulled out.

I remember when Windows NT was launched in 1993 – one of its selling points was its ability to run OS/2 1.0 software natively via a dedicated subsystem (strange to remember, but then Microsoft went heavy on the modular nature of NT and its ability to run on non-Intel hardware and to support different software on top of the microkernel).

I could only ever find one free piece of native OS/2 software to run – a hex editor. A fundamentally vital workhorse for any programmer yet good implementations always seem to be in short supply (even now – last month I seriously considered writing my own so fed up was I with the basic offerings that come with Linux flavours). This one – its name escapes me – was a goodie though and I was a bit cheesed off when an NT upgrade (to 3.5) broke it. By then Microsoft plainly did not care much for software compatibility (or for NT’s ability to run on different platforms – that was scrapped too).

Still, OS/2 had its fans. As a journalist reporting on housing I went to see a public sector housing manager in rural Somerset at about this time: he was pioneering a new software system for his district housing offices and OS/2, with its revolutionary object-orientated desktop (which is what right clicking is all about) was to be at the core of that – with housing officers treating the desktop like various forms on which they could order repairs and so on. It was difficult not to share his enthusiasm because the idea, now a commonplace, that objects on the desktop could be more than just program icons was so new and exciting.

The article lists the ways in which Microsoft went all out to kill OS/2 and, in every practical sense, they succeeded. Those who doubt the need for free-as-in-freedom software should consider that. But it also lists various places where OS/2 is still in use (in the US). Anyone know of similar examples in the UK?