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An immutable operating system

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Re: An immutable operating system

#21

Post by jrockway »

mhurron wrote: post #12
eloff wrote: post #6

An operating system whose main goal is not performance is forever going to be a toy of professors. Linux is a mess compared to the beautiful code that would comprise this OS, but it's a mess that runs fast on real hardware and let's people get stuff done. That matters.

Sometimes 'toy of professors' (research) is the point. Not everything has to run a social network and not everyone is working on a twitter clone.

Isn't Twitter written in Scala, a programming language designed with immutability in mind?

Re: An immutable operating system

#22

Post by brandonbloom »

Someone wrote: post #13
stcredzero wrote: post #7

A garbage collector that knows that all values are immutable will be rather interesting, I think. Typically, a garbage collector will stop the world (i.e. halt execution) to do heap defragmentation of the old generation. When all values are immutable, though, you can defragment the heap by copying a value to another fragment and just swap the internal pointer to the value. This might actually have significant perform…

"When all values are immutable, though, you can defragment the heap by copying a value to another fragment and just swap the internal pointer to the value." Wouldn't that turn shared objects into not-shared objects? Theoretically, that doesn't make a difference in a system without mutable data (assuming you leave out 'identity check', too), but in practice, it likely will blow up memory usage tremendously. Edit: I th…

http://en.wikipedia.org/wiki/Cheney's_algorithm Is quite common in systems and uses "forwarding pointers".

Re: An immutable operating system

#23

Post by _delirium »

eloff wrote: post #6

An operating system whose main goal is not performance is forever going to be a toy of professors. Linux is a mess compared to the beautiful code that would comprise this OS, but it's a mess that runs fast on real hardware and let's people get stuff done. That matters.

I think this is becoming less true: people are willing to trade off performance for safety and flexibility, given the right circumstances. For example, running everything inside of virtualized Linux instances is less performant than running in bare-metal Linux, but virtualization is nonetheless taking off like crazy.

Re: An immutable operating system

#26

Post by augustl »

mostly_harmless wrote: post #9

You mention that one of the benefits would be that memory can be shared across processes without any defensive copying or protection semantics, but isn't the entire idea that immutable values are a special type of defensive copying and protection semantic? I imagine that this would be useful if doing many calculations on readonly values, but would take a performance hit for readwrite operations. I'm not one for purel…

Interesting definition of immutable values, and a valid one. My perspective is different. An immutable value has a value add more than that of avoiding defensive copying, such as structural sharing. When you add a key to an immutable map, the new map can point to the old.

It has become more and more common to model systems with append-only as the only form of write (Event Store, Datomic), so readwrite can probably be avoided in some cases. And things like IP packets certainly makes sense to represent immutably - anything else is a bit of a lie :) But there is certainly a risk that the trafeoff of immutabulity becomes too costly for an OS..

Also, the system language will not be pure, like Haskell. Just immutable values, like Clojure :)

Re: An immutable operating system

#27

Post by augustl »

mtrimpe wrote: post #3

I gave an un-conference talk at Clojure days Amsterdam called "Purely Functional OS" on this exact topic and we had an incredibly interesting discussion about the topic. The conclusion we kept coming back to is that it's technically not all that difficult to implement, but that to make it usable in the real world would mean that computers would have to get a lot more cautious about source vs. derived data. The main t…

Very cool! "If you're the only one with an idea, it's probably a bad idea" :) Feel free to e-mail me, would be lovely to join forces.

Re: An immutable operating system

#28

Post by RivieraKid »

I've always been baffled by Clojure's view on state. It seems like just a rename of the concepts present in most languages today. Ie atom is mutable variable and value is an immutable value. What's the novelty here?

Re: An immutable operating system

#29

Post by barrkel »

RyanZAG wrote: post #14
stcredzero wrote: post #7

A garbage collector that knows that all values are immutable will be rather interesting, I think. Typically, a garbage collector will stop the world (i.e. halt execution) to do heap defragmentation of the old generation. When all values are immutable, though, you can defragment the heap by copying a value to another fragment and just swap the internal pointer to the value. This might actually have significant perform…

I don't see how immutability makes much difference to garbage collection. Garbage collectors don't look at the value inside memory they are collecting, only whether something live is still retaining that part of memory. Whether the value is mutable or immutable has absolutely no bearing on the performance or logic of the GC. Either something is still using the memory, or it is free to collect. Also you've just descri…

Generational GC usually depends on write barriers to detect creation of references to newer generations inside older generations.

Immutability prevents the mutation of older generations, so no new references can occur.

So I expect generational GC to be easier to implement. I wouldn't expect it to be faster or slower though, because programs will need to be written differently to cope with the limitations on mutability. O(1) algorithms will likely be replaced by O(log(n)).

Re: An immutable operating system

#30

Post by ksk »

eloff wrote: post #6

An operating system whose main goal is not performance is forever going to be a toy of professors. Linux is a mess compared to the beautiful code that would comprise this OS, but it's a mess that runs fast on real hardware and let's people get stuff done. That matters.

The goal of Linux was not performance, it was to create a free OS. The fact that it has become a high quality performant OS is a side-benefit (driven by external commercial factors, much later in its development timeline).
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