Month: April 2005

Extending using Wrapping

Ever had a problem, not being able to add more functionality to an existing class? Some languages seem to support adding functionality to an existing class but it does make it less secure and leaves a lot of dangers of maluse.

A solution could be to create a new class which inherits the original class although it can only be instanciated using a cast from an instance of the original class or instanciating providing the original instance. Also it won’t be able to override anything otherwise it couldn’t act as its base object.

A possible implementation of this idea could be:

wrapper Int_IsOdd : int {
  public bool IsOdd() {
    return this % 2;
  }
}

And it could be used in several ways:

int myInt = 100;
print ((Int_IsOdd)myInt).IsOdd();
print myInt.IsOdd();
print new Int_IsOdd(myInt).IsOdd();

The first way would be the easiest for both a reader which isn’t familiar with the extension and for the compiler to guess errors. The second would be neat to use but it would be confusing for people that cannot access the rest of the source or do not know what function is meant. The third way would be very compatible.

I wondered by myself whether normal inheritance could provide this functionality.. and it does. The only problem is that polyforism only works up and not down as the wrapper requires. (when you got a class a and b inherits of a, you can with inheritance treat an instance of b as a but you cant treat an instance of a as b which is required for the wrapper)

Also a wrapper would be more cached and not really a new instance as suggested by the way it seems to work and can already be slightly implemented in existing languages.

Maybe it’ll be put in paradox.

update – I talked with Kaja, and it will most likely be a feature of paradox

It’s all about the model

With all those strange new physics theories and models which seem to conflict eachother it seems all rather too awquard to be true.

Like Quantum Mechanics stating that something can be two things at the same time, which seems impossible, but certainly is when keeping in mind that Quantum Mechanics states that something is what it seems to be when measured where measurement always has to interact which means that very unstable states of an object don’t exist but still can be applied on an object being two states at the same time with a third set of properties… great…

What people don’t seem to realize is that most physics theories apparently conflict for they are formulated rather awquard, but only formulated like that for then they are reasonably understandable as a model. Also one given theory isn’t superior above another, usualy one theory just stresses a certain part of apparent reality more by the way it represents everything.

There just isn’t the theory that explains how the universe works, there are only models covering a part in a certain way.

I don’t care if someone likes to represents an atom as a little UFO, as long as the conclusions and predictions in that theory are usefull in being able to predict behaviour and characteristics.

This is also where philosophie makes a fatal mistake, a philosopher would tend to use metaphores, scientificly called models, literaly assuming that reality is just a metaphore. And there ishardly anything you can do to persue them otherwise anyways :-).

Apparently it seems, assuming the string theory is an accurate model, that we only experience an infinite small amount of the whole universe. It maybe could be seen that we are just a little (end) fractal in a big fractal (inside another).

But why are we as we are? It would be logical to assume that we are nothing more than a logical result of one chaos like formula for the whole universe seems to be pseude randomly as many chaos formula’s seem. We’re just one of the infinite possibilities (stressing possibilities).

That would seem rather depressing and our lives would seem rather useless.. and actually.. they are rather useless for the whole static everything. But actually that makes just one more reason to maintain our human species for otherwise we couldn’t enjoy our uselessness :-).

And even if we would have to formula to predict everything (which maybe even has been found already by some mathematician, but is only experienced differently by us as models differ from eachother), we would only be interested in derived models for our perception of it to aid our uselessness :-).

The Linux Paradox

Linux wants to get popular. Everyone using linux wants linux to grow bigger and bigger to ultimately have linux be the operating system dominating. err.. correction.. independant distributions and inheritances of linux to avoid the nasty monopoly stuff. Even your mom should start using it.

Sounds good. Even if linux is in some people`s opinion not the best OS it still has the best community backing it and is the most secure OS. It also has got the most support from the community. If something is required or has to be fixed it`ll happen in notime.

So why doesn’t everyone use it already?

The problem is that linux demands too much from the user.

A linux user should be able to at least have a grip of how a console works. And preferably has to know how to compile application and fix bugs when it won’t compile. And a user should know how to get dependencies it misses. An user should read through the fast different documentation of each application to even begin to hope to get it running easily. And an user should start over every time a new version is released.

Sure, they got RPM’s and yumm which makes life a lot easier. But the yum repositries don’t contain everything. If you want some new stuff, or an application with a certain module installed you have to go dig into configuration files, master the console, read through documentation, compile, and offcourse check your version dependencies, etc.

The average windows user like your mom doesn’t even know how drives work and certainly have never heard about the command line. It just wouldn’t work out. They got a lot of trouble even with just one or two options. When confronted with linux with hundreds of possible options and even stranger errors it just won’t work out well between them.

It certainly is possible to stick to the main applications provided by your redistribution and using the yum repositry. But linux will never run as satisfying as when you get it all compiled yourself and configured yourself. This really makes a big difference! I made linux start up a lot faster by compiling the kernel with only the modules I require with computer specific optimalizations. These little things give linux a really big edge over windows.

Linux is and remains only interested for adventerous ‘power’ users with quite some free time on their hands.

Don’t rely on parsing

Most applications store their settings (espacially in *nix) in text configuration files. These text files need to be parsed every time the application starts.

Parsing is the action of (usualy streaming) dividing a certain piece of data into understandable parts. This usualy comes down to looking at the text file character by character and deciding what should be done. Usualy this is done by maintaining a state which contains the data collected sofar. And with a bit more complicated files this even means having a stack of states and complicated actions when a certain state is left.

The problems:

  • Parsing is slow, very slow
  • Formats required to be parsed contain overhead, a lot of overhead

But it certainly has got advantages:

  • Humans can easily edit it, you don’t need to rely on configuration tools
  • (Usualy) makes a configuration format more extensible by nature (adding one new field in the average programmer’s binary format would break it)

Now, there are attempts to help improve speed. This by standardizing the format, which makes the amount of oddities to expect less, which ultimately makes the whole parsing slightly faster. This at cost of the easiness it can be edited.

A good example would be Xml. Xml is damned ugly. Xml is too strict. And Xml still takes a hell of a lot of time to parse.

Yaml looked like a decent alternative: easy to edit, looks nice. But then I encountered this:

%YAML 1.1
---
!!map {
? !!str "sequence"
: !!seq [
!!str "one", !!str "two"
],
? !!str "mapping"
: !!map {
? !!str "sky" : !!str "blue",
? !!str "sea" : !!str "green",
}
}

Ugly…

So what to use instead?

Use binary configuration files, which are easy to load and save for the application. And create a parser to parse the configuration file and save it to the binary format! In other words: serialize the usefull data from the parsed document and only parse again when it is required.

When you only parse stuff when it has changed by the user than it doesn’t really matter how long it takes to parse. Which can get rid of the really ugly stuff and let us just have a very loose kind of format without the ugly rules and regulations.

‘Objects’ in C – Part 3

In Part 3 of this mini serie I`ll discuss how interfaces / (multi)inheritance like behaviour can be achieved in a language like C as in C++.

In the posts before (part 1, part 2) I discussed the possibility to inherit behaviour of an ‘object’ in C by adding a type pointer which handles initialization and destruction of the object; achieving the possibility to extend an ‘object’ by adding fields at the end and updating the type pointer to a new type.

Any object contains a pointer at the start to its type. The type of an object is passed to the CreateInstance function when an instance needs to be created of the object. The type itself just contains a few fields:

  • Length, the required length of the object, this allows an inheritance to extend the amount of data.
  • Constructor Function Pointer, the Constructor Function Pointer is called after the object is allocated to construct its contents.
  • Destructor Function Pointer, the Destructor Function Pointer is called before the object is freed to destruct its contents.

These fields, along with using function pointers in the instance itself instead of functions, allow an inherited type to expand the existing type. The problem is that an object can’t inherit from more than one object, for both object’s expect to start just after the pointer to the type. To solve this an additional field needs to be added:

  • QueryInterface Function Pointer, the QueryInterface Function Pointer can be used to get an instance of a supported type from the instance called.
  • Top Object Pointer, the Top pointer points to the top object. (An object returned from QueryInterface its Top pointer would point to the object where QueryInterface was called)

nb. The latter one will be added after the type pointer in the instance instead of in the type

A good example would be a type called ICloneable which itself only contains one field: Clone, a functionpointer to a function to clone the object. When you would want to clone an object given you would use:

ICloneable* interface = toClone->top->type->QueryInterface(toClone->top->type, toClone->top, ICloneableType);
Object* clone = interface->Clone(interface);

Lets take a look to the first line:
ICloneable* interface = toClone->top->type->QueryInterface(toClone->top->type, toClone->top, ICloneableType);
This line queries the interface that the object that will be cloned wants you to use to clone it. The top object is used for that is the only way to be certain that you are dealing with the top object and the latest code instead of some base. Using this code an object can be cloned by just providing its interface!

(the QueryInterface takes 3 parameters: first one is the type itself where the function pointer relies, second is the object in question, third is the requested type where ICloneableType is an instance of the ICloneable type).

Object* clone = interface->Clone(interface);
The second line just calls the functionpointer in the interface queried.

To ensure that every bit of behaviour can be overriden, the object queried using ->top->type->QueryInterface on the provided object must be used instead of the provided object itself for the provided object can be a whole different object merely supporting that interface secondarily.

The nice thing about this architecture is that a top object merely wraps its implemented objects and returns them (possibly addapted) when queried for it. This allows way more access to the inherited types than in any other object orientated model.

This model is quite easy to implement in C and (I hope) will be easy to intergrate with for instance objects in a Virtual Machine.

How to GC in C(++)

GC`s, Garbage Collectors, are systems to manage memory. Even the good-old C-runtime library has its GC. free, malloc and the others. Now, these aren’t the best memory managers there are. They cause fragmented memory, and scatter the memory of your application over the whole memory rendering the great processor l1 and l2 cache almost useless.

I won’t talk about how to use the C ‘GC’, but how to implement new-generation alike Garbage Collectors in C(++).

The best GC`s can be found in Intermediate Language Virtual Machines which keep track of every object`s type in the memory and can therefore freely move objects in the memory. The great advantage of this is that object that have survived about as much Garbage Collects tend to link a lot to eachother and use eachother. That group survivors is called a generation. When you put a generation close to eachother in the memory, it will usualy only take 1 RAM memory load for the CPU, caching the whole generation in the CPU cache, for a while which is a lot quicker considering that l2-cache is about a thousand times faster than normal RAM.

The problem in C(++) is that you can’t just move objects. You don’t know what part of the memory of an object is a pointer, and what is just a mere integer. Therefore it is impossible to make a generation based Garbage Collector for you just can’t move stuff.

Allocating a big chunks and putting the objects of the C(++) application however using a custom allocation function will generate some additional performance above the traditional malloc although it still isn’t perfect.

One way to get it to work is to let the GC know what a pointer is and what now. This can be done by letting the first 4 (or 8 bytes in case of a 64bit CPU) be a pointer to a function which returns an array of offsets which resemble the pointers in the type.

Now the GC knows what the pointers are in a structure :-D.

The GC can now move the object by updating the pointers from the other objects to the new location of the object!

The only problem with this is that there can’t be pointers to the object, or inside the object from a not referenced pointer exposing object or a object that doesn’t exposes it pointers at all.

To overcome this I guess it could be feasable to add a flag byte in each object that exposes it pointers which allows it to specify a function that can be called when moving the object or when an object referenced is moved.

I’ve tried out some ways to get this all wrapped up in a nice framework (which is very feasable using my ‘objects in c-framework’ or something similar (easier) in C++ using inheritance).

I`m afraid however that such a GC comes too late for by the time it is reliable the Intermediate Languages would have gained way more ground for these can implement way more optimalizations, including in the GC, during runtime for they tend to use an Ahead of Time and Just in Time compiler.

Feedback on this would be welcome :-).