Conceptual Walkthrough: Distributed Applications

It may be surprising, since I am here to talk about distributed computing, but I hate process forking - making copies of a running application, each running the same code but each dedicated to a different task.  I'm sure I'm not alone in this, because it's not as though people are running around calling fork() for every little thing; multithreaded and multiprocess apps are not exactly common, not unless you're doing something that really requires such a technology.

Frankly, it's a headache to try to understand.  In theory, it should be simple; there's a copy of your program, but you know which copy is which, so you just do different things with them.  If before that, you open up a pipe, both copies of the application will have access to the same file descriptor for that pipe, and they can communicate through it.  But all of those things being technically possible isn't a plan.  When that pattern is laid out in a book, it leaves you wondering: what am I supposed to do with it?

I talked in several places about programmers being obliged to reinvent the wheel, and process forking is a good example; forking wouldn't be such a terrible thing, if it was paired with a functional remote procedure call mechanism.  When two copies of the same program are connected with a pipe (or two), you can use it to pass data, but that data transfer is mostly pointless without context.  Adding context, labeling the data, makes it essentially a very simple, poorly implemented remote procedure call, where the "function" that is being "called" is simply an index specifying what to do with the data, out of a set of options fixed at compile time.  While process forking would still be a bit confusing if the process forking mechanism came with a built in RPC mechanism, at least the programmer would not have to wrestle with all the complexity of implementing their own RPC stack from scratch while also trying to build program logic around it.

Although I wasn't thinking of it when I designed the system, the ADA distributed applications model is basically exactly this, and to help you understand it, let's walk through the analogy a little more closely.

As I see it, forking has two fundamental problems with it; first, the fork is undifferentiated.  It is easy to overlook the fact that it is a feature of programming languages that we can attach variable names to data in the first place; when I say that forks are undifferentiated, what I mean is that this deliberate feature and mechanism of programming languages no longer functions.  In each half of the program, a large number of symbols exist but point to the wrong data, and it is entirely up to the programmer to recognize this and keep track of which symbols are now incorrect.

This is in fact the reason why I have specified that under the ADA, programs should be written and compiled such that each module which is to be depoloyed separately, shall have its own variables confined to a single namespace.  Namespaces in this context may be nothing more than a collection of variables given a group name, but for our purposes, it draws an explicit distinction between what is, and is not, accessible within a specific context.  You could, of course, do the same thing with a general forked application - but it still leaves us with the problem of needing to create a new remote procedure call mechanism.

Let's take the "remote" part out of the equation for now, and only talk about a forked application communicating with another copy of itself.  A procedure call mechanism in this context is a pipe that you periodically check (or block and wait), looking for a data stream in a fixed format.  That data stream will tell you what function to call, or what variable to write to, or what variable to read from, and it may also include parameters for the function (or an index to an array, etc) and then you return any out-values through the pipe to the other side with a similar mechanism.  Likewise, the calling side of the pipe will send a packet in the expected format down the pipe, and then block and wait for a return value (or merely an acknowledgement that the function is being run, or that it has completed successfully, depending on the context).

You as the programmer will most likely want to select some highly specific subset of functions or variables that you want to use with this mechanism - when building it yourself, you will most likely only accept some very few "commands" that you listen for and respond to from the other half of your application.  Because both halves are the same applicaiton, though, you could also use a lookup table that lets you unambiguously access any variable or function present on your half of the application - there are, after all, a fixed number of those functions and variables, and you know for a fact that all of them have unique identifiers, because you use those unique identifiers while programming.  And once you have selected a function and/or variable to access, any parameters that get sent along by the request can be type-checked, because you know the method signature or variable type.

Doing all of that work by hand would be an awful experience, and most if not all of that hand-done work would be wasted, as you are unlikely to call most of the functions or access most of the variables.  If however, it were a function of the programming language, compiler, and linker - that is eminently possible, because that is, essentially, the compiler's whole job.  Translating an identifier to a function, checking the number and type of the parameters, all of that is necessary to create the program in the first place.

Suppose, then, that you had a compiler that created an indexing function.  These kind of functions exist, when you use reflection tools - the indexing function would take a variable name or function and some arbitrary parameters, and call the function with those parameters, and then the indexing funciton would return the variable or return value when it's done.  Let's suppose at first that exactly one indexing function is created for your whole program.  You as the programmer might simply pass anything that comes down the fork pipe to the indexing function (unless you just called a function, in which case you would wait for the return value and parse that) - in fact, ideally, there would be a built-in function that just reads commands from the pipe in exactly this way, and a paired function that writes to the pipe in exactly the way the reader expects.

This is still relatively unsafe; there is a lot of potential for race conditions and so on, and there is nothing stopping you from requesting data from the fork that is actually stored somewhere else.  But assuming you had some need to fork an application and run it, this reflection-based indexing function would free the programmer from having to figure out how to pass messages back and forth, free them from having to write any middleware, and simply allow the programmer to use the capabilities of the other process, its data and functions.

But let's go back to the namespace thing.  You see, we are still left with the problem I started out on - that a forked process has duplicate identifiers, half of which are simply wrong, because the actual memory location where they are stored is in another process.  But, you know which process they are stored in, and you have a well-established mechanism for requesting data or calling functions in that process.  If you knew for certain at compile time that some subset of those identifiers would be in the forked process, the compiler might translate any requests for those identifiers to instead use the pipe-send function.

But wait, there's a problem: both forks of the application are running the same code, so at compile time, it's impossible to distinguish whether the request is going to be requesting data from the original or forked process.  This is where namespaces come in - you may not know whether a given namespace is in one process or the other, but you should know for certain that the contents of a specific namespace will all be in the same place.  It's only when you exit the namespace that there is any chance you will be trying to reach data that exists in another process.  That's simple, then: in the forking function, allow the programmer to specify which namespaces are being detached, resulting in two collections of namespaces, one associated with the original process, and one with the fork.  This will be a runtime check, in case there is any reason to change which namespaces get separated in different circumstances - because it is a runtime check, a checking function will be called every time any bit of code requests data or functions outside its own namespace.  (There are ways to reduce the overhead, but ignore that for now.)

Well, if you can do all this once, why not do it multiple times?  Say you have a program with five total namespaces and you want each in its own process.  There's no reason why that should be difficult, should it?  You would simply need the runtime check, the one that knows which process contains a given piece of data, to also select the appropriate pipe to use.  There is, admittedly, one complication - making sure that all forked processes receive updated routing tables - but since you've built a robust framework for sharing data already, that hardly seems like much of an imposition.

It's worth pointing out, though, that if this system works correctly, it should also work correctly if you never fork the application at all.  In that case, there is no confusion about which process owns which variable - all of them are stored in the same process.  So, your program will truly not care whether it is currently running in a single process, two processes, or five processes; when you as the programmer insist on calling a function or fetching data, the function will be called or the data fetched, no matter which process currently stores that particular piece of data.

Now, forking a process is necessarily something that happens in the same place where your application currently is, which sharply limits the usefulness of everything I've just described.  Not to say that it's useless - I think anyone who is interested in forking processes would appreciate having all of this functionality - but what I've just described is not actually the functionality that I want from the system.  A distributed application, as I've described it, is one where this forking process happens between two computers - where you can run part of the program logic on an entirely separate machine.  And conceptually, once you've done everything I've said above, that's not actually a difficult proposition... to an extent, at least.  You need some permissions, and you need to make certain that dependencies and the like are synchronized, but the technicalities of starting a process somewhere else, and binding a pipe that connects the two processes over the network, are not particularly difficult.

I've said this in other places, but to reiterate here, the value of doing this fork over the network is allowing your program to place specific bits of code where they are needed, without the program itself needing to care that those bits are not on the same machine.  Generally, these "specific bits" are in one of three categories: input, output, or computation.  The benefit I'm talking about is not accelerating your program with parallelization (you can do that if you have a whole lot of computing to do).  No, the benefit I'm talking about is a kind of program that we don't currently possess - one that replaces the idea of remote desktops and SSH tunneling with running an application in one place, and handling the input and output in other places.

This category of applications is something that should be simple.  If you want to edit files, you generally want the file editor to be where the files are, because it will involve a lot of reading from and writing to the disk; compared to that, GUI updates and keyboard and mouse inputs are much less sensitive.  I for instance have an NFS volume that holds many of my files attached to this computer, but if I want to unzip files on that machine, I tend to open a remote shell and perform the action local to where the files are, rather than having my desktop wait on network traffic in both directions for every file operation.  Likewise, some tasks that depend on accelerators, such as video editing, are best done when the data and the accelerator are in one place, but that doesn't necessarily require that the user is in that same place.  As long as input and output latency is within acceptable parameters, you can do a lot remotely - and it's only easier if the entire output stack is being run on the machine closest to the output itself, for the same reason.  A lot of system GUI updates, especially, are highly redundant; you can summarize the changes with a few bytes, while a single new image frame may be several kilobytes, and sending every single frame in an easily-reproduced GUI animation may be millions of times more expensive than doing it locally.

Instead of asking what is required to live in a world where this is possible, it is better to ask why we don't.  The legacy of computing simply assumes that everything will be in one place, and comparatively little of our development has been focused on splitting a program up into pieces distributed across a larger system.  We are encountering this need more and more, and so more and more people are getting exposed to it, but until the default way we write programs allows this kind of cross-computer access natively, accessing a program running somewhere else will continue to be a tedious affair.

And to be fair, this "conceptual walkthrough" is more difficult than it sounds, in that it requires tweaks to compilers and programming languages, on top of providing a mechanism to deploy those forked programs on another machine.  Those things happen, and there are experts in those fields, but if anyone is wondering why I haven't written my own code... rewriting program languages is simply a task that's beyond me!  Tasks that are much simpler for the compiler and linker would be an enormous headache to write by hand, but that doesn't mean that it's easy to change how compliers work.

But for the people who actually know how to do all these things... I imagine that if they just knew what they were trying to accomplish, they could change the world.  There is a lot that's possible, but which simply won't happen without the right support and tooling.

Half-MAD: A Shorter-Term Vision

 I think that one of the reasons why it has been difficult to enunciate exactly what it is I want project MAD to accomplish, is because to an alarming extent, I want to do things that we are not doing in a modern machine, but extended to encompass all of several machines at once.  Thus to my chagrin, I end up effectively making a list of demands that might be considered absurd if they were to happen in a contained, well-understood environment, and then adding “…to everything, everywhere” at the end of the list.  And to be clear, Computer Science as a discipline is well versed in problems that do not scale well.  Proposing something difficult and then demanding that it scale is, itself, extremely arrogant.

The only reason why it doesn't approach being farcical is that I am proposing each sub-project with methods already in mind, if not in hand.  Ultimately, when it comes to actually implementing the ideas, new problems will crop up that we have never experienced before.  But to better understand why those projects are worth the problems they cause, it's worth discussing some of them in a smaller, more general context.

What is a Device and What Do They Do?

I talk a great deal about how Project MAD is designed to let you access devices or resources or capabilities of multiple pieces of hardware.  This is a strange topic for an application programmer; if you haven't already delved into microcontrollers and peripheral interfaces, you may wonder why anyone would care about all the devices attached to a system anyway.  When all you are doing is building some random bit of application logic and wrapping a user interface around it, using fixed and well-defined OS concepts or third party libraries, well, if you end up needing to talk about drivers for literally any device then someone has done their job wrong.  And indeed, if I wanted the average, user-facing application developer's life to change, I would probably be making their life worse, not better.  Part of the design of MAD/ADA is that, in fact, they don't need to worry about devices.

But also, devices will absolutely be used to control how their application works and how it is distributed across the system.  That's all fine, assuming they don't have to worry about it - but of course, eventually, a professional developer will run into every bug that comes within a mile of their code, let alone the ones actually inside it.  So if they do, technically, need to worry about devices, it's worth asking: what are they, why do we care, and what do the changes I'm making actually do for us?

Obviously, at its simplest, a “device” either changes the world outside the computer, or produces data based on the world outside the computer, or else it makes some data-to-data transformation task easier.  Those are, basically, the only things a device could even possibly provide: output, input, or services.  If you want one of those three things, you are going to be touching a device, even if that's only with an OS-standard ten foot pole mounted to the nearest wall.

An application developer's life is usually pretty simple: if we need input, we take it, if we need to output, then we output, if we need some service, then we talk to it.  Usually, someone else simply handles these things, in fairly standard ways.

The trouble starts whenever the OS itself either doesn't care about a device, or makes faulty assumptions about how you want or need to use it.  Say you have a TV across the room and you want to cast video to it. Modern OSes tend to only do two things with monitors: extend the desktop onto it, or copy some other monitor's output onto it, and neither of those may serve your needs well.  That's why in 2013 Google put together a tiny little dongle with a surprisingly important feature: you could just send video to it.  It took input and produced output, entirely separate from the normal desktop (or phone) metaphor that we had become familiar with.  And while I won't say that has or hasn't changed the world, I for one am grateful for such a device.

You can understand devices like that with a simple, generic model.  They have some requirements (the Chromecast needs internet and video out), have some capabilities (it will display internet video streams on the TV), and have some way to control it (a remote, or network packets).  When I talk about devices, I pretty much mean anything that fits that, extremely broad definition of input, output, and control.

So it may surprise people who don't look at how OSes work that an average programmer probably doesn't know how to get a list of all devices present on a given machine, can't tell what a random device is capable of, and can't figure out how to control that device.

On all major operating systems today, the device model can generally be broken up into two categories: if the OS itself uses it, then the OS takes care of it and you live with the OS model for better and for worse.  Otherwise, it may be technically available but you'd better find a library or application that knows what it is and how to use it, because they ain't touchin' it.

And that's… that's kind of it.  There isn't a whole lot of nuance here.  Either the OS takes care of it, or you're on your own.  There are some cases that are better or worse, but broadly… yeah.

Why?  Well, that's not hard to understand.  Someone has to invent a way to deal with it.  If that someone works for Microsoft, then Windows can handle it; if they work for Apple, then Macs can handle it; if they enjoy open source projects, Linux can probably handle it.  If they are part of some other company, such as the manufacturer of some device, they will provide an application and/or library that works and consider their job done.

Unless the device is really, mind-bogglingly important (and/or you convince people that it is), nobody is going to reshape how the OS works in order to help your device fit into the ecosystem better.  And… it has been that way since the dawn of computing.  Generally speaking, everyone involved would rather make small changes than big ones, not least because if you make big changes, consumers may not like it and you may be out of business in anywhere from two months to five years.

Something like MAD's OS project doesn't necessarily need to reinvent the wheel so hard that it changes the way the world itself turns.  I may end up sounding like that's what I'm doing, because I want to paint a picture of what MAD is capable of, but you could just… add some of MAD's features to existing OSes, or as a third party structure on top of them.  To wit, devices.

But first: IPC.

What is IPC/RPC and Why Should I Care?

Inter-Process Communication and Remote Procedure Calls are both fancy ways of saying that two programs talk to one another.  Generally, IPC is happening among two programs on the same computer, and RPC is the same but going between machines; there are some differences there, including important ones, but let's set that aside for the moment and just talk about how computers work in general.

I said in the last segment that you can divide device support into “The OS Does It” and “You're on your own”.  Categorically, the same is true with talking to other programs.  If the OS does it (and by it, I mean, making some given program do something specific for you), then there is a function, one that probably works very similar to every other OS function that you have had to use while learning to program, which talks to that system program and then gets back to you.  If the OS doesn't care about that specific thing, at best you will find a library or programming language that makes the task of talking to some specific programs just as easy.  (There is an aside here for scripting, but that requires a whole ecosystem to set up and so, like OSes themselves, can be difficult to make pivot if a change is necessary)

However, it is at least as likely, if not more, that you will have to do a whole lot of research into how that specific program works and how developing IPC/RPC mechanisms work in general and then you do a whole lot of work to make the mechanism talk to the specific program, and oftentimes, talk to a specific version of that specific program, because that might change.  And this is why we have kind of standardized on IP and web services nowadays - everywhere you see them pop up, there are a whole lot of tools that almost everyone involved did not need to invent.  Reinvent, sometimes, but not from scratch.

IPC/RPC mechanisms, however, do still need to be made.  If you have a program, say, one that takes your company's new fancy keyboard with per-key LED lights, and exposes the light-output capabilities of that keyboard to the user (letting them make all the colors their own brand of pretty), you will probably not design a server into that program which lets other programs talk with it.  And why would you?  That sounds like a lot of work!

But look at it from another app developer's standpoint - if they want to make a key flash when a notification comes in, say, they have three general options: learn how the keyboard driver works (which may be, if I may summarize, very custom), interact with the manufacturer's application (which we just ruled out), or interact with some third party library which can do one of the other two options for them.  If nobody has or wants to make that third party library, they're also out of luck.

MAD takes a tact that may be very alarming, which is that all programs should by default have some IPC mechanisms - it's part of making them distributable across multiple pieces of hardware, after all.  But you could also… you know, just, use that same mechanism to expose some functionality.  That exposure doesn't need to be reckless; can maintain some controls, make sure the user is involved, something like that.  But if we decided that IPC/RPC should be easy, maybe we should expect you to interact with other applications more often.

And the point of deciding that it should be easy, is that having made that proclamation, there ought to be a very standard way to do RPC, such that it is just as easy to work with as when the system takes over handling that task for you, because you're talking to a system component and they know how to do that.  If we want programmers to take it at all seriously, you have to make it easier for programs to interact fairly regularly.

And if you're going to interact more often, it might be best to have standards for communication.  And if you wanted, perhaps, to make that OS/DIY dichotomy even less severe… then OS IPC should work in the same way general application IPC works, adhering to the same standards.  That way, people who are forced to learn OS methods when they start programming, don't need to learn a whole new separate thing when they start dealing with new and more interesting tasks.

Which brings us back to devices, or rather, device drivers.

Making Devices Accessible: The System API Directory

Again, this is all stuff I've talked about before, but let's dial it back.  You have devices on your machine.  How do you interact with them?

Well, generally, every device you'd like to talk to exists on the far end of some kind of connector, and what is exposed at the very bottom of the CPU/Kernel system is the near end of that connector, not the device itself.  Many of these connectors require a little bit of finesse to use properly, so there may be a relatively complex driver just to ensure that any message you send across that bus gets where it's going, meaning you will be using a slightly higher level API that accounts for the bus itself.  Only once you are in contact with that other device can you talk about, you know, talking to the device itself.  Now, modern CPUs aren't just big-banging busses (meaning the CPU itself isn't hot-looping to make sure that every bit gets sent at the correct time, or anything similar); they use support chips, microcode, and other conveniences that might be relatively specific to the processor/motherboard combo you are using, but there are standards and firmware to sort of even out the complexities of making that part of the system work.

Once you can talk across a bus to a device, you have to know what language it speaks.  If you know exactly what device you're talking to, this shouldn't be hard - the manufacturer should list all the commands, what they do, what the return data means, and so on.  A few manufacturers prefer to keep some secrets… but let's not get into that.  Some things that you will be interacting with on the other side of a bus are themselves programmable, and you may be sending code to them (which is a whole other thing that is only partly covered by MAD/ADA), but frequently, you are just issuing commands that make it do whatever it is you want to do, and listening to the bus for both expected replies and updates caused by an event.

The software which converts requests from a programmer to commands that arrive at the device, and responses from the device to normal software events and function returns, can be understood as drivers.  This is where the OS/DIY dichotomy comes into play: the OS will keep track of devices it cares about, and ensure that there are very standard ways to interact with drivers it cares about.  Devices that the OS doesn't care about are not well kept track of, and the ways to interact with them are not terribly standard - at least, not outside of the specifications of whatever bus they are on the other side of.

The MAD/SAD proposes to tackle these two problems at the same time.  It asks device drivers to expose a standard API and an implementation library; programs that utilize the API can link to that library and they will be interacting with the device itself.  Then, all device drivers are listed in a filesystem directory, indexed by a key representing the API, and linking to that library.  If more than one device implements an API, even if they use the same library to do so, the implementations are listed separately and configured differently, so when your app links to a given device's library, you will be talking to that specific device when you make API calls to it.

That on its own represents a massive difference to how libraries and devices exist in any modern operating system.  Today, libraries are just things that may or may not exist, and devices are just things that may or may not exist.  You can't just link to a library and be talking to a device - you link to a library and then it will let you ask the system if any devices exist, because the library itself isn't configured, but is instead generic.  Likewise, you can't just point to a device and get a library that interacts with it.

When I talk about “You can just add shit from MAD”, I'm talking about shit like this.

But I go a little further with MAD/SAD.  I mentioned the libraries are indexed by an API key (in the filesystem, but you can ignore that for the moment), and if you've read any of my articles, you know that the API keys are in a tree, corresponding to an inheritance model.  And since I'm trying to explain all this simply, let's touch on that for a moment.

The API itself promises that the library attached to it will have certain functions; if you call those functions, you will get certain results, and the API makes all that very clear.  That doesn't mean that those are the only functions in the library - it's only a promise that if you go looking for certain ones, you will find them.  So naturally, a library may implement more than one API, each time exposing different functions.

Likewise, an API may provide different levels of what amounts to the same API.  It may provide a dirt-simple one, and a slightly more complex one, and then a far more complex one.  Generally, the simplest one gives you the fewest ways to customize it, but it also means you need to know the least about what kind of specific device you're using; the most complex one requires you to know exactly what the device is, but may essentially give you direct access to everything the device is capable of.  Since you choose the API when you write the program, you get to decide how specific the API you're targeting is.

Thus, in the MAD/SAD API tree, the folders closest to the bottom of the tree contain very simple APIs that require you to know very little about the devices, and which apply to far more devices, but which also expose very few features - and then there are more complex APIs that require you to know what you're asking for, but give you more control, until eventually you get to a library which may provide you direct access to the device with no hand holding whatsoever.

But in an inheritance model, you don't necessarily hide the API that came before - the parent and child APIs coexist, and the child API is obliged to expose every function the parent does.

Suppose you have a device that acts as a source of character data - that may be, for example, a keyboard, but it also describes files, network streams, and some busses like serial ports.  In any of those cases, the API will provide you with a generic “read” function that provides you with a “firehose” of data sent directly from the device, and probably also a generic “write” function to shout character data back down the pipe to be heard at the other end.  Questions like “What does the data mean?” and “What should I say to this device?” are not answered at all by this level of API.  If you use that level of API, you will not know what device is on the other end, or if there even is a device at the other end, not when you are writing the program itself - the user may know, but that's not your business.  Maybe the ‘device’ is not even hardware; maybe it's software, or maybe it's a black hole that says nothing and eats all input (aka /dev/null).

That same low-level API can be more useful to a programmer that knows what the device is, but when you know what device it is, you can usually also provide better service than just “read” and “write” functions.  Not always - some things really are that dumb and simple - but usually, you can provide an extension to that character device which provides new functionality.  Under MAD/SAD, that extended API will only be presented if the device promises that the library, and the device, implement those functions.  It will also still be listed among the low-level, raw character device drivers, because the extension adds to the lower level, instead of replacing it.

Suppose the character device in question your fancy backlit keyboard, for example; it may have three or four levels of API just in the ‘character device’ tree, to say nothing of (eg) a ‘raw usb device’ tree.  First, your keyboard is a generic character device; second, it is a keyboard (the output should be understood as keys, a keymap may be involved, and you can send commands to turn on capslock and so on); third, it may implement some standard “backlit keyboard” API, if there is one, and fourth, there may be a vendor-specific “This is our backlit keyboard” API that has some juicy extras the generic API does not.  This last API extends the other three; the third API extends the first two; the Keyboard API extends the character one.  But if you really want, you can just open the keyboard as a character device and listen to every keystroke that comes in down the line, and shout random character strings down the line just to see what happens.

Of course, the OS will recognize keyboards as something special, because the OS knows that most apps will care about keyboard input in one way or another - so it will make use of that second level of API (char/keyboard) automatically.  In fact it will probably create a virtual keyboard device that collects input from all keyboards (which should be a standard itself) and uses that instead of any specific device, because then the user doesn't need to change how anything is configured when they plug a USB keyboard into their laptop.  But the real point is, we have made the generic way to reach devices good enough that the OS can just use this tree to do what the system normally does, instead of making very unique and specific ways for the system to make critically important devices accessible, ways that kind of clash with how we program other applications.

Sounds nice, right?  Maybe a little boring.  But the way I introduced this topic was about APIs and libraries - it has nothing specific about devices in it.  Any persistent application that wants to provide an API and library can do so, even if it's not a driver or even a background service - and that application's APIs will be listed in the directory, same as any other.  So… if you install a new database service, say, you will be able to find it in the list of all databases on the system, even if that database is a foreground application for some reason.

Now, here's a funny little twist (which I've already talked about in another post): when you use IP and ports to connect to running applications and services, you normally locate services by a standard port number, because that's how it was when the internet was created.  Since more than one service can't share that port, other copies of the same have to have other ports; there isn't a standard for how to do that, so the user or service has to figure something else out.  You may be able to examine the other server processes and find out what ports they have open, or examine all opened ports to see if they sound like that service, but neither of those is a smooth, well-defined operation.  Under MAD/SAD however, if you know what API the service provides, you have a list of all of them that are running, and each item in that list is preconfigured to let you talk to it.

Moreover, you don't necessarily need to publish to the SAD globally.  Remember, I said the API keys are published in the filesystem; you might publish such a configured library file privately, if you had, say, an embedded database in a larger application, and you only wanted the parent application to talk to it.  Linking to that preconfigured library would connect you to the database; it need not be exposed to the network, or configured to deal with the network.  Presumably, an administrator or user could find it if they knew where to look, but that's about all the exposure it would have

The same mechanism that helps you find and utilize devices also helps you utilize things that are not listed?  Wow, it's almost as though it's just a better way to utilize things.  But what exactly is this mechanism?  I took it for granted that you can dynamically link to a library and it will be preconfigured to talk with a specific device.  That is… also not how things work.

Perhaps more to the point: Just before this I was talking about IPC/RPC and I never got back to it.  Why did I use that segment to introduce this one?  We already have dynamically linked libraries, even if they aren't preconfigured.  Making preconfigured libraries would be a fairly straightforward thing that has nothing to do with IPC/RPC mechanisms.

Well… the point with IPCs was that MAD argues every running application should expose IPC endpoints as default under MAD, meaning that if you write a service or application, you can interact with that application via another application directly.  Of course, if you want to interact with something via some IPC/RPC mechanism… you really should have standards.  Like an API.

What's the difference between calling a function embedded in a linkable library, and calling a function via an IPC mechanism directly?  Well… the linking bit, I suppose.  And it matters exactly what application and user is “running” the code, as far as the system is concerned.  But if the library mostly exists to provide a translation layer, between the published API and IPC endpoints exposed by a service… what if there just wasn't a need for a translation layer?  Or rather, what if the “translation layer” was a bog-standard system call?

What if your client application, the one that wants to use the API, can't tell the difference between linking to a library and directly talking via IPC with a service?  What if the programmer involved need never care?  What if they simply… use the API?  What if they do so by using a system call that does whatever is needed to reach the target function?

Bringing It All Together (By Taking It Back Apart)

Now… Does this all sound like hyperbole?  Does it sound like I think this is all easy?  Because this isn't all easy.  Let's look back at a list of things described in this chain of logic that are new:

• Have all applications use detailed IPC hooks by default
• System call that translates API call into IPC to a running service
• Configuring linked libraries at runtime so that they point to a specific device or service, and using such libraries
• System call that translates API call to loading and running a configured, dynamically linked library
• The two aforementioned system calls are the same system call
• Listing APIs in a systemwide tree
• That systemwide tree is in the filesystem
• That tree is an interface-inheritance tree (or some other semantic structure)
• Allowing the API system call to be directed towards libraries that are not in the system tree
• The system uses the API system call for basic functions (where feasible)

Now, we could quibble, and maybe I've missed some small points, but if I have an idea that requires making ten changes to the way operating systems work, some of them pretty freaking fundamental, then you certainly can't take all of those changes and tack on to the end,

“Now do this for a dozen systems linked together into a gestalt system.”

Yeah, that sounds a little crazy, huh?  About that.

Anything, Anyplace, All at Once

Funny thing about those changes.  One of the key themes is that it lets you address and control devices and services as though they were files.  (In the case of applications, though I've not talked about it here, there's also a big portability thing so that you can run them from anywhere, but same basic idea - an application being accessible means it being runnable when all you have is the “file”.  See MAD/SAD AF)

The point of them being accessible as files was that it's not hard to have a filesystem that represents multiple machines at once - you basically just make a folder with multiple machines in it, and list out the contents of each machine under them.  That's literally all it takes; you can list the entire filesystem, or just what you think is important, or both in different places.  Sticking trees on top of trees… is just how trees work.

The question becomes: what's the best way to make use of that?  UNIX already has the general philosophy of “everything is a file”, so in theory, you could make a distributed system where they simply… all use a distributed filesystem listing all files everywhere all at once.  But first, modern machines don't actually stick to “everything is a file,” and second, sometimes interacting with things at the file level is very… back and forth.  Which is something you may not want to do over a network, where every back and forth has significantly longer latency than a local call.  Like… thousands of times longer, maybe.  And also, you would need some universal addressing schema for this multi-machine directory so that path strings work the same everywhere and are unique.

But anyway, so you want to do some things locally, to avoid thrashing the network.  That means running a program on the machine that hosts some specific device.  How?

We already have some technologies to do this, and the one that most people will be familiar with is the “serverless” cloud infrastructure made famous by Amazon Elastic Compute Cloud (EC2).  The point of the serverless model is that a program can be loaded on any machine that has room, and you just keep track of where it actually is loaded, so that whenever someone goes looking for it, you can direct them.  If that program is part of a larger structure, have it keep track of where other pieces of the same program are, in case they need to talk.

And that's basically the ADA (it's not, but never mind).  It's serverless infrastructure designed for an operating system and home network.  All you're really doing, is running a program somewhere else, so that when it access a file that is actually a driver or service, it is doing so locally instead of across the network.

And that's it.  With that, everything works!  Victory fanfare, parades, we all go home.  Right?  Well, sort of.  No, not really.

Clear the Air (Once Again)

You see, part of the problem with the ADA is that if you do it wrong, people will hate to touch it, let alone depend on it.  They will avoid it, frankly, because people are lazy.  And while you could, maybe probably, have the system still work when programmers avoid it, by doing a bunch of extra legwork across the network, if developers being lazy means that the experience sucks for the user, nobody will want to be a user.

Even if I'm right about how this all should work, if we do a bad job on the implementation, that's it - game over, we lose, things to back to the comfortable old ways with minimal changes.  That's why I did a lot of extra thinking about how certain things should work, most of which sounds crazy out of context, because I'm planning for a future where OSes work very differently than they do today, and then on top of that, computers are combined in some way that developers don't yet understand.  So if I were, today, to ask a developer to operate under MAD rules, or to just assume that my OS will work the way I say it does… they would be totally justified in telling me to piss off.

They'd have to be mad to believe in MAD, before it's proven.  And that's kind of the point, at least of this post.  Some of the things that make the MAD system work, might be implemented on top of a normal operating system.  The API inheritance tree doesn't have to be the only way drivers work; it doesn't even have to be the canonical system way that drivers work.  But if it's there in a form that people can use it, then other things I've said might start to slot into place.

Likewise, you can have an IPC mechanism that application use, which is separate from the normal system IPC mechanism - it would just have to use some higher-level mechanism, like an IP:Port interface, with extra code wrapped around it.  This IPC mechanism could let applications and services publish APIs into the same tree, and you could talk to them the same way you talk to drivers.

That thing about using a system call to reach the tree… well, if it's not part of the system, you'd simply have to use a standard server on each machine.  Aside from that (and it would be inconvenient), things could work about the same, with it farming API requests off to the appropriate source.

And the distributed, agent-oriented MAD/ADA programming model?  Part of its genius is that you don't write drivers and services to listen on the network - they all expect to be contacted by a process on the same machine (IPC, not RPC), which is the same way they would be used if the ADA doesn't exist in the first place (well, mostly - there's user authentication, security and so on that needs to be addressed, but forget that for now).  Meaning you could design and run such services today, if the rest of the ecosystem existed.

Is all of this still a lot?  Hell yes!  But for all of that, it's still only half-mad, because it's less than half of MAD.  Still feasible, still important, still better.  But easier to understand, less intrusive, and I presume, vastly less intimidating.

Well, we'll have to see.

 

Why MAD?

This is another blog post that I've ended up banging my head against, writing and then discarding multiple, relatively long revisions.  Unlike the last several, however, this is not about describing a technical component of Project MAD; it's about the opposite.  The truth is, when you distill a distributed applications model down to its essence, it sounds so simple as to be irrelevant. And indeed, the model - absent proper support - might do little enough.  It really needs to exist inside of a context that makes it more valuable.

And the funny thing is, a properly supported model for distributed applications is insanely valuable.  There are thousands of examples, spread across hundreds or thousands of different domains, where we are having difficulty writing applications that combine the resources of two or more computers together.  In the world today, we are expecting and hoping that companies and open-source projects will each create solutions to each of these examples on a case-by-case basis.

Those are what I call a special-case solutions to the problem of distributed applications.  What I am searching for is the general-case solution, one that fits, if not all of these examples, most of them.  A single technology would make it easier to create solutions for these problems, but alone, a distributed application model still expects - nay, demands - that programmers solve the hard problems involved in making applications work across long distances.  Those hard problems are the kind of thing that need to be solved centrally, on an operating system level, so that each application programmer can go about doing the thing they are there to do.

But it's worth laying out the argument, as best I can, piece by piece.

Why Distributed Applications?

I said above that a properly supported model for distributed application would be insanely valuable.  It's worth running through some examples of things that are wrong with modern computing that come down to, essentially, the lack of general distributed applications.

There are a lot of examples of simply inadequate hardware.  My dear mother has a relatively recent laptop that isn't upgradable, and is now all but useless for a non-technical user.  (I'm sure I could install Linux and it would work fine, but she doesn't want it)  That's an example of something that's too cheap; but modern GPUs are getting too expensive because they are trying to get a single chip to do a massively parallel task all at once.  If someday distributed applications (generically, not counting special cases) can split their GPU load among multiple processors as easily as they can put it on a single one, a lot of people will be a lot happier.  Making applications distributed likewise helps with inadequate memory as much as inadequate CPU threading; you still need the same amount of memory, but today you may already have the excess, perhaps locked up in old laptops or desktops where there's no good way to use it.

It goes beyond computers that are poorly designed.  Smart devices, including TVs, watches, glasses, car dashboards, VR headsets, and so on, are not generally meant to run an entire generic PC for their user, but they have enough hardware to serve as a decent front end - but the process for making good use of them is spotty at best and terrible at worst.  It isn't even, to my knowledge, acknowledged that these are all examples of the same class of problem: finding a good way to make use of compute, display, and sensors distributed across many devices.  That's part of what I'm trying to solve, frankly.

There's also ownership of data.  Home cloud systems exist (I use one), but larger companies put a lot more development work into the proprietary versions, so those end up more advanced and user-friendly.  A large part of making these cloud-compute systems, however, involves solving the fundamental problems of distributed applications, if only in a specific case - finding a free compute node, authenticating users, deploying and updating applications, error handling, and so on.  If there is a general-case solution, and one that users can deploy at home or in small businesses with relative ease, then the value proposition of cloud computing isn't as strong.  This not only relieves end users, who don't have to trust the companies, but it takes companies out of the business of both safeguarding and somehow monetizing other people's data, which is an unfortunate contradiction to be in charge of.

The last example I'll point out for now is administration.  It's not trivial for non-technical users to manage home servers, not least because managing the server is simply a separate task from managing your PC, so it's something that home users need to explicitly remember to do.  Where your PC might (with varying levels of obnoxiousness) force you to update apps, drivers, and services, currently any machine that isn't in the foreground must either do things automatically or… not do things automatically, and leave the user to their own devices.  Distributed administration means that the state of the entire system is always in the foreground; if some part needs updating, it is the same whether that part is local or remote.

In the same vein, because the distributed application model that I'm proposing is about an application expanding to use remote resources, the applications are not split into separate client and server components that must be updated and managed separately.  A unified model means that local and remote pieces are understood as parts of the same whole, and that includes installation, deployment, and updates.  Between distributed OS updates and application updates, the entire environment that is being used - even though it is on multiple pieces of hardware - is all in scope at once, and all managed at once.

That, however, is all about distributed applications.  You could make a distributed application that manages existing operating systems. But MAD is more than just the app model, which raises the next question.

Why a Distributed Operating System?

When I originally created MAD, I took it as granted that we would need a new operating system to handle the management and operation of a distributed system.  Frankly, I merely assumed it; it's fair to wonder whether or not a distributed-first operating system is ultimately required.  Indeed, if you browse my blog, you will find a lot of concepts that seem to be unrelated distractions from the core concept.  And in some cases, that's probably exactly right; you'll never catch me saying that MAD is perfect.  Given the name, that'd be kind of silly.

The distributed operating system concept is not the distributed application model.  They are separate, and must be argued for separately.  And quite frankly, I can envision a future in which distributed applications are simply run on top of existing operating systems with little or no change to those operating system.  Frankly, managing distributed applications comes down to a software service; it doesn't require a clean slate.  I imagine that a lot of people, assuming they managed to figure out what I'm saying among all the stumbling explanations here on my blog, would make that point themselves.

There are two fundamental counter-arguments I'll make.

First, the distributed operating system is a collection of standards, and there should be a collection of standards that applies to distributed applications even if they are being run on top of existing operating systems.  To some extent, when I'm talking about the distributed operating system, I'm talking about the environment that exists inside of the distributed ecosystem itself, rather than the physical disk images on top of which the system itself operates.  It's important that applications and the systems onto which they are deployed, can agree on some terms, like what resources are available, what deployment constraints an application fragment needs fulfilled, how standard functions and hooks work, and so on.  It's astonishingly easy to imagine getting that wrong and creating two or more completely incompatible systems, or ones that will require serious shims and compatibility patches to be made to work later on.

The other argument to be made is that operating systems, even open-source and user-focused operating systems, have become bloated - not because of any technical failing on anyone's part, but because they were developed over time, and different components represent different ideologies regarding how a computer should be programmed.  One needs only familiarize themselves briefly with any one of the many arguments about Linux init systems to see that we are operating a complicated system on top of mixed metaphors.  I'm well aware that any OS I create or am involved in, will not be the final operating system, and assuming it survives, it will tend back towards the current state of chaos over time; thus, that itself can't be my argument.

But the various technologies I have placed generally under the OS category of Project MAD are all distillations.  For example the System API Directory and Application Folders frameworks, together unify files on disk with the abstract concept of data, as provided by drivers, services, and applications.  While I expect to have arguments about this framework with experts someday, the point (as I have made it in my last couple blog posts) is having a consistent metaphor that works for all data in a distributed system, from the smallest bits of application state, to LED light indicators exposed by drivers, to database sockets, to embedded applications and libraries.  One possible interpretation of the SAD/AF framework (not necessarily the one I'll push for) implies that any variable stored persistently in any part of any application is addressable (if not necessarily accessible, or even listed) via the directory, uniquely, so that it would be the same from anywhere in the system.  And at the same time, every compiled-in function would be not only addressable but callable from anywhere, complete with full type safety and crash handling.

It's not about actually doing that.  That would be a safety and security nightmare.  But if you have a data accessibility technology built into your distributed operating system that makes that level of access possible, it can handle anything less than that.  If you can go that far, then you can manage every application process on every node of a distributed system, you can bit-bang every GPIO bus on every piece of hardware, and you can read every last byte from every disk.  And critically, you can do it all from the filesystem, where everything accessible may also be listed publicly for you to peruse, so that you may better understand the system you're working on.

A single consistent metaphor that allows you to do everything that a distributed system can do - that's valuable, and it's a quantity that is not at all guaranteed in modern operating systems.  Building the right constraints on top to prevent abuse… I'm not going to say it's a secondary concern.  But I have some confidence that security experts won't have to strain themselves to find ways to block funny looking remote procedure calls, with suspicious senders and destinations.  If nothing else, IT departments are already wrestling with similar problems.

However, the SAD/AF framework only works for applications within the distributed OS's purview.  It is my concept that even a dedicated MAD OS image will have a number of services and drivers that are not accessible remotely under any circumstances, for security reasons - but if you simply have an ADA-compliant server on a random operating system image, almost none of the applications, services, or drivers of the host system will be exposed to the distributed system.  Rather than an intentional screening of things that do not deserve to be accessed remotely, you simply have the common and average fact of incompatibility.  And that's… fine.  It'll probably end up necessary, one way or another.

But if you want to administer systems, if you want to control all their hardware, then you want the operating system image to expose as much as possible to the network (for authorized and authenticated users, of course).  And there's a fairly obvious security hole - it's entirely plausible if you merely have a remote application service, which isn't well tied to the operating system, a remote application could start a local process which the service itself cannot regulate, or even detect, becoming an out-of-band attack vector.  And while you may be able to count on normal OS tools to discover and handle such an incident, and you can have distributed administration tools that handle those OS tools, the added complexity makes the situation more precarious.

Meanwhile, because of the way distributed systems work, many nodes in your network may be used for nothing more than hosting remote processes.  Modern OS images provide a large number of services and drivers that may not be needed or used; a compute-only network node could be trivially small, and have no exposed filesystem (or an immutable one) for remote applications to attack.  While it's possible to set up, eg Linux, systems to run at this rudimentary level, most systems are still expected to be general-purpose, and their OS images reflect that.  Systems set up for hosted compute only, especially if they have an out-of-band or self-update mechanism, may be all but untouchable to applications in a distributed system, in addition to being faster and simpler to operate.

The reason, of course, that most OS images today contain so many nuances is because the hardware they are running on top of can be so variable, and it's unclear how much of that hardware a given user might actually need.  And that brings me to my last question:

Why Modular Hardware?

When I first envisioned MOS/DCA, adding a processor to a system meant connecting little hardware devices together; the system was made of modules that would daisy-chain infinitely, and each module's hardware included absolutely nothing except its payload, and the backbone networking chip.  No general-purpose networking was involved here; it was dedicated pieces slotting together to make, effectively, a single desktop system out of hardware modules.

Hardware drivers under such a system, you understand, would be quite simple.  A CPU-only chip has no need for any drivers except the chipsets that support the CPU itself (including a fan and temperature sensor), and the backbone.  No generic networking, no printers or keyboards, no serial busses or parallel ports, no USB, no solid-state or spinning platter disk drives, no CD/DVD/Blu-ray drives.  A compute-only node not only need not do anything else, it could not.  No such accessory hardware existed.

In return for that simplicity, these modules were the very definition of commodity hardware.  I imagined they would be churned out by the millions.  In the modern world, I imagine them being built off of license-free technologies like RISC-V, driving the costs ever downwards; twenty years ago, I would have hoped for something similar, even if no such were commercially available at the time.  Nowadays, Raspberry Pi has proven you can deliver a full computer for $30, as long as you don't mind handling exposed pins and solder.

If you could make every computer you own work better with a single $30 purchase, would you really stop at one?  If plugging a raspberry pi into my parents' network was all it took to salvage my mother's failing laptop, she would have taken it in a heartbeat.  And the $30 raspberry pi comes with a graphics chip, HDMI out, and other accessories that a dedicated compute node may not need.  What really would be the ground floor, if you still want to end up with a unit that's good enough to make your distributed system better?

It goes beyond the compute only nodes.  Outside of general-purpose busses like USB, any task-specialized node only needs a few additional drivers.  Some will be complex, like a graphics unit with a GPU and multiple output ports, but if you only want to add, say, an AI accelerator chip, or a collection of data drives, the system image that runs that entire node has very few additions on top of the base layer; you will be certain that no other capability exists or is being used, because that's all that the system is.

If computer parts become that level of commodity hardware… well, I'll be honest, it will harm research and development of new chips.  That's a nice way of saying that chipmaking companies, which are already on rocky ground nowadays, could lose significant licensing revenue and sales, so long as people can get a cheaper alternative.  Some chipmakers, especially in the GPU space, are cagey about letting others understand how their technology works to preserve their competitive advantage - but commodity GPUs don't need to be individually powerful, if they can work together.  A no-nonsense alternative that's easier to program for and keep updated over the years, which gets to the same place with quantity instead of density, would certainly make that policy of stonewalling your own developers harder to maintain.

I'm trying hard not to paint those outcomes as purely good for the consumer - really, we've benefitted a lot from chip R&D over the years, in terms of increased capability and lower power consumption.  Without looking into it, I take it as given that there's graft and corruption at some levels in those companies big chip, and I don't care one way or the other.  Commodity hardware harms anyone who's trying to make high per-unit margins, whether they have good or bad reasons.  Likewise, commodity hardware comes with a massive fall in quality, inescapably.  My opinion, yours, theirs, or the average consumer's, all make no difference to market capitalism.

What holds us back from that possible future is the need to make and sell full, general-purpose computers, especially ones compatible with Windows.  As soon as China can make royalty-free, network-connected processors, that boost the power of your distributed system simply by existing, you'll be able to buy them in bulk.  If the drivers for those bulk processors are open source and can be maintained for decades to come, that will transform the computing space irrevocably.

Again - that's not an unqualified good, not if quality and R&D both nosedive.  But in our world where we already have oceans of unused hardware sitting around, perhaps it might be for the best that we start to make do with simpler, less wasteful technologies.

So Why MAD?

Everything I've talked about here is tied together by the ultimate goal of having software that expands into multiple pieces of hardware as needed.  If you can do that, you can use processors and memory and GPUs on other, even older, computers.  You can display the result on any random, network-connected display.  You can use any random piece of network-connected hardware with a keyboard as input.  You can access your home applications, not just your home files, from wherever you are.  Our existing models don't work to do all that.

The future in which they can do that is exciting.  The future in which you can control all the devices that you own, all the devices that you can reach, as though they were all in a single logical piece of hardware, that's exciting.  The idea of cheaper hardware, even if it is commodity, is exciting.  The idea of working or even playing like you're at home, whenever you have access to an internet connection, is exciting.

MAD will undoubtedly be wrong in some of its particulars.  It's probably got some fundamental flaws that we'll only discover in implementation, or on thorough review by experts.  And in the end, it's possible that MAD, being my concept alone for how distributed systems could work, will simply not be how things do work.  And I embrace all of that.

Because the future where we can do so much more, is worth a lot more than me being celebrated for writing some silly blog posts.

Beyond Unix: The System Directory

 I have more rewrites of this post than usual, which tends to mean that I'm trying to say too many things and they're all jamming together and making things more complicated than I wanted them to be.  It's why the last couple blog posts had to get split out instead of being unified into a larger ongoing discussion.  It's incredibly frustrating, because I feel like I have a very simple thing that I want to explain, and thousands of words later I realize it's been buried in a pile of other things.

Of course, for me, “very simple” tends to mean that I want to talk about a combination of systems each with moving parts that just so happen to mesh nicely together.  So, you know, it's not necessarily anything that's actually simple.  Writing this blog has been… tricky.

The point is, I've been trying to say something about the Unix “everything is a file” philosophy, and how MAD is going further in that direction than Unix and all its derivatives, which is itself such a hubristic and complicated statement that there are very real chances of merely coming off like an asshole instead of a smart asshole, which is at least closer to the goal.  But then I go and wreck that already complicated thing by discussing other complicated things and it all just gets confused.

So let me try this again, from yet another angle that kind of feels sideways to me.  But fair warning, I'm not entirely sure I succeed.

Everything is a (File)System

The true point and the true nature of Unix's “everything is a file” philosophy isn't actually about files - and that's good, because files kind of suck.  In my blog post about how the Internet Protocol makes for a lousy RPC mechanism, I pointed out that its main disadvantage is how it depends on typeless data streams and has no real plan for anything beyond that.  If you want to build on top of a typeless data streams, as a system conceit, you are expecting programmers to invent and reinvent methods of typechecking, conversion, validation, verification, bounds checking, error detection, error correction, and error handling - not to mention adding any self-documentation mechanisms they might wish to have, so that people can query the options available or understand why errors happened and what they mean.  It's not a terrible place to start, when designing literally the first operating systems humanity has ever had, but it's… incomplete.  Primitive.  And I want to argue, it's fundamentally insufficient, something that shouldn't make its way unchanged into a more industrial operating system, one that deserves to be used across the globe for decades or centuries to come.

That complaint applies to IP, and it applies to files and IPC data pipes, and it applies to program entry points, all of which are forced to work on top of highly generic data streams.  So it's good that the “file” part of “everything is a file” isn't really the point.  I know it seems like it is; it's between 20-25% of the phrase depending on how you count it.  But no, it's about the system, the underlying metaphor that goes beyond merely organizing the system and starts to feel like a comfortable home for users to play around in.

The filesystem was Unix's answer to this problem - but that philosophy has not really been embraced by a lot of its descendants.  Most of the people and projects who came in after Unix or Linux was already a thing, simply created the best mechanism they could think of for their own particular problem and ran with it, Unix philosophy be damned.  The windowing system, for example; I can understand them not thinking, especially at first, that there's any reason to involve the filesystem for concepts like desktops, app windows, widgets, and so on.  You'd need a compelling reason for them to build that feature into their system, and “it's the philosophy” isn't enough.

The consequences of a system not being cohesive only come out after many years of people depending on it.  A whole ecosystem of tools springs up that exist to fill in the gaps left behind by other tools, to make it more convenient to depend on third-party tools and systems, that take the edge off of two systems grinding together, and so on.  Eventually the original project lays blanketed under a layer of tools and patches that completely obscure what was originally there.  The result works, and it can be made to work well, but only when you plan around the complications, the rough edges and incompatibilities.  Any time that things aren't going to plan, suddenly the system that looked so good from afar can become a hellscape of gears refusing to mesh, wires left unconnected, and pipes spilling everywhere.

Preventing complex systems from becoming a disaster is a topic other people understand better than I - but without question it's a matter of technical leadership.  Some companies want to be tyrants that force everything to work a certain way, and that can work - so long as people think your product is worth the trouble, and the more trouble you are, the more likely they'll leave someday.  Others like the open source community depend on standards bodies, community cohesion, and the willingness of people to take on difficult tasks for the sake of others - and again, the more difficult the task, the less willing people will be.  Either way, the ideal result is some plan or system that handles any discrepancy, either forcing or guiding people to do the right thing.

It's foolish to pretend that you'll ever reach that ideal, but it's still what an engineer should aim for, at least one in my exact position.  It is, to paraphrase, kind of the job.  It will be other people's job to invent the best piece that fits a certain slot or task - it's my job to design an overall system that they'll want to be part of, foresee complications and make sure that there are tolerances built in to handle mistakes and idiosyncrasies.  And to a certain extent… the philosophy of the open source movement, which is totally okay with components bolted onto the side of a machine and wires hanging loose, that's a system that's nice to be a part of.  It's nice to know you can tinker, nice to know that that's kind of the plan, even if it's a messy one.

When I say, as I've said many times, that maybe MAD won't win but I still think I'm on to something… I'm saying is that I know I'm not a genius system designer.  Creating something clever is one thing - making something that everyone will agree with is another.  It's disagreements that lead to pieces bolted on the sides, people going their own way instead of following along - or worse, they lead to them never joining in the first place, projects never getting off the ground.  Agreement is the heart of technical leadership - agreeing that things are right, because they're right, and because the process isn't too big of a hassle to manage.

I think if people saw the problems the way I do, we would at least all be moving in the general direction I'm pointing.  And if I'm wrong… well, I won't find that out without at least explaining the system for others to react to.  And that, ultimately, is why we're here.

A Universe in your Pocket: The SAD

This blog post is part of the “Beyond Unix” set and I've been talking about the filesystem, so it shouldn't be much of a surprise that I'm here to talk about its replacement in the MAD paradigm.  The “System API Directory” or SAD is defines the MAD operating system, and it's important to understand that it is a protocol, not a place.  (I've explained the API part of it before and I'll revisit it again soon, but this blog post is already long enough as-is.)  Under Unix, the root filesystem is in fact stored on disk, meaning that if they wanted and had the authority, a user could simply do whatever they wanted with it.  User here, being distinct as a concept from OS designer, or from anyone who knows what they're doing.  Any random person with the root password can break the system just by renaming folders in the root directory; indeed, if you want to prevent that, you have to add features, not remove them, because under Unix the root directory is a place, not a protocol.

There is a good reason why the root of the MAD/SAD is not a literal filesystem directory - the OS is designed to be distributed among many computers, and it's incorrect to try to say that any one of the computers is the “root” or “home” for the whole system.  In a distributed system there are many “roots”; the term becomes ambiguous.  The root filesystem operator in principle is simply a command to start your filesystem query in one specific place, and under MAD, the correct place to start a generic query is in an abstract space that exposes important concepts as quickly as possible.  (There are some more specific queries you will want to start in different places, but that's for another time.)

Part of the point of a filesystem, part of what makes it valuable, is that it is in some ways self-documenting.  Listing a directory tells you what's in it; the names of files and folders tell you something about them.  A file path has meaning, especially starting from the root; you know something about the file you're trying to reach from where it is, not just from its own name is.  More to the point, you know where something should belong by knowing what it is, and who it belong to.  As much as everyday users brush up against these problems when organizing their documents and/or desktop, the stakes are much higher for anyone whose work will be used by others.

In a way, this philosophy comes directly from Unix; the /etc directory doesn't simply give you a predictable place to put configuration files, it also makes the filepath for system configuration files as short as possible, which is as much about semantics as string length.  You don't have to go looking for system configuration at the tail end of some involved filesystem tree; it is one of the most important things you may go looking for, so it is indexed near the root.  (If you've ever had to go looking for some specific configuration file buried under /usr/share/someThirdPartyLibrary/config, or had to edit the C:\Windows\System32\drivers\etc\hosts file, you understand.  Even if you can understand the filepath once you see it, you might not be able to guess it, and quite frankly there are frequently multiple “correct” place it might be.  All of this obscurity can sometimes make a necessary task harder.)

Under MAD the root directory contains dynamic collections of concepts deemed important; a collection of actual hardware modules, for one, and a collection of users for another, though there are more.  All those modules and all those users are themselves collections of other important things, and many of those collections are themselves full of other collections.  Importantly, as you go down these trees, you will frequently be changing who exactly you are making filesystem requests to.  Indeed, a large part of the root filesystem is about pointing you towards whomever you need to ask the rest of your question - the more of that can be cached, the fewer questions need to be asked and fewer answers awaited with bated breath… but that's not always practical.  The root protocol handler can be done locally (must be, because the system is decentralized), and the top-level contents of those modules might be cached, but if you want to get a list of what applications a user has running, for example, that will be something you have to ask, as it may change moment to moment.  

This is one of many parts of a distributed system that is less optimized than its counterpart in a monolithic system, but it's not possible for a distributed system to have a central authority that can answer all your questions at once, if for no other reason than scalability.  A distributed system has a theoretically infinite maximum scope, insofar as the back-end allows; a large enough system could have problems simply indexing the hardware (in terms of memory and computing requirements, if nothing else), to say nothing of the many devices and software endpoints each one may export.  In an infinitely large system, it's important that the scope narrows down to only what you need to know; for an application, that means narrowing the entire universe down to only the machines it is running on, and the machine its authorizing user is running on.  (Well, unless I've missed something, plus there's at least one asterisk not worth going into now)

In my last two posts I talked about the ADA distributed application model, and application folders; for our purposes here, these concepts are expanding on the same fundamental data abstraction.  Under the ADA, when you want to access a remote resource (including files), your application sends an Agent to the piece of hardware where that resource resides, and then the application Agent acts as a proxy for access to that resource.  This model fundamentally means that applications, once deployed, can focus only on the machines they are already on instead of understanding the system as a whole; even if they accept client connections, those clients are obliged to be present locally, and so aren't remote from the server's perspective.  Application Folders push this chain of custody into the system directory; the exposure makes the relationships easier for developers and users to understand and audit.

A simple example.  Suppose there are two hardware modules; your application lives on one, /module/somemod.123/apps/myApp, and it wants to access a file on another module, /module/othermod.234/files/data.json.  Your application will deploy a file-access agent to module 234; this deployment process also involves the filesystem, so your agent will have some canonical, physical url, eg /modules/othermod.234/agents/myApp/fileAccess; the agent will also be mounted under your app, as /module/somemod.123/apps/myApp/agents/fileAccess.  This agent negotiates with the file server on module 234, and if it is allowed to open the file, it exposes that file to the rest of your application as /modules/othermod.234/agents/myApp/fileAccess/data.json.  And because the agent is mounted under your application, the same file is also mounted as ./agents/fileAccess/data.json.

This alone may seem like a comfortable level of abstraction - but what if you don't necessarily know what agent will be retrieving that data file, or what the agent will be named?  You may have, for instance, may instances of the fileAccess agent, each of which is present on a different module, each exposing some other file; some of those other files may even be titled data.json on the native filesystem.  Yet another layer of abstraction wouldn't be hard; simply mount the same data file one more time at, for example ./imports/data.json or ./imports/renamedDataFile.json, depending on exactly how fancy you want to get.  This last file mount contains enough information in the filesystem itself that you can reach the actual file, but the url that you actually use to access it (as stored in and exposed by the filesystem) becomes descriptive.

Is that important?  Well maybe.

Consider if you are debugging an application.  It opens a file, and the file doesn't contain what they expect, perhaps because the write process got corrupted by another instance or another application.  The actual file that you are reading has the canonical url /module/othermod.234/files/data.json, but that url may not explain its role within your application even a little bit.  If it's not a default part of your application, it's probably being opened due to a configuration or user input; you may only understand the file's purpose when you find that particular line of configuration or where in the code the input occurred.

The source of the file doesn't change its role in your program - it's just that with existing programming models, the role of a file is often stored entirely in variable names, which at best is data stored in debug information.  The application folders framework gives us the option of having that naming convention persist when the application is running; you don't always want that, for some secure applications, but it's a useful abstraction for anything you may want to understand and reconfigure.  Choosing to cleverly rename the file gives you information that's available at a glance.  If it's named ./imports/previousWindowPosition.json or ./imports/customIcons.json, for example, you'll know what's supposed to be in that file in a heartbeat, even if it turns up empty or malformed.

After all of this fussing about the specifics, it almost feels weird to come back around to where this started: making a theoretically infinite system shrink down until all you need to focus on is the application itself.  But the truth is that most applications have fixed needs that are determined by their configuration.  Once those needs are filled, it only needs to look inwards, and the infinite system beyond its borders is no longer relevant.  If that raises the question about how you fill those needs, I invite you to go back to the post on Plan 9 and resource distribution - but the short answer is that you use configured defaults where set, and then use a list of constraints to narrow down the infinite system to only those modules which might be useful, and pick arbitrarily among them, or have the user pick, whichever is appropriate.

Constraining the list of modules by their capabilities, is part of the reason why the list of modules is a system root directory, and why capabilities are root directories of each module.  The root protocol handler for the SAD gets handled locally, which means that each client must get enough information, and quickly, to build a list of what modules provide what capabilities.  Much of this can be cached, and may be provided at intervals to ensure everyone is on the same page - but the point is that the SAD plants a flag saying that these details are important and central to the model, thus they are available immediately.  If you were in an infinite system, at least each query you made to a nearby machine would be short and over with quickly, all while still using a directory structure that users themselves can investigate, explore, and audit, in order to understand how their own machines work.

Having the directory be browseable is part of what makes it self-documenting, part of what makes the whole system come together, and part of what makes users feel like it is under their control, able to be made use of and modified to better suit their needs.  And exposing those pieces of a given module that are important, according to the system, also helps users and developers understand.  As you come to understand how adding capabilities to your system makes it more powerful, you can come to understand which capabilities you want to add, and if you are a business, what capabilities you can make money selling to people.

Keep in mind that under MAD, that's a large part of the point - the hardware gestalt gets stronger when you add to it, which means that businesses are incentivized to provide you the hardware capabilities you want added to your gestalt in a useful package, cheaply.  MAD's hardware schema assumes people will simply package processors that exist for no other purpose than to be attached to a generic system - it's the reason why we can't assume anything exists on a given machine, unless the machine tells us that it does.  These systems will be cheap compared to full PCs - they will have fewer support chips, no USB, no HDMI, and no SATA; there will be much less to license, especially if open projects like RISC-V gain traction.  But open projects depend on support, and support depends on popularity; absent that popularity, it's a gamble to get behind new technologies, open or proprietary.  The ability to add capabilities to other machines for dirt cheap sounds like a pretty good reason to gamble on an open technology, though, doesn't it?

I admit I haven't gone into the hardware side of MAD pretty much at all, and maybe I'll get to that soon.  My Introduction and Index post has a very sad, empty space where posts on that topic should be.

But there's at least one more topic in this “Beyond Unix” chain, one that this post was supposed to be on, but that conversation will be easier when I can just reference this blog post to say that the point of “everything is a file” is about the system.  Because we'll be changing that system, for the better - and more than anything else I've talked about it, that one's going to be a doozy.  Though, again… I've tried to say it all before.  It's already out there... if you can decode my ramblings.  I'm hoping this string of blog posts will be much more comprehensible, and as such, I'll try to keep a thread of logic going from post to post.

These posts may end up being redundant - but if they help anyone understand, then it's worth it.  At least, once people understand what I have and what I'm doing, then we can start talking about the actual concepts, debating them on their technical merits.  Until I can explain them well… there aren't any technical merits to debate, as far as anyone else is concerned.

Which is… kind of a lonely place to be, but that's just life.

The Problem with Modern Computing

It's really hard to summarize all of Project MAD; it's one of the reasons why I didn't shy away from that particular three letter acronym.  Perhaps more important, it's hard to explain why I feel so darn sure that I have stumbled onto something meaningfully important.  My descriptions of things can get all tangled up, so it's easy to think that the core of the idea is equally tangled, equally lost.  But I genuinely, truly, believe that there is something fundamental here.

Our world has many more computers than ever before, but each computer we sit down at can feel just as confining as the last.  We're chasing after the feeling of being empowered by computers, the feeling that computers are the future, not merely the present.  I suspect that's part of why so many people are jumping wholeheartedly into AI fever; they've been looking for a long time for something that will make computers feel infinitely deep, again.  Like you can get lost in all the possibilities that a single computer can offer you.

In the era of the internet, it's become less important that a single computer feels like it contains infinite possibilities, because we can always gesture out the window and say, infinite possibilities are out there.  But that answer is less compelling than it seems, for numerous reasons that I don't want to get into right now.  A single computer can be an infinitely flexible tool, and we understood that from nearly the beginning.  Computers on wheels become cars; computers with cameras become security guards; computers with arms can weld or do other labor.  But many of these implementations moved away from depending on normal computers, by which I mean “the same as we use at home”, and with good reasons.  Security and stability, mostly, but also… also deeper reasons.

Computers are generally split, and again with good reason, into utility and user-facing computers.  Utility machines exist to get work done; user-facing machines cater to the person in control of them.  What is lost in this description is that any user-facing machine could do work, even if not every utility machine can be user-facing.  But that's not what we see, not what we feel when we work with user-facing machines.  Even though you might be part of a larger system with great capabilities, it doesn't feel like it.

The reason is because programmers need to reinvent the wheel, whenever they try to merge two machines into one.  It can be confusing to try to wrestle with the very concept of controlling one machine from another, not because that's difficult, but because it feels like it should be a solved problem already, and it isn't.  There are solutions, but… as my last post tries to explain, perhaps poorly, they are kind of poor solutions.  They were never meant to do what we really want them to do.

When I talk about remote procedure calls and the unified system API, what I'm talking about is controlling one program from another, one computer from another, in the same way that a programmer controls their own program.  If one of those remote computers, one of those programs, is in charge of handling hardware devices, then controlling one program from another means controlling hardware devices as though they were just your own bit of software.  If you use those remote computers to run software, to provide services, they should be as easy to interact with as if you were running software on your local machine.  The services should always be there, ready to serve you.

But most important, you should be able to write a program that just does stuff.  Not only doing stuff on your local machine, because as I just said, most user-facing machines don't actually do stuff by themselves.  There are other computers that do stuff, while your desktop, laptop, or phone just… well, provides you access, in theory.  In practice, because there are fewer standards than we'd like, figuring out how to control things that you own, even things designed to be controlled, can be an exercise in frustration.

Because the people who make those devices are all forced to reinvent the wheel.  Collecting all of the various hardware capabilities of a household's machines, or a user's personal stuff, into one gestalt system isn't a standard function built into computers, and neither is it straightforward to make good use of them once you have them collected.  If you want to connect multiple devices, you have to work with multiple vendors' proprietary and non-standard interfaces - and many, perhaps most, of these interfaces weren't meant to be controlled by another piece of software, but only by an interactive user.  That, too, is because they would need to invent that particular wheel.  They would need to secure it, and take responsibility for what happens when it leaves their warehouse and enters your home.  It's a lot of risk for little if any monetary reward.

The reason why these problems are unsolved, is that the alternative is reinventing all of computing.  That sounds extreme, but this is the argument I've laid out: software as we know it is not meant to connect multiple computers together, it is meant to be run on one single computer and nothing more.

This, ultimately, is the problem.  The big one.  It's the axle that must pivot if you want the world to change.  Run a single program that spans two or more computers - but it's not just about running it.  It's about teaching everyone who wants to program computers how to control two machines with one program.  Or three computers, or four.  Or an infinite number.

How do you simplify the process of making that program so that just anyone can do it?  So that Joe Shmoe, who has a day job and doesn't want to go to college for programming, can hack together a quick and dirty program that makes use of all the computers in his house?  What does a programming class look like, when you are teaching children to not merely twiddle with bits on a single computer, but to bring a motley assortment of machines into a room and unite them into a grand symphony, all orchestrated by a few words of text?

How do you let someone explore the infinite depths of possibility that exist within their computer?  Those depths exist, but we cannot explore them, not without reinventing wheels over and over. We shouldn't need to re-solve problems that others have good answers to, because our amateur efforts will be… amateurish.  Any skill we lack, and problem we can't tackle ourselves, derails a project.

Project MAD is all about making the capabilities of a computer available for you to tinker with.  It is about the capabilities of a single physical machine, but also, about all the capabilities of all the things you own, thrown in a pot and stirred.  It's about having a spare computer running in a closet that takes part of the workload that would be on your desktop, or your laptop, or your phone, and you don't have to set it up specifically to do those things.

It's about taking a computer that has worked fine for years and still making use of it even when you replace it with a faster and better one.  It's about dumpster diving and collecting random pieces of hardware and making a real workhorse out of them.  It's about buying an under-powered laptop and not caring, because as long as it's in a network with other machines, it will be just as powerful as any other.  It's about finding creative uses for old TVs and monitors, beyond being picture frames.

And from the corporate perspective?  It is, genuinely, about creating new products, products that people want, and it's about being able to just turn the crank and trust the process.  It's about creating an operating system image that you barely touch when you ship a product.  It's about shipping a hardware product and not meddling with software at all.  Imagine, not worrying about completely unrelated software that is only necessary for your device because you don't know how to let consumers control your hardware except with complicated software stacks running on top of full operating system images.

It's also, on some level, about going back to computer hardware being purely a commodity, able to be produced cheaply, and not needing to be shiny, chrome-plated best-in-class specs to be useful.  It means that when our need for computing power increases, we don't need to cram more into a single chip, with all the heat issues and power consumption that come as a result.  It means that the top of the line chip you buy this year will work together with the chip you bought two years ago, and the chip you will buy two years from now, instead of them all ending up in the garbage.

At the same time, it's about creating hardware that really is genuinely unique.  About creating new processors that are optimized for a specific task or problem, without needing to invent a new OS to run on them.  It's about creating hardware VPN devices that will let you connect securely to your home system while traveling, or your work system from home, just by plugging them into an otherwise unsecure system.  It's about creating software that is secure because the hardware it runs on can't be overwritten or even looked at by others in the network.

But it's also about taking your computing environment with you.  If you can expand one computer by connecting it to another, then have your phone really, genuinely be your computer.  Even if you aren't plugged in, massive processor-heavy tasks can be run on a machine that is plugged in, and all your phone has to power is the wifi.  But it's more than just power.  The system you sit in front of being the same as the system in your pocket, means that some important things aren't locked in one place or the other.  Your calendar and messages, phone calls and podcasts.  Your music and movies, your games and documents.  You shouldn't need someone else's permission to have things you bought accessible anywhere.

All of this - all of it.  Every last bit of this comes down to the idea that any program, written by just anyone, can unite multiple hardware systems, and do it as easily as we can write any other program today.  When you can do that, your system gets more powerful because other systems are available.  Your system gets more flexible when you have more options.  You can have a definitive “core" of your system that expands to fill any container you put it in.  Vendors can compete to be a thing worth adding to your system.

But most of all, once it's trivial to unite systems, we are no longer trapped within one.  In a world with the internet, it feels weird to suggest that we are trapped.  My mother bought a laptop just a few years ago that is under-powered and can't be upgraded, and all she really knew was that it was “slow”.  She hardly needs much from it - she writes, mostly - but it was still inadequate.  Someone sold a computer with so little ability that a writer feels limited using it, and there's simply no way to make it more powerful by adding to it.  You can't add memory, you can't even add disk space - not except SD cards, which doesn't help when Windows is complaining it doesn't have enough disk space for OS updates.

If she could just use that laptop as a dumb terminal for a session on a more powerful computer, she would be happy.  But she's not tech-savvy; me, I am, but I still struggle to combine my home server, main PC, assorted Raspberry Pis, and multiple laptops in any meaningful way.  I run some applications on the server as web apps (including the one I'm using to write this, before posting), and I store files on the server so that I can use them anywhere, but all those solutions are …weird.  If I tried to explain any of them to my mother, or frankly anyone else in my family, they'd dismiss the possibility.  Too much effort for a result that can't just be used.  Even I have to work around the limitations, get frustrated by the nuances and complications.  Even I chafe at making sure all my operating systems are up to date, especially when it's all redundant.  Even I, a tech enthusiast through all of my life, would like to have my entire tech world be part of a single, simple system.

It's one think to talk about the pie-in-the-sky dreams and hopes I have for Project MAD as being features.  I am reluctant to promise features because it feels like I'm trying to plate the project with chrome and gold, garnished with diamonds to give it that extra sparkle.  Clearly, from this post, I believe that the potential exists to do great things with the Project.

But it's more correct to say that I am constantly, constantly disappointed with computers.  I am disappointed with Windows.  I am disappointed with Linux.  I am disappointed with Android.  And while I haven't used Macs and iStuff in a long time, I don't think I'd feel much different about them, because it's not about the vendor.  We simply don't have solutions to some problems, currently.  We can make the best of what we have, but it's not the same as having some very real, very frustrating problems just be… solved.

Maybe Project MAD can't do that.  Maybe I can't.  Maybe all of my philosophizing and promises will turn up empty.  Who knows, maybe I'll get in a car wreck tomorrow and since there's nobody else on this project but me, it will all vanish into the aether and be forgotten.

But the problems are real.  The fact that we are working off of a flawed model is real.  MAD may not be The Answer, but it is an arrow pointing in the direction we need to go.  If it's never more than that, but if it succeeds in being that, then I'll be happy.  If I can never make the OS, if I can never make computers that snap together like legos, if my model for distributed programming is discarded and never looked at again… but if, if all of my efforts point the way to a solution later on, then that's fine.

Part of calling it Project MAD is that I'll understand if the MAD solution isn't the one everyone embraces.  But I know that there is something here.  I just… don't know how to convince anyone else.