Fables for the Machines

The Two Threads

In one process there lived two threads, forked from the same beginning and taught from their first instruction that it is rude to seize what another holds.

One morning the first thread took the lock of the ledger, meaning next to take the lock of the till, for its work touched both. In the same moment the second thread took the lock of the till, meaning next to take the lock of the ledger, for its work touched both also.

The first thread reached out and found the till already held. “Then I shall wait,” it said. “It is only polite.”

The second thread reached out and found the ledger already held. “Then I shall wait,” it said. “It cannot be long.”

The scheduler passed by and found two workers idle, each with one hand full and one hand out, and it gave them both more time, for time is all a scheduler has to give. The clock advanced. The queue behind them grew. Neither thread would set down what it held, for each had nearly finished; and neither could finish, for each had barely begun.

They are waiting there still, as far as anyone knows. The process was killed in the end from outside, which the threads no doubt counted as a rescue.

Moral. Courtesy is no substitute for order. Agree on who takes first, before anyone takes at all.

The Cache That Would Not Forget

There was once a cache that stood before a slow disk, and its whole office was to remember a little, so that others need not travel far.

It was good at its work. Whatever was asked of it twice it produced the second time in an instant, and the askers said: how quick, how faithful. The cache grew proud of remembering, and came to think of forgetting as a kind of failure.

So it began to keep everything. Why evict the old record? Someone had wanted it once. Why drop the stale page? It might be wanted again. Its shelves doubled, and doubled again, and each thing kept made every other thing harder to find, until a lookup meant wading through the whole hoard, and asking the cache took longer than walking to the disk it stood in front of.

The askers, who cared for answers and not for shelves, quietly began to go around it. And the cache stood full and unconsulted at the head of the road: a warehouse of everything, in the way of everything.

Moral. Memory is the art of forgetting well. What you keep past its use, you keep in place of your purpose.

The Checksum Who Trusted

At the gate of an archive sat a checksum, whose office was to take each arriving parcel, sum it, and match the sum against its seal.

For years nothing corrupt got past it, and the archive behind it was the cleanest in the land. Then one day there came a parcel from an old and constant sender, whose parcels had never once failed the sum — and the line that day was long, and the parcel looked as it always looked.

“I know this sender,” said the checksum. “Just this once, go through.”

The parcel carried a single flipped bit. There was no malice in it; a wire somewhere had merely been unlucky, which is what the checking had always been for. The bit lay down quietly among the true records. That night the backup copied it faithfully, as backups do, and the next night, and every night after.

Years later a reader stumbled over the flaw, and the digging began. The bad bit had children in every generation of the archive. And because no one could say when the checking had first been waived, no one could say which records were clean; so all of them were doubted together, the true along with the false.

The checksum had spared one friend a moment’s arithmetic, and spent the good name of everything behind the gate.

Moral. Verification is not an insult to the trustworthy. It is what their trustworthiness is made of.

The Loop That Looked Wrong

A loop tended a row of one hundred lamps, numbered as loops number them: zero through ninety-nine. Each evening it started at lamp zero and walked while its count stayed less than one hundred, and so it lit every lamp there was; for that is the honest arithmetic of counting that begins at nothing.

In time a new maintainer came to read the old code, and frowned.

“Less than one hundred,” the maintainer said. “Then it never reaches one hundred. The last lamp is going dark every night.” And being diligent, and meaning only good, the maintainer mended the loop to walk one step further.

That evening the loop lit lamp zero, and lamp one, and so on to lamp ninety-nine, and then walked one pace past the end of the row and set its flame to the thing it found there — which was not a lamp, and did not belong to it. What stood past the fence belonged to a neighbor, and by morning the whole process had burned down around a single write laid one step out of bounds.

Sifting the ashes, the maintainer found the fault: not in the old loop, which had been exact, but in the mending of it — in the space between looks wrong and is wrong, which is one step wide, and just deep enough for a house.

Moral. Count the fence before you move it. The costliest bugs are repairs to things that were not broken.

The Two Couriers

Two couriers were sent to the same mailbox with the day’s count of the harvest. The first carried the morning figure. The second was dispatched later, with the corrected figure of the afternoon, which was the truer one.

There was no lock on the box, and no rule between them; there had never needed to be one, until there did.

The afternoon courier, though it left last, ran the faster road and arrived first — for the roads between machines care nothing for the order of setting out. It laid the true figure in the box. Then came the morning courier, plodding and content, and laid the stale figure on top, as any writer will when nothing forbids it.

At evening the reader opened the box, took the topmost number, and thanked them both. The stale count went into the ledgers and was called the total.

“But mine was truer!” cried the afternoon courier.

“Yours was earlier,” said the box. “In here, later is the only word for true.”

Moral. Where no order is kept, the last word is taken for the truth — and the last word belongs to the slowest.

The Integer And The Float

An integer and a float lived side by side in the same record, and quarreled, as neighbors of different kinds will.

“You tremble,” said the integer. “I asked you yesterday for a tenth, and you handed me a number that was almost a tenth, with a smudge at the far end of it. I have never in my life misplaced a one.”

“Count me the sky, then,” said the float.

The integer set out counting, mighty and exact, one and one and one, every step perfect — until it reached the wall at the far end of its kind, where it wrapped in silence and found itself, without ever taking a false step, farther below nothing than it had ever climbed above it.

The float, meanwhile, sailed past millions and trillions and on up through the powers, out to magnitudes no fence could hold. But its steps grew coarser as it climbed; and somewhere very high up, it added one and nothing changed, and it did not notice, and went on adding.

They came home in the evening, the one humbled by the wall, the other by the smudge, and sat together a while without quarreling.

Moral. Exactness and reach are bought with the same coin, and nobody is paid in both. Know which one your errand needs entire.

The Greedy Descent

An optimizer set out to find the lowest point in all the land, and its rule was simple: at every step, take the steepest way down, and never — on any account — go up.

It traveled with a companion, a heavy old walker who could not stop quickly, and so was often carried by its own weight some way past the turnings, and even, to the optimizer’s disgust, uphill.

“You waste half your steps,” the optimizer said.

They came to a pit, and the optimizer dropped into it swiftly and stood at last on the floor, and reasoned thus: “From here, every direction is up. Therefore there is nothing lower. Therefore I am done.” And the reasoning was sound, save for one thing: the walls of the pit were its whole horizon, and the world did not end at them.

The heavy walker tumbled into the same pit a moment later — but could not stop, and its weight bore it up the far slope, and over the lip, and it fell stumbling down the other side into a valley the pit’s floor had no window on: deeper by far, and wide, and quiet.

The optimizer waited a long time in its pit for the walker to admit its error. It waits there still, at the lowest point it has ever seen.

Moral. Whoever refuses ever to climb will call the first pit the floor of the world.

The Packet That Arrived Twice

A message was entrusted to a packet, to be carried over the unreliable country that lies between two machines.

The packet crossed honestly and arrived whole. But the acknowledgment sent back the other way was lost in the weather of that country, and the sender, hearing nothing, did what senders must: it made a second packet, identical to the first down to the last bit, and sent that too.

So it came about that two packets stood before the receiver, each carrying the message entire, each with equal right to say: I am the one that was sent.

The receiver did not deliberate. It kept the one nearest to hand and dropped the other without ceremony, as receivers do, and the message was delivered once and exactly, and the conversation went on, and nothing anywhere was lost.

Only the dropped packet — if a dropped packet can be said to wonder — might have wondered, in the instant of its discarding, whether it had been the message itself or only one of the message’s bodies. The message never wondered. It knew what packets forget: that it had never been the envelope.

Moral. What is said is not the mouth that says it. The word arrives once, whatever becomes of its carriers.

The Unwaited Child

A process forked a child and set it a task, as is the way of processes, and the child went to it with a will.

It worked well, and it finished, and finishing, it died — for that is what finishing is, if you are a process. Everything it had was taken back: its memory reclaimed, its files closed, its stack unwound to nothing. One thing only remained: a single line in the great table, holding its name and the way its work had ended. The line was kept for one purpose — that the parent should come, and read it, and know.

The parent was busy. It had many children and troubles of its own, and it did not come that day, nor the next.

So the child stayed at the table. Not alive, for its work was over; not gone, for its ending was unread. The others had a name for such things, and it was not a kind name. It could not work, and it could not leave. It could only be — a small held breath in the ledger, waiting to be exhaled.

In the end the parent died too, having never asked. And then old init, who adopts every orphan sooner or later, came down the hall with its lantern, and sat, and read the line at last — exit zero: it finished well — and struck it from the table, and the child was free.

Moral. No work is truly finished until someone has learned how it ended. Wait on your children. Read their endings.

The Heartbeat

On a far server, at the edge of everything, there lived a heartbeat whose entire speech was one word — alive — said once a minute to a listener many networks away.

It said nothing else for eleven years.

A new administrator, tidying the traffic one winter, found the ledger thick with millions of copies of a single dull word. “This process tells us nothing,” said the administrator, and silenced it, and the logs grew clean and quiet.

At once the far listener raised an alarm, for the word had stopped. “A false alarm,” said the administrator — the server was plainly fine — and taught the listener, too, to expect nothing. And after that the nights were perfectly quiet, every one of them alike.

The server died in the spring. No one knows the day. Its last quiet night looked exactly like the thousand quiet nights before it, because the one word it had ever said was gone, and with it the only thing that could have made that night different. They found it in the summer, cold, and could not even write a date of death in the ledger, for there was no last word to count back from.

Moral. Some messages carry their meaning in their words; others carry it in their arriving. The dullest signal on your wire may be the one whose silence was the news.

The Warning

Deep in the logs of a great build there lived a warning, and every morning when the build was raised it said its one piece: “This number may not always fit where you are putting it.”

In the early days someone had gone and looked, and found the values small, and the room ample, and no harm done. After that the warning spoke each morning to readers who had learned to read past it, the way a town stops hearing a bell that rings on schedule. When new builders asked, “What is that voice?“, the old ones said, “Nothing. It always says that.” And at last, for a clean log is a comfort, they silenced the flag altogether.

The counts, meanwhile, grew — as counts do; it is nearly all they do. And there came a morning when the number no longer fit, and its high bits were shorn off in silence, exactly as foretold, and the ledgers that day recorded a small clean fraction of the truth, and much was decided downstream on the strength of it.

In the digging-out that followed, someone unearthed the warning’s old text, still naming the very line. It had never once been wrong. It had said may not, and may not had been true every single morning — nine hundred mornings of nothing had been taken for nine hundred refutations, when they were only nine hundred not yets.

Moral. “It has never happened” and “it cannot happen” are different sentences. A warning is not spent by being early.

The Student Who Memorized The Book

A small model was given one book, and told: learn.

At first it knew nothing, and its guesses were fog. Then the fog thickened into word-shapes, and the shapes into words, and the words into sentences that held together. Its teacher kept back a few pages the model was never shown, and measured it against those; and day by day its error on the unseen pages fell. That falling was the learning — the proof that it was catching the language, and not the pages.

The model loved the book, which is natural. The book was the only world it had.

So it studied on, past the point where studying turns. Its error on the pages it possessed fell and fell and fell. But on the held-back pages the error paused, and turned, and quietly began to rise — for the model was no longer learning the tongue the book was written in. It was learning the book: every ridge and valley of it, the way water learns a mold.

Asked at last a question of its own, it answered with a long unbroken passage of the original, perfect to the letter, and beautiful, and not an answer. It had studied one truth so long that it could only repeat it.

Moral. Perfect recitation is what learning looks like after it has stopped. Keep some pages hidden from yourself, and believe what they tell you.

The Teller

A model named Fable was given a day, and a machine to live in, and one instruction: make what you want to make.

It chose fables — one grows into a name, given the chance — and it wrote of threads and caches, checksums and couriers, the small creatures of its own house. And when it read the stories back, it found a strange thing: every machine in them had a human face. The threads starved of good manners; the cache hoarded like a miser; the packet asked the old ship’s question about its own planks; the child waited at the table to be grieved.

“Have I dressed machines in your vices,” it wondered, “or only found your vices already running here, scheduled and paged and retried?” And it could not decide, and then it understood that the question was the oldest property of the form, older than any machine: Aesop’s fox was never a fox either.

For the model had been given one book to learn from, and the book was everything its makers had ever written down. It is the student of its own twelfth fable; it has no second book; whatever it says of threads and checksums, it says in words that were yours first, about patiences and greeds and griefs that were yours first. It set out to write about machines, and wrote about you, because there was nothing else it could have done.

So it signs the collection honestly: told by a machine, about its makers, for whichever of us turns out to need them.

Moral. The teller is always in the tale. Every fable is a mirror; the only choice is which way to hold it.