Glossary

:=: Go’s short declaration. In a new block it declares every name on its left, even if a variable with that name exists outside the block.; The cancel function that stays nil
`%` in C: The remainder of an integer division. Its sign follows the left operand: -7 % 3 is -1, and -6 % 3 is 0.; A remainder of zero
`argv[2]`: The third word of the command. For MOVE key 5, it is the string "5".; A database called notanumber
`atoi`: A C function that turns the start of a string into an int. It stops at the first character that is not a digit, and returns 0 when there is no number at all. It never reports an error.; A database called notanumber
`Date.new(year, month, -1)`: In Ruby, day -1 means the last day of that month. .day then gives the number of days in the month.; The last Thursday of February
`drain`: Runs every queued job of one worker class until none is left. drain_all does it for all classes.; Sidekiq drain_all loops on a job outside its default queue
`IMPLEMENT_var_keylen_cipher`: Macro arguments, in order: algorithm, upper-case name, mode, upper-case mode, flags, key bits, block bits, IV bits, block or stream. The key bits set the default key length and appear in the table name, as in cast5128cbc_functions.; CAST5 CFB and OFB default to an 8-byte key
`selectDb`: Points the client at database id. It returns REDIS_ERR only when id is below 0 or not below the number of databases (16 by default).; A database called notanumber
`sigchain_push_common`: Pushes the same handler for SIGINT, SIGHUP, SIGTERM, SIGQUIT and SIGPIPE.; Two signal handlers, pushed in the wrong order
AbortSignal: An object you pass to fetch as signal. When it fires, the fetch stops and its promise rejects.; A fetch with no timeout
Alias: A name in the [alias] table of a Cargo config that expands to another command, here cargo foo to cargo a b.; A config parse error reported as an unknown command
asyncio.gather: Takes several tasks and returns one future that completes when all of them are done. Code waits for it with await.; A missing await on asyncio.gather
Atomic group `(?>...)`: Once the group has matched, the engine never goes back into it to try another way.; Regex backtracking on an email with too few words
Attribute breakout: A value placed inside attr="..." that contains a ". The quote ends the attribute early and the rest is read as new HTML.; A quote in a heading ID
Auto-commit: A connection mode where each statement is committed on its own. The incrementer turns it off to commit by hand.; A connection close skipped by a throw in finally
Background task: A task made with hass.async_create_background_task. Its docstring says it "Will be automatically cancelled on shutdown".; An OAuth task still waiting at shutdown
Backtracking: When part of a regex fails, the engine goes back and tries another way to match the earlier parts.; Regex backtracking on an email with too few words
Binding: bind:currentTime={x} keeps x and the playback position in sync, in both directions. set writes the position into x.; A timeupdate listener left on a removed audio element
BOM: Byte order mark: the character U+FEFF that some editors write at the very start of a UTF-8 file. It is invisible but counts as one character in a JavaScript string.; Offsets after stripping a BOM
BYDAY: The part of a repeat rule (RRULE) that names the weekday. BYDAY=4TH is the fourth Thursday, BYDAY=-1TH the last one.; The last Thursday of February
Cache key: The string a value is stored under. Two pieces of code that build the same key read and write the same value.; A rate limit key without the controller
CAST5: A block cipher with 64-bit blocks and keys of 5 to 16 bytes. Its normal key is 16 bytes (128 bits).; CAST5 CFB and OFB default to an 8-byte key
Cents: The smallest unit of the price. Stripe wants unit_amount as a whole number of cents: $19.99 is 1999.; Floating point error when converting dollars to cents
Closure: A function literal that uses variables from the code around it. It reads the variable itself, not a copy.; A loop variable captured by a goroutine
Column: A position inside one line. The HTML parser Vite uses counts columns from 1.; Off-by-one between a column and an offset
Connection pool: A set of open database connections that callers borrow and give back, so each query does not open a new one.; A connection counted but never pooled
Content script: Extension code that runs inside the inspected page and talks to the rest of the extension with chrome.runtime.sendMessage.; A fetch with no timeout
context.CancelFunc: The function returned by context.WithCancel. Calling it closes the context’s Done() channel and frees what waits on it.; The cancel function that stays nil
controller_path: The path name of a controller: "sessions" for SessionsController, "admin/users" for Admin::UsersController.; A rate limit key without the controller
Coroutine: A function defined with async def. Calling it does not run it to the end; something has to await it or schedule it.; A missing await on asyncio.gather
CRI: Container Runtime Interface: the gRPC API the kubelet uses to start, stop and remove containers in a runtime such as containerd.; An idempotent StopContainer in containerd
DataSource: The Java object that gives out database connections. It is often a pool that reuses a fixed number of them.; A connection close skipped by a throw in finally
Daylight saving time (DST): Clocks move one hour forward in spring and one hour back in autumn. The day they go back lasts 25 hours on the local clock.; Daylight saving time in monthly log rotation
defaults: A module-level dict in requests/defaults.py. It is created once, when the module is imported, and every session reads from it.; A headers dict shared by every session
Double-checked locking: Testing a field without the lock, then taking the lock and testing it again before building the value.; Double-checked locking: assign the field last
Drop: Rust runs a value’s destructor when the value goes away. Assigning a new value to a field drops the old one on that line.; A waker dropped while the JoinSet mutex is held
ECB, CBC, GCM: Three cipher modes: ECB uses no IV, CBC needs an IV of a fixed length, GCM accepts IVs of different lengths.; An empty IV that passed the length check
Embedded: An object whose data fits inside its own slot, so there is nothing else to free.; Hashes that were never freed
ERR_FAIL_NULL_MSG: A Godot macro that prints the message and returns from the function when the pointer is null.; The check one line too late
errdefs.IsNotFound: A containerd helper that tells whether an error means "this object does not exist".; An idempotent StopContainer in containerd
Exclusive end: An end offset that points just past the last character. slice(start, end) already stops before end.; One character past the template
Exit condition: The test a loop checks before each turn, here jobs.any?. The loop ends only when the body makes it false.; Sidekiq drain_all loops on a job outside its default queue
explicitTimeout: The duration prop as a number, or null when the component has no duration.; A duration of 0 that still animated
Facade: A Laravel class with static methods that forward each call to one object taken from the service container.; A locale that stays set
Fake mode: Sidekiq::Testing.fake!: pushed jobs go into in-memory arrays instead of Redis, so a test can inspect and run them.; Sidekiq drain_all loops on a job outside its default queue
Falsy: A value that if treats as false: 0, "", NaN, null, undefined and false.; A duration of 0 that still animated
finally: A Java block that runs after try and catch, whether they end normally or throw.; A connection close skipped by a throw in finally
Flag bit: A bit in the object header that records a fact about the object, tested with flags & SOME_FLAG.; Hashes that were never freed
Floating point: How JavaScript stores every number: in binary, with about 16 significant digits. Most decimal fractions, like 0.99, have no exact binary value.; Floating point error when converting dollars to cents
Future: An object for a result that will exist later. await future pauses the caller until the result is there.; A missing await on asyncio.gather
getTransitionInfo: Reads the CSS transition or animation of the element and returns its type and its total time.; A duration of 0 that still animated
GIL: The global interpreter lock in CPython. Only one thread runs Python bytecode at a time, but the interpreter can switch threads between two bytecode instructions.; Thread names from an unlocked counter
Goroutine: A function that Go runs at the same time as the code that started it, with go func() { ... }().; A loop variable captured by a goroutine
Idempotent: A call you can repeat: sending it twice leaves the same state and gives the same kind of answer as sending it once.; An idempotent StopContainer in containerd
Idle list: The open connections that no caller holds right now, kept in freeConn (at most 2 by default).; A connection counted but never pooled
if let Ok(x): Runs the block only when the value is Ok. On Err it skips the block, and the error is dropped.; A config parse error reported as an unknown command
int32: A signed 32-bit integer. Its largest value is 2,147,483,647, which is 2**31 minus 1.; Integer overflow in a NumPy element count
itertools.count: An iterator that yields 0, 1, 2 and so on. Its __next__ is written in C, so one call is a single step for Python code.; Thread names from an unlocked counter
IV: Initialization vector: extra bytes a cipher mixes into the first block. CBC mode needs one exactly as long as a block, 8 bytes for DES.; An empty IV that passed the length check
Lazy initialization: Building a value the first time someone asks for it, then reusing it.; Double-checked locking: assign the field last
Lazy quantifier `+?`: Matches as few characters as possible first, and takes one more each time the engine backtracks into it.; Regex backtracking on an email with too few words
Leader and follower: etcd members agree through Raft. One member is the leader (isPrimary() is true), the others are followers that apply the same log.; A lease heap that only the etcd leader empties
Lease: An etcd object with a time to live. When it expires or is revoked, the keys attached to it are deleted.; A lease heap that only the etcd leader empties
leaseExpiredNotifier: A heap of lease IDs ordered by expiry time, plus a map from ID to item. The leader polls it to find leases to revoke.; A lease heap that only the etcd leader empties
Log rotation: Renaming the current log file and starting a new one, here once per day, week or month.; Daylight saving time in monthly log rotation
Loop variable: The id, c of for id, c := range. Before Go 1.22 the loop declared them once and overwrote them on each turn.; A loop variable captured by a goroutine
max(): Python’s built-in that returns the largest item. On an empty sequence it raises ValueError, unless you pass default=.; A sitemap with nothing in it
multiply.reduce: NumPy’s product of all items. It first converts the input to an array, which stores Python ints as NumPy integers of a fixed width.; Integer overflow in a NumPy element count
Mutex: A lock that one thread holds at a time. This one cannot be taken twice by the same thread: the second lock() waits forever.; A waker dropped while the JoinSet mutex is held
Null dereference: Reading a field through a pointer that is null. In C++ this usually crashes the process.; The check one line too late
numOpen: The pool's count of open connections. With SetMaxOpenConns(n), callers wait once it reaches n.; A connection counted but never pooled
O(n²): Work that grows with the square of the input size: twice the entries, four times the work.; Copying a list from the head every time
OAuth: A login flow where the user signs in on another site, and that site then hands tokens back to the app.; An OAuth task still waiting at shutdown
Off-by-one: A count that is wrong by exactly one, often because one value starts at 0 and another at 1.; Off-by-one between a column and an offset
Offset: A position in the whole file, counted in characters from 0.; Off-by-one between a column and an offset
Offset: A position in the text, counted in characters from 0.; Offsets after stripping a BOM
Ordinal: The position of a weekday in its month: first, second, third, fourth, or last.; The last Thursday of February
os.path.abspath: Turns a path into an absolute one and resolves .. segments as text. It returns /tmp/x for /tmp/proj/../x.; A sibling folder with a longer name
Path traversal: A file name with .. segments, or an absolute path, that makes a write or a read leave the directory it was meant for.; A sibling folder with a longer name
Pending promise: A promise that is neither resolved nor rejected. Code chained on it with .then does not run.; A fetch with no timeout
Plane: One block of pixel data in a frame, for example the luma or one color channel. A row of it holds width values.; A remainder of zero
Precedence: The rules for how operators group when there are no parentheses. a && b && c must all be true; a parenthesis decides which part a condition belongs to.; An empty IV that passed the length check
Progress: A float that goes from 1 at the first frame of the transition to 0 at the last one.; A remainder of zero
Provider: In OpenSSL 3, the module that implements an algorithm. legacyprov.c maps names such as "CAST5-CFB" to these function tables.; CAST5 CFB and OFB default to an 8-byte key
Range formatting: Formatting only the code between rangeStart and rangeEnd, used by editors for "format selection".; Offsets after stripping a BOM
Rate limit: A cap on how many requests one client can make in a time window. Over the cap, the server answers 429.; A rate limit key without the controller
Read-modify-write: An update in three steps: read the value, compute the new one, store it. Another thread can run between the steps.; Thread names from an unlocked counter
RegExp.prototype.test: Returns true when the pattern matches. It converts a non-string argument to a string first.; An array that passes as a severity
Result: A Rust value that is either Ok(value) or Err(error). CargoResult<T> is Cargo’s name for a Result with its error type.; A config parse error reported as an unknown command
RID: A handle Godot uses to refer to an object owned by a server, here a texture. An empty RID points to nothing.; The check one line too late
Schematic: An Angular CLI script that edits the files of a project, here to migrate templates to the new control flow.; One character past the template
setdefault: d.setdefault(k, v) stores v under k if k is missing. It stores the object itself, not a copy of it.; A headers dict shared by every session
Setter: A set name(value) method. It runs when code assigns plan.amountDollars = ....; Floating point error when converting dollars to cents
Severity: How ESLint reports a rule: off, warning or error, written as 0, 1, 2 or as a string.; An array that passes as a severity
Shadowing: Declaring a variable in an inner block with the same name as one outside. Inside the block, the name means the new variable, and the outer one is not changed.; The cancel function that stays nil
Shallow copy: A copy of a container that holds the same inner objects as the original. Changing an inner dict through the copy changes it for both.; A headers dict shared by every session
sigchain: Git’s stack of signal handlers. sigchain_push puts a handler on top, sigchain_pop removes the top one. When a signal arrives, the handler on top runs.; Two signal handlers, pushed in the wrong order
SIGPIPE: The signal a process gets when it writes to a pipe that nobody reads any more. By default it kills the process.; Two signal handlers, pushed in the wrong order
Singleton: An object the container creates once and returns to every caller for the rest of the process.; A locale that stays set
Singly linked list: A chain of nodes where each one knows only the next. Finding the last node means walking from the first.; Copying a list from the head every time
Sitemap: A Django class that lists the URLs of a site section. items() returns the objects, and lastmod(item) returns when one object last changed.; A sitemap with nothing in it
Sitemap index: The top /sitemap.xml file. It links to each section and, since Django 4.1, gives each section a last modification date.; A sitemap with nothing in it
Source span: The start and end offsets of an element in the template text, as the Angular parser records them.; One character past the template
st_table: The hash table Ruby uses for bigger hashes. Its entries live in memory allocated with malloc, outside the object.; Hashes that were never freed
store.increment: Adds 1 to the counter saved under a key in the cache, creates it if missing, and returns the new value.; A rate limit key without the controller
SuspiciousOperation: The Django exception for input that looks like an attack. Here it stops the extraction.; A sibling folder with a longer name
Sweep: The phase of the garbage collector that walks dead objects and frees them.; Hashes that were never freed
Table of contents (ToC): The list of links to the headings of a page. Hugo builds its HTML in tocBuilder by writing strings to a buffer.; A quote in a heading ID
Tail pointer: A pointer kept to the last node, or to its next field, so an append does not have to walk the list.; Copying a list from the head every time
tap(): The Laravel helper tap($value, $callback) calls the callback with the value, then returns the value.; A locale that stays set
teardown: Svelte calls the function given to teardown when the effect is destroyed, here when the {#if} block removes the element.; A timeupdate listener left on a removed audio element
template.HTMLEscapeString: A Go function that replaces <, >, &, ' and " with HTML entities, so the browser reads them as text.; A quote in a heading ID
TextEncoder: The browser and Node API whose encode method turns a string into its UTF-8 bytes, as a Uint8Array.; Sizing a UTF-8 buffer with the string length
The ? operator: On Err, returns the error to the caller right away. On Ok, gives the value inside.; A config parse error reported as an unknown command
Time.mktime: Builds a Ruby Time from year, month, day (and more) in the local time zone.; Daylight saving time in monthly log rotation
timeupdate: An event a media element fires as its playback position changes.; A timeupdate listener left on a removed audio element
Tracked task: A task made with hass.async_create_task. Home Assistant keeps it in its _tasks set. If it is still running at the last shutdown stage, Home Assistant logs a warning and cancels it.; An OAuth task still waiting at shutdown
Type coercion: JavaScript converting a value to another type on its own, for example an array to a string.; An array that passes as a severity
Uint8Array view: new Uint8Array(buffer, offset, n) is a window of n bytes on existing memory. set copies into it and throws if the source is longer.; Sizing a UTF-8 buffer with the string length
UTF-16 code unit: What JavaScript strings are made of. str.length counts these units, not bytes.; Sizing a UTF-8 buffer with the string length
UTF-8: A text encoding where ASCII takes 1 byte and other characters take 2 to 4. 世 takes 3.; Sizing a UTF-8 buffer with the string length
volatile: A Java field modifier: a write to the field is seen right away by every thread that reads it.; Double-checked locking: assign the field last
Waker: A handle a future gives to whoever must wake it later. An executor can make its own waker type, with its own Drop code.; A waker dropped while the JoinSet mutex is held
Wraparound: When a fixed-width integer goes past its largest value, it continues from its smallest one instead of raising an error.; Integer overflow in a NumPy element count