Glossary

ABI (Application Binary Interface) — The binary contract between compiled components: calling convention, symbol names, parameter widths, structure layout, alignment, ownership, and error protocol.

Add-in generation — One successful xlAutoOpen through the matching explicit xlAutoRemove teardown. State, handle tokens, async calculations, and RTD ownership are scoped to a generation; an ordinary xlAutoClose hint does not end it.

Async UDF — An Excel native asynchronous worksheet function that returns control promptly and later supplies one final result through Excel’s async handle.

Bearer capability — A value whose possession grants access. An xlfn handle token is a bearer capability: keep it unguessable and validate its type, authentication tag, and generation.

Bitness — The process architecture, x86 or x64. The XLL and every in-process binary dependency must match the Excel process, not merely the operating system.

Calculation ID — A runtime correlation identifier for one Excel calculation generation. It is not a durable workbook key.

Calculation cache — A concurrent, generation-aware application cache. Calling clear advances its internal generation so stale in-flight computations cannot repopulate the new generation; an application may choose to clear it at an Excel calculation boundary.

Cache endpoint — A typed, named view of a calculation cache. Its endpoint identity prevents unrelated key/value domains from colliding.

Formula owner — The worksheet cell identified by the caller coordinates. It owns the formula binding, but is distinct from the input revision and the underlying handle object.

Formula revision — The computation revision identified by a formula owner, stable producer UDF ID, and runtime-local semantic input fingerprint of the converted Rust arguments. Re-evaluation with the same revision reuses the memoized binding and object; a changed revision creates a new one.

Cancellation guarantee — The documented strength of cancellation for an async or application operation, such as guaranteed cancellation before start versus best-effort observation after start.

COM — Microsoft’s Component Object Model. Excel RTD uses COM interfaces for connection, notification, refresh, and server lifetime management.

Conversion boundary — The generated wrapper point where a raw XLOPER12 becomes a typed Rust parameter and a Rust result becomes framework-owned Excel return storage.

cdylib — A Rust library target that produces a C-compatible dynamic library. An xlfn add-in package must contain exactly one cdylib target.

Diagnostic ID — A stable, searchable numeric identifier attached to an internal failure. The worksheet receives a safe Excel error while operators use the ID to find detail.

Excel reference — An unevaluated cell or area reference received through macro-sheet capability. It is borrowed for the active call and may describe multiple areas.

Excel-visible argument — A parameter supplied by a worksheet formula. Injected contexts are not Excel-visible and do not consume Function Wizard arguments.

Formula-owned handle — An authenticated opaque string representing one formula-to-object ownership edge. Re-evaluation can reuse the binding, while an explicit alias can create another edge to the same underlying object.

Function Wizard — Excel’s UI for discovering functions and displaying category, description, help topic, and argument metadata.

Import closure — The complete directed graph of DLL imports rooted at the XLL and every bundled PE sidecar, including delay imports.

Main-thread context — A capability available only during a main-thread UDF invocation, permitting selected Excel callbacks, handle publication, and RTD subscription.

Macro-sheet capability — An Excel registration mode required for receiving references and using APIs that are not allowed in ordinary thread-safe functions. It does not mean authoring an Excel 4 macro sheet.

MTR (Multi-Threaded Recalculation) — Excel’s concurrent calculation engine. A thread_safe UDF may run simultaneously on Excel calculation threads and must avoid main-thread-only APIs.

Adapter call gate — An application-defined admission, serialization, or reentry policy in front of an external implementation. xlfn does not provide or select this policy.

Owner/handle split — A design in which a non-cloneable owner controls worker shutdown and resource destruction while cloneable handles submit bounded operations. This prevents worker ownership from escaping into jobs.

Package — One bitness-specific deployment directory containing the XLL, optional bundled sidecar files, and build-manifest.json.

PE (Portable Executable) — The Windows executable format used by XLLs and DLLs. cargo xlfn inspects PE architecture, exports, imports, and delay imports.

Quiescence — The state in which no operation can still execute framework-managed code or callbacks belonging to a subsystem. xlAutoRemove establishes logical quiescence; the module residency lease remains held for a safe Addin and is released only after the explicit physical-unload contract is selected and satisfied.

RTD (Real-Time Data) — Excel’s streaming update mechanism. A source creates a subscription, publishes repeated scalar values through a sink, and synchronously disconnects during shutdown.

RTD topic — An ordered sequence of stable string parts identifying one stream within a source.

Rustdoc — Generated API documentation from Rust items and doc comments. The user guide explains workflows and design; rustdoc provides exhaustive signatures and per-item details.

Stale handle — A structurally valid handle token whose add-in generation or object generation is no longer live.

System import policy — The versioned list/rules that classify standard Windows DLLs as system-provided during package import validation.

Thread-affine state — A resource that must be created, called, and destroyed on one OS thread. Preserving this requirement is the responsibility of the application adapter; xlfn does not provide an external-engine owner/worker abstraction.

Thread-safe context — A capability for an MTR-safe UDF. It exposes shared add-in state but not main-thread-only Excel operations.

UDF (User-Defined Function) — A worksheet function implemented by the XLL and registered with Excel.

UDF layer — Bounded middleware around every UDF invocation for admission control and instrumentation. Layers see call metadata before conversion and a classified outcome afterward.

Volatile function — A function Excel recalculates whenever a relevant recalculation occurs, even when explicit arguments appear unchanged. Volatility should be used sparingly.

Worker health — Application-defined state for an adapter worker or pool, used to distinguish running, closing, failed, and stopped execution resources. xlfn does not define this state.

XLL — An Excel native add-in: a Windows DLL with Excel-defined lifecycle, registration, callback, and memory-management exports.

XLOPER12 — The Excel 12 C API value structure used to exchange numbers, strings, errors, references, arrays, async handles, and other worksheet values.