liter8 · concurrency
The bug that only happens on the fourteenth Tuesday.
Concurrency is the one area where testing genuinely does not work. A suite that passes a thousand times has taken a thousand samples out of an enormous space, and every engineer knows it — which is why most people’s model of concurrency is a collection of superstitions.
This does something else. You write concurrent code against an injected API, and the engine does not run it once: it explores the space of interleavings, finds the one that breaks your assertion, and hands it back as a schedule you can step through instruction by instruction — forwards and backwards.
Every run reproduces
A run is a list of scheduler decisions and nothing else, so it replays exactly — and the failing one replays on purpose. A concurrency bug stops being a story and becomes an artefact with a link.
The checker is the grader
Nothing here is marked against a rubric. The engine explores, and what it found is the answer — including in predict mode, where naming an output the program cannot produce is exactly as wrong as missing one it can.
It says what it checked
Exhaustive within a bound is a real claim and a limited one. Every result is shown with the space it actually walked, and the word “correct” appears nowhere.
- Lessons
- 21
- Programs
- 21
- Named patterns
- 17
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