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AsyncQueuer: concurrency > 1 not honoured for items added while another is executing (regression in 0.22.0)

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#269 0 comentarios 0 reacciones 0 asignados Ver en GitHub

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@KevinVandy ya está trabajando en esto.

Desde el 30/9/2026.

  • #271 de @KevinVandy — abierto

Evaluación

Dificultad
3/5
Tiempo estimado
1-2 días
Aptitud para principiantes
66/100
Tipo de issue
Error
Claridad
Bastante claro
Estado de actividad
Activo
Stack tecnológico
node.js, typescript
Área
backend

Línea de trabajo

Start with the AsyncQueuer addItem path and its private #tick logic, especially the pendingTick guard described in the issue. Run the linked gist with @tanstack/pacer 0.22.0 and 0.21.1 to compare behavior. Done means adding items while an execution is pending fills every available concurrency slot without bypassing wait behavior.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

TanStack Pacer version

@tanstack/pacer v0.22.0 (via @tanstack/react-pacer v0.23.0). Last working version: @tanstack/pacer v0.21.1 (@tanstack/react-pacer v0.22.1).

Framework/Library version

Reproduced with the core package on Node.js v25.9.0 (no framework). Originally seen through useAsyncQueuer with React v19.3.0.

Describe the bug and the steps to reproduce it

Since @tanstack/pacer 0.22.0, an AsyncQueuer with concurrency: 2 runs items one at a time when they are added one after another, for example one addItem() per user click. The second item waits for the first to finish even though a concurrency slot is free. On 0.21.1 both start immediately.

Steps:

  1. Create an AsyncQueuer with { concurrency: 2, wait: 0 } and a task that stays pending (a long download, say).
  2. Call addItem("a"), then addItem("b").
  3. Check how many tasks have started.

Expected: 2 started, 2 active, 0 pending (what 0.21.1 does).
Actual on 0.22.0: 1 started, 1 active, 1 pending.

import { AsyncQueuer } from "@tanstack/pacer";

let started = 0;
const queuer = new AsyncQueuer(
  async () => {
    started++;
    await new Promise(() => {}); // a long-running task
  },
  { concurrency: 2, wait: 0 },
);

queuer.addItem("a");
queuer.addItem("b");

await new Promise((r) => setTimeout(r, 50));
const { activeItems, items } = queuer.store.state;
console.log({ started, active: activeItems.length, pending: items.length });
@tanstack/pacer output
0.21.1 started=2 active=2 pending=0
0.22.0 started=1 active=1 pending=1

Likely cause: #246 (the fix for #188) keeps pendingTick: true while executions are in flight (#tick: "pendingTick must stay true while executions or wait timers are pending"), and addItem only calls #tick() when !pendingTick. So an item added during an execution isn't picked up until that execution settles and re-ticks, even though a slot is free. main still has the same guard. The #188 intent (don't bypass wait) seems to need the guard only while a wait timer is armed, not while an execution runs with free slots.

(Investigated with AI assistance. The repro and the version comparison above were run and checked by hand.)

Your Minimal, Reproducible Example - (Sandbox Highly Recommended)

https://gist.github.com/ilyaauditoo/710aab918995470c11960aa9e33ff0f0 — npm install && npm start (pins @tanstack/[email protected]; change it to 0.21.1 to see the expected behaviour).

Screenshots or Videos (Optional)

No response

Do you intend to try to help solve this bug with your own PR?

Yes, I think I know how to fix it and will discuss it in the comments of this issue

Terms & Code of Conduct
  • I agree to follow this project's Code of Conduct
  • I understand that if my bug cannot be reliable reproduced in a debuggable environment, it will probably not be fixed and this issue may even be closed.
Lenguaje dominante
TypeScript
Estrellas
776
Forks
67
Merge medio
1 d 15 h
PR fusionados (30 d)
11

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Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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