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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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@KevinVandy 已经在做这个了。

开始于 2026年9月30日。

  • #271 来自 @KevinVandy —— 未关闭

评估

难度
3/5
预计耗时
1-2 天
新手友好度
66/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
活跃
技术栈
node.js, typescript
领域
backend

调研方向

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.

由索引模型根据 Issue 内容生成。

描述

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.
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环境准备

从这里开始

  1. 先读完整个 Issue，再读项目的贡献指南。
  2. 在 Issue 下留言说明你要接手 —— 这能避免两个人做同样的事。
  3. Fork 仓库，在一个分支上完成修改。
  4. 提交 Pull Request，并在描述里引用这个 Issue 编号。

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