---
title: <MergeQueue>
description: Queue tasks so at most maxConcurrency run; defaults to 1.
---

## Import

```tsx
import { MergeQueue } from "smithers-orchestrator";
```

## Props

| Prop | Type | Default | Description |
| --- | --- | --- | --- |
| `id` | `string` | auto-generated | Stable id for the queue group. |
| `maxConcurrency` | `number` | `1` | Max simultaneous child tasks. |
| `skipIf` | `boolean` | `false` | Skip the entire subtree. |
| `children` | `ReactNode` | -- | Child tasks/control-flow nodes. |

## Examples

### Single-lane (default)

```tsx
<MergeQueue>
  <Task id="lint" output={outputs.outputC}>{{ value: 1 }}</Task>
  <Task id="build" output={outputs.outputC}>{{ value: 2 }}</Task>
  <Task id="test" output={outputs.outputC}>{{ value: 3 }}</Task>
</MergeQueue>
```

### Custom concurrency

```tsx
<MergeQueue maxConcurrency={2}>
  {items.map((it, i) => (
    <Task key={i} id={`t${i}`} output={outputs.outputC}>{{ value: i }}</Task>
  ))}
</MergeQueue>
```

### Nesting with Parallel

```tsx
<Parallel maxConcurrency={3}>
  <MergeQueue>
    {items.map((it, i) => (
      <Task key={i} id={`q${i}`} output={outputs.outputC}>{{ value: i }}</Task>
    ))}
  </MergeQueue>
  <Task id="other" output={outputs.outputC}>{{ value: 99 }}</Task>
</Parallel>
```

The inner `<MergeQueue>` constrains its children to 1-at-a-time. The outer `<Parallel>` runs unrelated siblings concurrently up to its own limit.

## Internals

Renders as `<smithers:merge-queue>` (or `null` when skipped). Each child task receives `parallelGroupId` and `parallelMaxConcurrency` in its descriptor. The engine enforces the concurrency cap per group.

## Notes

- Defaults to single-lane (`maxConcurrency = 1`).
- Innermost group determines the effective cap for its descendants.
- Tasks outside the queue are unaffected by its limit.