# csharp-concurrency-patterns

Guides AI agents in selecting the right .NET concurrency abstractions, from async/await to Channels and Akka.NET. Useful when refactoring work queues and eliminating thread locks.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1600 installs · ★ 1238
- Author: Aaronontheweb
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/Aaronontheweb/dotnet-skills/tree/HEAD/skills/csharp-concurrency-patterns/SKILL.md
- Updated: 2026-10-11
- HTML: https://affpapa.org/en/nevibecode/skills/csharp-concurrency-patterns

## What it does

The skill provides the agent with a structured decision tree for .NET concurrency. It establishes `async/await` as the standard baseline for I/O waits and non-blocking tasks. When operations are CPU-bound, it steers the design toward `Parallel.ForEachAsync` with explicit concurrency limits.

For producer-consumer workflows, it defaults to bounded `System.Threading.Channels`. Higher-level requirements involving backpressure, server-side batching, or independent entity states escalate to Akka.NET Streams and actors.

Manual synchronization via `lock` or semaphores is treated as a last resort. If an agent tries to guard domain state with locks, the skill guides it toward immutability or serialized channel messaging.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill csharp-concurrency-patterns -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/csharp-concurrency-patterns/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/csharp-concurrency-patterns/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill csharp-concurrency-patterns -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/csharp-concurrency-patterns/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill csharp-concurrency-patterns -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/csharp-concurrency-patterns/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install Aaronontheweb/dotnet-skills csharp-concurrency-patterns
```

2. **Manually: put the files in place**
- File: `.github/skills/csharp-concurrency-patterns/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill csharp-concurrency-patterns -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/Aaronontheweb/dotnet-skills --path skills/csharp-concurrency-patterns
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/csharp-concurrency-patterns/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add Aaronontheweb/dotnet-skills --skill csharp-concurrency-patterns -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/Aaronontheweb/dotnet-skills/tree/HEAD/skills/csharp-concurrency-patterns/SKILL.md

## When to use it
- choose the correct concurrency abstraction for .NET workloads
- replace manual lock primitives with bounded Channels
- process collections in parallel using Parallel.ForEachAsync
- manage state across independent entities via Akka.NET actors

## Example prompts
- Design an in-memory order queue using System.Threading.Channels with backpressure.
- Refactor this locked dictionary cache to avoid shared mutable state.
- Process a list of image records with Parallel.ForEachAsync and a CancellationToken.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 8f709d8528465112.

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````text
---
name: csharp-concurrency-patterns
description: Choosing the right concurrency abstraction in .NET - from async/await for I/O to Channels for producer/consumer to Akka.NET for stateful entity management. Avoid locks and manual synchronization unless absolutely necessary.
user-invocable: false
---

# .NET Concurrency: Choosing the Right Tool

## When to Use This Skill

Use this skill when:
- Deciding how to handle concurrent operations in .NET
- Evaluating whether to use async/await, Channels, Akka.NET, or other abstractions
- Tempted to use locks, semaphores, or other synchronization primitives
- Need to process streams of data with backpressure, batching, or debouncing
- Managing state across multiple concurrent entities

## Reference Files

- [advanced-concurrency.md](advanced-concurrency.md): Akka.NET Streams, Reactive Extensions, Akka.NET Actors (entity-per-actor, state machines, cluster sharding), and async local function patterns

## The Philosophy

**Start simple, escalate only when needed.**

Most concurrency problems can be solved with `async/await`. Only reach for more sophisticated tools when you have a specific need that async/await can't address cleanly.

**Try to avoid shared mutable state.** The best way to handle concurrency is to design it away. Immutable data, message passing, and isolated state (like actors) eliminate entire categories of bugs.

**Locks should be the exception, not the rule.** When you can't avoid shared mutable state:
1. **First choice:** Redesign to avoid it (immutability, message passing, actor isolation)
2. **Second choice:** Use `System.Collections.Concurrent` (ConcurrentDictionary, etc.)
3. **Third choice:** Use `Channel<T>` to serialize access through message passing
4. **Last resort:** Use `lock` for simple, short-lived critical sections

---

## Decision Tree

```
What are you trying to do?
│
├─► Wait for I/O (HTTP, database, file)?
│   └─► Use async/await
│
├─► Process a collection in parallel (CPU-bound)?
│   └─► Use Parallel.ForEachAsync
│
├─► Producer/consumer pattern (work queue)?
│   └─► Use System.Threading.Channels
│
├─► UI event handling (debounce, throttle, combine)?
│   └─► Use Reactive Extensions (Rx)
│
├─► Server-side stream processing (backpressure, batching)?
│   └─► Use Akka.NET Streams
│
├─► State machines with complex transitions?
│   └─► Use Akka.NET Actors (Become pattern)
│
├─► Manage state for many independent entities?
│   └─► Use Akka.NET Actors (entity-per-actor)
│
├─► Coordinate multiple async operations?
│   └─► Use Task.WhenAll / Task.WhenAny
│
````
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