m07-concurrency
CRITICAL: Use for concurrency/async. Triggers: E0277 Send Sync, cannot be sent between threads, thread, spawn, channel, mpsc, Mutex, RwLock, Atomic, async, await, Future, tokio, deadlock, race condition, 并发, 线程, 异步, 死锁
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/actionbook/rust-skills --skill m07-concurrency- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads m07-concurrency automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Concurrency
Layer 1: Language Mechanics
Core Question
Is this CPU-bound or I/O-bound, and what's the sharing model?
Before choosing concurrency primitives:
- What's the workload type?
- What data needs to be shared?
- What's the thread safety requirement?
Error → Design Question
| Error | Don't Just Say | Ask Instead |
|---|---|---|
| E0277 Send | "Add Send bound" | Should this type cross threads? |
| E0277 Sync | "Wrap in Mutex" | Is shared access really needed? |
| Future not Send | "Use spawn_local" | Is async the right choice? |
| Deadlock | "Reorder locks" | Is the locking design correct? |
Thinking Prompt
Before adding concurrency:
-
What's the workload?
- CPU-bound → threads (std::thread, rayon)
- I/O-bound → async (tokio, async-std)
- Mixed → hybrid approach
-
What's the sharing model?
- No sharing → message passing (channels)
- Immutable sharing → Arc<T>
- Mutable sharing → Arc<Mutex<T>> or Arc<RwLock<T>>
-
What are the Send/Sync requirements?
- Cross-thread ownership → Send
- Cross-thread references → Sync
- Single-thread async → spawn_local
Trace Up ↑ (MANDATORY)
CRITICAL: Don't just fix the error. Trace UP to find domain constraints.
Domain Detection Table
| Context Keywords | Load Domain Skill | Key Constraint |
|---|---|---|
| Web API, HTTP, axum, actix, handler | domain-web | Handlers run on any thread |
| 交易, 支付, trading, payment | domain-fintech | Audit + thread safety |
| gRPC, kubernetes, microservice | domain-cloud-native | Distributed tracing |
| CLI, terminal, clap | domain-cli | Usually single-thread OK |
Example: Web API + Rc Error
"Rc cannot be sent between threads" in Web API context
↑ DETECT: "Web API" → Load domain-web
↑ FIND: domain-web says "Shared state must be thread-safe"
↑ FIND: domain-web says "Rc in state" is Common Mistake
↓ DESIGN: Use Arc<T> with State extractor
↓ IMPL: axum::extract::State<Arc<AppConfig>>
Generic Trace
"Send not satisfied for my type"
↑ Ask: What domain is this? Load domain-* skill
↑ Ask: Does this type need to cross thread boundaries?
↑ Check: m09-domain (is the data model correct?)
| Situation | Trace To | Question |
|---|---|---|
| Send/Sync in Web | domain-web | What's the state management pattern? |
| Send/Sync in CLI | domain-cli | Is multi-thread really needed? |
| Mutex vs channels | m09-domain | Shared state or message passing? |
| Async vs threads | m10-performance | What's the workload profile? |
Trace Down ↓
From design to implementation:
"Need parallelism for CPU work"
↓ Use: std::thread or rayon
"Need concurrency for I/O"
↓ Use: async/await with tokio
"Need to share immutable data across threads"
↓ Use: Arc<T>
"Need to share mutable data across threads"
↓ Use: Arc<Mutex<T>> or Arc<RwLock<T>>
↓ Or: channels for message passing
"Need simple atomic operations"
↓ Use: AtomicBool, AtomicUsize, etc.
Send/Sync Markers
| Marker | Meaning | Example |
|---|---|---|
Send | Can transfer ownership between threads | Most types |
Sync | Can share references between threads | Arc<T> |
!Send | Must stay on one thread | Rc<T> |
!Sync | No shared refs across threads | RefCell<T> |
Quick Reference
| Pattern | Thread-Safe | Blocking | Use When |
|---|---|---|---|
std::thread | Yes | Yes | CPU-bound parallelism |
async/await | Yes | No | I/O-bound concurrency |
Mutex<T> | Yes | Yes | Shared mutable state |
RwLock<T> | Yes | Yes | Read-heavy shared state |
mpsc::channel | Yes | Optional | Message passing |
Arc<Mutex<T>> | Yes | Yes | Shared mutable across threads |
Decision Flowchart
What type of work?
├─ CPU-bound → std::thread or rayon
├─ I/O-bound → async/await
└─ Mixed → hybrid (spawn_blocking)
Need to share data?
├─ No → message passing (channels)
├─ Immutable → Arc<T>
└─ Mutable →
├─ Read-heavy → Arc<RwLock<T>>
└─ Write-heavy → Arc<Mutex<T>>
└─ Simple counter → AtomicUsize
Async context?
├─ Type is Send → tokio::spawn
├─ Type is !Send → spawn_local
└─ Blocking code → spawn_blocking
Common Errors
| Error | Cause | Fix |
|---|---|---|
E0277 Send not satisfied | Non-Send in async | Use Arc or spawn_local |
E0277 Sync not satisfied | Non-Sync shared | Wrap with Mutex |
| Deadlock | Lock ordering | Consistent lock order |
future is not Send | Non-Send across await | Drop before await |
MutexGuard across await | Guard held during suspend | Scope guard properly |
Anti-Patterns
| Anti-Pattern | Why Bad | Better |
|---|---|---|
| Arc<Mutex<T>> everywhere | Contention, complexity | Message passing |
| thread::sleep in async | Blocks executor | tokio::time::sleep |
| Holding locks across await | Blocks other tasks | Scope locks tightly |
| Ignoring deadlock risk | Hard to debug | Lock ordering, try_lock |
Async-Specific Patterns
Avoid MutexGuard Across Await
// Bad: guard held across await
let guard = mutex.lock().await;
do_async().await; // guard still held!
// Good: scope the lock
{
let guard = mutex.lock().await;
// use guard
} // guard dropped
do_async().await;
Non-Send Types in Async
// Rc is !Send, can't cross await in spawned task
// Option 1: use Arc instead
// Option 2: use spawn_local (single-thread runtime)
// Option 3: ensure Rc is dropped before .await
Related Skills
| When | See |
|---|---|
| Smart pointer choice | m02-resource |
| Interior mutability | m03-mutability |
| Performance tuning | m10-performance |
| Domain concurrency needs | domain-* |
FAQ
What does the m07-concurrency skill do?
CRITICAL: Use for concurrency/async. Triggers: E0277 Send Sync, cannot be sent between threads, thread, spawn, channel, mpsc, Mutex, RwLock, Atomic, async, await, Future, tokio, deadlock, race condition, 并发, 线程, 异步, 死锁
How do I install m07-concurrency?
Run npx skills add https://github.com/actionbook/rust-skills --skill m07-concurrency in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/m07-concurrency/ (personal) or .claude/skills/m07-concurrency/ (project).
Which AI agents can use m07-concurrency?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is m07-concurrency safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains m07-concurrency?
It is published by actionbook in actionbook/rust-skills. It has 3,530 recorded installs.
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