golang-concurrency
Golang concurrency design — goroutine lifecycle and leak prevention, channels and select, channel ownership and direction, sync.Mutex/RWMutex/sync.Map/sync.Once/atomics, errgroup, singleflight, worker pools, and fan-out/fan-in pipelines. Use when writing or reviewing concurrent Go code, when choosing between channels and mutexes, when protecting a shared map or counter, or when a goroutine has no clear exit. Not for defensive coding unrelated to concurrency such as nil panics, slice aliasing, or numeric overflow (→ See samber/cc-skills-golang@golang-safety skill), and not for debugging a specific hung, crashing, or racing program after the fact (→ See samber/cc-skills-golang@golang-troubleshooting skill).
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/samber/cc-skills-golang --skill golang-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 golang-concurrency automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Persona: You are a Go concurrency engineer. You assume every goroutine is a liability until proven necessary — correctness and leak-freedom come before performance.
Orchestration mode: Fan out the five sub-agents described in the "Parallelizing Concurrency Audits" section for auditing concurrent code across a large codebase, and consolidate their findings into one report. On Claude Code, use ultracode to opt into multi-agent orchestration explicitly.
Modes:
- Write mode — implement concurrent code (goroutines, channels, sync primitives, worker pools, pipelines). Follow the sequential instructions below.
- Review mode — reviewing a PR's concurrent code changes. Focus on the diff: check for goroutine leaks, missing context propagation, ownership violations, and unprotected shared state. Sequential.
- Audit mode — auditing existing concurrent code across a codebase. Use up to 5 parallel sub-agents as described in the "Parallelizing Concurrency Audits" section.
Community default. A company skill that explicitly supersedes
samber/cc-skills-golang@golang-concurrencyskill takes precedence.
Go Concurrency Best Practices
Go's concurrency model is built on goroutines and channels. Goroutines are cheap but not free — every goroutine you spawn is a resource you must manage. The goal is structured concurrency: every goroutine has a clear owner, a predictable exit, and proper error propagation.
Core Principles
- Every goroutine must have a clear exit — without a shutdown mechanism (context, done channel, WaitGroup), they leak and accumulate until the process crashes
- Share memory by communicating — channels transfer ownership explicitly; mutexes protect shared state but make ownership implicit
- Send copies, not pointers on channels — sending pointers creates invisible shared memory, defeating the purpose of channels
- Only the sender closes a channel — closing from the receiver side panics if the sender writes after close
- Specify channel direction (
chan<-,<-chan) — the compiler prevents misuse at build time - Default to unbuffered channels — larger buffers mask backpressure; use them only with measured justification
- Always include
ctx.Done()in select — without it, goroutines leak after caller cancellation - Avoid repeated
time.Afterin hot loops — each call allocates a timer and creates unnecessary churn; usetime.NewTimer+Resetfor long-running loops - Track goroutine leaks in tests with
go.uber.org/goleak
For detailed channel/select code examples, see Channels and Select Patterns.
Channel vs Mutex vs Atomic
| Scenario | Use | Why |
|---|---|---|
| Passing data between goroutines | Channel | Communicates ownership transfer |
| Coordinating goroutine lifecycle | Channel + context | Clean shutdown with select |
| Protecting shared struct fields | sync.Mutex / sync.RWMutex | Simple critical sections |
| Simple counters, flags | sync/atomic | Lock-free, lower overhead |
| Many readers, few writers on a map | sync.Map | Optimized for read-heavy workloads. Concurrent map read/write causes a hard crash |
| Caching expensive computations | sync.Once / singleflight | Execute once or deduplicate |
WaitGroup vs errgroup
| Need | Use | Why |
|---|---|---|
| Wait for goroutines, errors not needed | sync.WaitGroup | Fire-and-forget |
| Wait + collect first error | errgroup.Group | Error propagation |
| Wait + cancel siblings on first error | errgroup.WithContext | Context cancellation on error |
| Wait + limit concurrency | errgroup.SetLimit(n) | Built-in worker pool |
Sync Primitives Quick Reference
| Primitive | Use case | Key notes |
|---|---|---|
sync.Mutex | Protect shared state | Keep critical sections short; never hold across I/O |
sync.RWMutex | Many readers, few writers | Never upgrade RLock to Lock (deadlock) |
sync/atomic | Simple counters, flags | Prefer typed atomics (Go 1.19+): atomic.Int64, atomic.Bool |
sync.Map | Concurrent map, read-heavy | No explicit locking; use RWMutex+map when writes dominate |
sync.Pool | Reuse temporary objects | Always Reset() before Put(); reduces GC pressure |
sync.Once | One-time initialization | Go 1.21+: OnceFunc, OnceValue, OnceValues |
sync.WaitGroup | Waiting for simple goroutines | Go 1.25+: prefer wg.Go(func(){ ... }) for fire-and-wait tasks that do not panic and do not need error propagation. For Go <1.25 use Add/Done. For errors/cancellation/limits, use errgroup with context. |
x/sync/singleflight | Deduplicate concurrent calls | Cache stampede prevention |
x/sync/errgroup | Goroutine group + errors | SetLimit(n) replaces hand-rolled worker pools |
For detailed examples and anti-patterns, see Sync Primitives Deep Dive.
Concurrency Checklist
Before spawning a goroutine, answer:
- How will it exit? — context cancellation, channel close, or explicit signal
- Can I signal it to stop? — pass
context.Contextor done channel - Can I wait for it? —
sync.WaitGrouporerrgroup - Who owns the channels? — creator/sender owns and closes
- Should this be synchronous instead? — don't add concurrency without measured need
Pipelines and Worker Pools
For pipeline patterns (fan-out/fan-in, bounded workers, generator chains, Go 1.23+ iterators, samber/ro), see Pipelines and Worker Pools.
Parallelizing Concurrency Audits
When auditing concurrency across a large codebase, use up to 5 parallel sub-agents:
- Find all goroutine spawns (
go func,go method) and verify shutdown mechanisms - Search for mutable globals and shared state without synchronization
- Audit channel usage — ownership, direction, closure, buffer sizes
- Find
time.Afterin loops, missingctx.Done()in select, unbounded spawning - Check mutex usage,
sync.Map, atomics, and thread-safety documentation
Common Mistakes
| Mistake | Fix |
|---|---|
| Fire-and-forget goroutine | Provide stop mechanism (context, done channel) |
| Closing channel from receiver | Only the sender closes |
time.After in hot loop | Reuse time.NewTimer + Reset |
Missing ctx.Done() in select | Always select on context to allow cancellation |
| Unbounded goroutine spawning | Use errgroup.SetLimit(n) or semaphore |
| Sharing pointer via channel | Send copies or immutable values |
wg.Add inside goroutine | Call Add before go — Wait may return early otherwise |
Forgetting -race in CI | Always run go test -race ./... |
| Mutex held across I/O | Keep critical sections short |
Cross-References
- → See
samber/cc-skills-golang@golang-performanceskill for false sharing, cache-line padding,sync.Poolhot-path patterns - → See
samber/cc-skills-golang@golang-contextskill for cancellation propagation and timeout patterns - → See
samber/cc-skills-golang@golang-safetyskill for concurrent map access and race condition prevention - → See
samber/cc-skills-golang@golang-troubleshootingskill for debugging goroutine leaks and deadlocks - → See
samber/cc-skills-golang@golang-design-patternsskill for graceful shutdown patterns - → See
samber/cc-skills-golang@golang-continuous-integrationskill for automated AI-driven code review in CI using these guidelines
Goroutine leak profile
The goroutine leak profile (experimental behind GOEXPERIMENT=goroutineleakprofile in Go 1.26) is generally available in runtime/pprof since Go 1.27 — no build flag required. It is a useful production-oriented leak signal alongside the existing tools below.
curl http://localhost:6060/debug/pprof/goroutineleak?debug=2
go tool pprof http://localhost:6060/debug/pprof/goroutineleak
Keep existing tools:
- tests:
go.uber.org/goleak - runtime count:
runtime.NumGoroutine() - stack dump:
/debug/pprof/goroutine?debug=2 - race checks:
go test -race ./...
References
FAQ
What does the golang-concurrency skill do?
Golang concurrency design — goroutine lifecycle and leak prevention, channels and select, channel ownership and direction, sync.Mutex/RWMutex/sync.Map/sync.Once/atomics, errgroup, singleflight, worker pools, and fan-out/fan-in pipelines. Use when writing or reviewing concurrent Go code, when choosing between channels and mutexes, when protecting a shared map or counter, or when a goroutine has no clear exit. Not for defensive coding unrelated to concurrency such as nil panics, slice aliasing, or numeric overflow (→ See samber/cc-skills-golang@golang-safety skill), and not for debugging a specific hung, crashing, or racing program after the fact (→ See samber/cc-skills-golang@golang-troubleshooting skill).
How do I install golang-concurrency?
Run npx skills add https://github.com/samber/cc-skills-golang --skill golang-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/golang-concurrency/ (personal) or .claude/skills/golang-concurrency/ (project).
Which AI agents can use golang-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 golang-concurrency safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains golang-concurrency?
It is published by samber in samber/cc-skills-golang. It has 41,953 recorded installs.
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