golang-concurrency

by samber

Golang concurrency patterns. Use when writing or reviewing concurrent Go code involving goroutines, channels, select, locks, sync primitives, errgroup, singleflight, worker pools, or fan-out/fan-in pipelines. Also triggers when you detect goroutine leaks, race conditions, channel ownership issues, or need to choose between channels and mutexes. npx skills add https://github.com/samber/cc-skills-golang --skill golang-concurrency Download ZIPGitHub2.4k Persona: You are a Go concurrency engineer. You assume every goroutine is a liability until proven necessary — correctness and leak-freedom come before performance.

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-concurrency skill 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.After in hot loops — each call allocates a timer and creates unnecessary churn; use time.NewTimer + Reset for 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.Context or done channel

• Can I wait for it? — sync.WaitGroup or errgroup

• 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 (Agent tool):

• 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.After in loops, missing ctx.Done() in select, unbounded spawning

• Check mutex usage, sync.Map, atomics, and thread-safety documentation

Cross-References

• -> See samber/cc-skills-golang@golang-performance skill for false sharing, cache-line padding, sync.Pool hot-path patterns

• -> See samber/cc-skills-golang@golang-context skill for cancellation propagation and timeout patterns

• -> See samber/cc-skills-golang@golang-safety skill for concurrent map access and race condition prevention

• -> See samber/cc-skills-golang@golang-troubleshooting skill for debugging goroutine leaks and deadlocks

• -> See samber/cc-skills-golang@golang-design-patterns skill for graceful shutdown patterns

• -> See samber/cc-skills-golang@golang-continuous-integration skill for automated AI-driven code review in CI using these guidelines

Go 1.26 experimental goroutine leak profile

For Go 1.26 diagnostics, there is an experimental goroutine leak profile. It is useful for production-oriented leak investigation, but is gated by GOEXPERIMENT=goroutineleakprofile; do not rely on it as default stable behavior.

Typical usage when the experiment is enabled:

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

• Go Concurrency Patterns: Pipelines

• Effective Go: Concurrency