Go Concurrency Safety Guide

v20260406

golang-concurrency

Guides Go engineers through concurrency patterns, from goroutine lifecycle ownership and channel best practices to mutex/errgroup usage, leak detection, and structured pipelines so every review or implementation stays leak-free and predictable.

Go Concurrency Channels Context Errgroup SyncPrimitives WorkerPools BestPractices

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Overview

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
Never use time.After in loops — each call creates a timer that lives until it fires, accumulating memory. Use time.NewTimer + Reset
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`	Wait for goroutine completion	`Add` before `go`; Go 1.24+: `wg.Go()` simplifies usage
`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

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-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

References

Info

Category Development

Name golang-concurrency

Version v20260406

Size 15.17KB

Source samber/cc-skills-golang

Updated At 2026-04-08