Go Concurrency

Goroutine Lifetimes

Normative: When you spawn goroutines, make it clear when or whether they

exit.

Goroutines can leak by blocking on channel sends/receives. The GC **will not

terminate** a blocked goroutine even if no other goroutine holds a reference to

the channel. Even non-leaking in-flight goroutines cause panics (send on closed

channel), data races, memory issues, and resource leaks.

Core Rules

• Every goroutine needs a stop mechanism — a predictable end time, a

cancellation signal, or both

• Code must be able to wait for the goroutine to finish

• **No goroutines in init()** — expose lifecycle methods (Close, Stop,

Shutdown) instead

• Keep synchronization scoped — constrain to function scope, factor logic

into synchronous functions

// Good: Clear lifetime with WaitGroup

var wg sync.WaitGroup

for item := range queue {

    wg.Add(1)

    go func() { defer wg.Done(); process(ctx, item) }()

}

wg.Wait()

// Bad: No way to stop or wait

go func() { for { flush(); time.Sleep(delay) } }()

Test for leaks with go.uber.org/goleak.

Principle: Never start a goroutine without knowing how it will stop.

Read references/GOROUTINE-PATTERNS.md when

implementing stop/done channel patterns, goroutine waiting strategies, or

lifecycle-managed workers.

Share by Communicating

"Do not communicate by sharing memory; instead, share memory by communicating."

This is Go's foundational concurrency design principle. Use channels for

ownership transfer and orchestration — when one goroutine produces a value and

another consumes it. Use mutexes when multiple goroutines access shared

state and channels would add unnecessary complexity.

Default to channels. Fall back to sync.Mutex / sync.RWMutex when the

problem is naturally about protecting a shared data structure (e.g., a cache or

counter) rather than passing data between goroutines.

Synchronous Functions

Normative: Prefer synchronous functions over asynchronous ones.

Benefit

Why

Localized goroutines

Lifetimes easier to reason about

Avoids leaks and races

Easier to prevent resource leaks and data races

Easier to test

Check input/output without polling

Caller flexibility

Caller adds concurrency when needed

Advisory: It is quite difficult (sometimes impossible) to remove

unnecessary concurrency at the caller side. Let the caller add concurrency

when needed.

Read references/GOROUTINE-PATTERNS.md when

writing synchronous-first APIs that callers may wrap in goroutines.

Zero-value Mutexes

The zero-value of sync.Mutex and sync.RWMutex is valid — almost never need

a pointer to a mutex.

// Good: Zero-value is valid    // Bad: Unnecessary pointer

var mu sync.Mutex                mu := new(sync.Mutex)

Don't embed mutexes — use a named mu field to keep Lock/Unlock as

implementation details, not exported API.

Read references/SYNC-PRIMITIVES.md when

implementing mutex-protected structs or deciding how to structure mutex fields.

Channel Direction

Normative: Specify channel direction where possible.

Direction prevents errors (compiler catches closing a receive-only channel),

conveys ownership, and is self-documenting.

func produce(out chan<- int) { /* send-only */ }

func consume(in <-chan int)  { /* receive-only */ }

func transform(in <-chan int, out chan<- int) { /* both */ }

Channel Size: One or None

Channels should have size zero (unbuffered) or one. Any other size

requires justification for:

• How the size was determined

• What prevents the channel from filling under load

• What happens when writers block

c := make(chan int)    // unbuffered — Good

c := make(chan int, 1) // size one — Good

c := make(chan int, 64) // arbitrary — needs justification

Read references/SYNC-PRIMITIVES.md when

reviewing detailed channel direction examples with error-prone patterns.

Atomic Operations

Use atomic.Bool, atomic.Int64, etc. (stdlib sync/atomic since Go 1.19, or

go.uber.org/atomic) for type-safe

atomic operations. Raw int32/int64 fields make it easy to forget atomic

access on some code paths.

// Good: Type-safe              // Bad: Easy to forget

var running atomic.Bool          var running int32 // atomic

running.Store(true)              atomic.StoreInt32(&running, 1)

running.Load()                   running == 1 // race!

Read references/SYNC-PRIMITIVES.md when

choosing between sync/atomic and go.uber.org/atomic, or implementing atomic

state flags in structs.

Documenting Concurrency

Advisory: Document thread-safety when it's not obvious from the operation

type.

Go users assume read-only operations are safe for concurrent use, and mutating

operations are not. Document concurrency when:

• Read vs mutating is unclear — e.g., a Lookup that mutates LRU state

• API provides synchronization — e.g., thread-safe clients

• Interface has concurrency requirements — document in type definition

Context Usage

For context.Context guidance (parameter placement, struct storage, custom

types, derivation patterns), see the dedicated

go-context skill.

Buffer Pooling with Channels

Use a buffered channel as a free list to reuse allocated buffers. This "leaky

buffer" pattern uses select with default for non-blocking operations.

Read references/BUFFER-POOLING.md when

implementing a worker pool with reusable buffers or choosing between

channel-based pools and sync.Pool.

Advanced Patterns

Read references/ADVANCED-PATTERNS.md when

implementing request-response multiplexing with channels of channels, or

CPU-bound parallel computation across cores.

Related Skills

• Context propagation: See go-context when passing cancellation, deadlines, or request-scoped values through goroutines

• Error handling: See go-error-handling when propagating errors from goroutines or using errgroup

• Defensive hardening: See go-defensive when protecting shared state at API boundaries or using defer for cleanup

• Interface design: See go-interfaces when choosing receiver types for types with sync primitives

External Resources

• Never start a goroutine without knowing how it will stop

— Dave Cheney

• Rethinking Classical Concurrency Patterns — Bryan Mills

(GopherCon 2018)

• When Go programs end — Go Time podcast

• go.uber.org/goleak — Goroutine leak

detector for testing

• go.uber.org/atomic — Type-safe

atomic operations