golang-concurrency

Give every goroutine a clear exit path: pass a context.Context and include a ctx.Done() case in every select loop, and let callers wait via sync.WaitGroup or errgroup. In tests, use go.uber.org/goleak in TestMain to detect leaked goroutines automatically.

Use errgroup when goroutines return errors, need cancellation of siblings on first failure, or need bounded concurrency via SetLimit. Use sync.WaitGroup only for simple fire-and-wait work with no error propagation; Go 1.25+ offers wg.Go for that case.

Use channels to transfer ownership of data between goroutines, and sync.Mutex or sync.RWMutex to protect shared struct fields with short critical sections. For simple counters and flags, prefer typed atomics like atomic.Int64 and atomic.Bool.

sync.Map fits write-once/read-many caches or disjoint key sets accessed by many goroutines. For write-heavy workloads with overlapping keys, a plain map guarded by sync.RWMutex is faster, and unsynchronized concurrent map access causes a hard crash.

Each time.After call allocates a new timer, causing churn in hot loops. Create one time.NewTimer outside the loop and call Reset after each event; on Go versions before 1.23, drain the channel if Stop reports a pending value.

Only the sender closes a channel; closing from the receiver panics if the sender writes afterward. Receivers signal completion through a separate done channel or context cancellation, and producers select on that signal alongside their sends.