golang-concurrency

Give every goroutine a clear exit path: pass a context.Context and select on ctx.Done(), or use a done channel, and wait with sync.WaitGroup or errgroup. Detect leaks in tests with go.uber.org/goleak via goleak.VerifyTestMain in TestMain.

Use errgroup when goroutines return errors, need cancellation of siblings on first error, 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. For simple counters and flags prefer typed atomics like atomic.Int64; use sync.Map only for write-once/read-many or disjoint-key workloads.

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 after close. Receivers signal completion through a separate done channel or context cancellation, and the producer selects on that signal alongside its send.

sync.Map is slower for write-heavy workloads with overlapping keys and does not support iteration or length checks well. For frequent writes on shared keys, use a plain map guarded by sync.RWMutex instead; unsynchronized concurrent map access causes a hard crash.