go-concurrency

Give every goroutine three answers before spawning: how it exits, how to stop it, and how to wait for it. Pass a context and select on ctx.Done() in every loop, then verify with goleak.VerifyTestMain in TestMain to catch leaks across tests.

Use channels to pass data between goroutines and coordinate lifecycle, since they communicate ownership transfer. Use sync.Mutex or sync.RWMutex to protect shared struct fields, and sync/atomic for simple counters and flags where lock-free operations suffice.

Use sync.WaitGroup when you only need to wait for goroutines to finish. Use errgroup.Group to collect the first error, errgroup.WithContext to cancel sibling goroutines on failure, and errgroup.SetLimit to bound concurrency instead of hand-rolled worker pools.

time.After creates a new timer on every iteration that cannot be stopped, leaking resources until each timer fires. Reuse a single time.NewTimer with Stop and Reset inside the loop instead.

Only the sender (producer) closes a channel; a receiver closing it can panic if the sender writes afterward. Declare direction in signatures with chan<- and <-chan so the compiler enforces correct usage.

Use sync.Map only for write-once/read-many patterns or disjoint key sets across goroutines. When writes are frequent, keys overlap, or you need iteration and length, a plain map guarded by sync.RWMutex is faster.