Go Concurrency Pitfalls: Nil Channels, Random Select, and Safe Channel Closing

A software developer shares hard-won lessons from building concurrent programs in Go, focusing on three common pitfalls with goroutines and channels. A nil channel, rather than panicking, blocks forever on sends and receives — a subtle bug that can silently freeze an entire program. Go's select statement picks randomly among simultaneously ready cases, meaning developers cannot assume priority or FIFO ordering without additional logic. Closing a channel must be done exactly once and only by the sender, as sending to a closed channel causes a runtime panic while forgetting to close it leaves receivers hanging indefinitely. The article illustrates these concepts through a practical concurrent URL fetcher that enforces a concurrency limit and shuts down cleanly using buffered channels and sync.WaitGroup.