Go developer unpacks channel internals after reading runtime source code

A developer spent a week studying Go 1.26's runtime source files chan.go and select.go to understand how channels work under the hood. Every Go channel is backed by an hchan struct containing a ring buffer, two wait queues for blocked goroutines, and a single runtime mutex that protects all operations. Unbuffered channels carry no buffer at all, requiring sender and receiver to meet simultaneously, with the sender writing a value directly onto the receiver's stack. When a receiver is already waiting, a buffered channel skips the buffer entirely and hands the value over directly, maintaining a strict invariant that data and waiting receivers never coexist. The study also revealed how Go preserves FIFO ordering when a full buffered channel has parked senders, by routing the oldest buffered value to the receiver and placing the sender's value into the freed slot.