What happens inside a system or program when the buffer is completely filled, and how can this lead to a hang?

When the buffer in a Go program is completely filled, further writes to it are blocked until data is read from the buffer. This is because the buffer is limited in size.

If the data producer (writer) continues to try to write to the full buffer, and the consumer (reader) does not read data, then the producer goroutine will be blocked. If the consumer is also waiting for the producer (for example, due to deadlock), a deadlock situation occurs, leading to the program hanging.

Example: a channel with a buffer size of 2, where data is written faster than it is read.