What exactly does the selectnbrecv function from Go do?

Question

I'm reverse engineering a Go binary and came across the function selectnbrecv. However, I don't understand the documentation. I'll appreciate it if someone can explain to me the context and operation of the function. Thanks!

Answer 1

It is the Go runtime internal implemetaion for non blocking receive from the channel:
When the channel has any events the selectnbrecv function returns true otherwise returns false (for nil channel returns false): It receives on channel and writes the received data to v (if &v is not nil, in which case received data is ignored.) If no data are available, returns false. Otherwise, if the channel is closed, zeros v and returns true. Otherwise, fills in v with a data and returns true.

// compiler implements
//
//  select {
//  case v = <-c:
//      ... foo
//  default:
//      ... bar
//  }
//
// as
//
//  if selectnbrecv(&v, c) {
//      ... foo
//  } else {
//      ... bar
//  }
//
func selectnbrecv(elem unsafe.Pointer, c *hchan) (selected bool) {
    selected, _ = chanrecv(c, elem, false) // false for non blocking
    return
}